pacman ghosts scared

GameInternals aims to spread knowledge of interesting game mechanics beyond the game-specific enthusiast communities. Each post focuses on a specific game mechanic that would normally only be known to high-level players of a particular game, and attempts to explain it in a manner that would be understandable even by readers unfamiliar with that game.

GameInternals articles were researched and written by Chad Birch , a gamer and programmer from Calgary, Alberta, Canada.

Understanding Pac-Man Ghost Behavior

It only seems right for me to begin this blog with the topic that inspired me to start it in the first place. Not too long ago, I came across Jamey Pittman's "Pac-Man Dossier" , which is a ridiculously-detailed explanation of the mechanics of Pac-Man. I found it absolutely fascinating, so this site is my attempt to discover and aggregate similarly-detailed information about other games (albeit in much smaller chunks). However, as a bit of a tribute, I'm going to start with Pac-Man as well, specifically the ghost AI. It's an interesting topic, and hopefully my explanation will be a bit more accessible than Jamey's, due to focusing on only the information relevant to ghost behavior.

About the Game

"All the computer games available at the time were of the violent type - war games and space invader types. There were no games that everyone could enjoy, and especially none for women. I wanted to come up with a "comical" game women could enjoy." - Toru Iwatani, Pac-Man creator

Pac-Man is one of the most iconic video games of all time, and most people (even non-gamers) have at least a passing familiarity with it. The purpose of the game is very simple — the player is placed in a maze filled with food (depicted as pellets or dots) and needs to eat all of it to advance to the next level. This task is made difficult by four ghosts that pursue Pac-Man through the maze. If Pac-Man makes contact with any of the ghosts, the player loses a life and the positions of Pac-Man and the ghosts are reset back to their starting locations, though any dots that were eaten remain so. Other than simply avoiding them, Pac-Man's only defense against the ghosts are the four larger "energizer" pellets located at the corners of the maze. Eating one causes the ghosts to become frightened and retreat for a short time, and in the early levels of the game Pac-Man can even eat the ghosts for bonus points during this period. An eaten ghost is not completely eliminated, but is returned to its starting position before resuming its pursuit. Other than eating dots and ghosts, the only other source of points are the two pieces of fruit which appear during each level near the middle of the maze. The first fruit appears when Pac-Man has eaten 70 of the dots in the maze, and the second when 170 have been eaten.

Every level of Pac-Man uses the same maze layout, containing 240 regular "food" dots and 4 energizers. The tunnels that lead off of the left and right edges of the screen act as shortcuts to the opposite side of the screen, and are usable by both Pac-Man and the ghosts, though the ghosts' speed is greatly reduced while they are in the tunnel. Even though the layout is always the same, the levels become increasingly difficult due to modifications to Pac-Man's speed, as well as changes to both the speed and behavior of the ghosts. After reaching level 21, no further changes to the game's mechanics are made, and every level from 21 onwards is effectively identical.

Common Elements of Ghost Behaviour

"Well, there's not much entertainment in a game of eating, so we decided to create enemies to inject a little excitement and tension. The player had to fight the enemies to get the food. And each of the enemies has its own character. The enemies are four little ghost-shaped monsters, each of them a different colour - blue, yellow, pink and red. I used four different colours mostly to please the women who play - I thought they would like the pretty colours." - Toru Iwatani, Pac-Man creator

Each of the ghosts is programmed with an individual "personality", a different algorithm it uses to determine its method of moving through the maze. Understanding how each ghost behaves is extremely important to be able to effectively avoid them. However, before discussing their individual behaviors, let's first examine the logic that they share.

The Ghost House

When a player begins a game of Pac-Man, they are not immediately attacked by all four of the ghosts. As shown on the diagram of the initial game position, only one ghost begins in the actual maze, while the others are inside a small area in the middle of the maze, often referred to as the "ghost house". Other than at the beginning of a level, the ghosts will only return to this area if they are eaten by an energized Pac-Man, or as a result of their positions being reset when Pac-Man dies. The ghost house is otherwise inaccessible, and is not a valid area for Pac-Man or the ghosts to move into. Ghosts always move to the left as soon as they leave the ghost house, but they may reverse direction almost immediately due to an effect that will be described later.

The conditions that determine when the three ghosts that start inside the ghost house are able to leave it are actually fairly complex. Because of this, I'm going to consider them outside the scope of this article, especially since they become much less relevant after completing the first few levels. If you're interested in reading about these rules (and an interesting exploit of them), the Pac-Man Dossier covers them in-depth (under the "Home Sweet Home" heading) , as always.

Target Tiles

Much of Pac-Man's design and mechanics revolve around the idea of the board being split into tiles. "Tile" in this context refers to an 8 x 8 pixel square on the screen. Pac-Man's screen resolution is 224 x 288, so this gives us a total board size of 28 x 36 tiles, though most of these are not accessible to Pac-Man or the ghosts. As an example of the impact of tiles, a ghost is considered to have caught Pac-Man when it occupies the same tile as him. In addition, every pellet in the maze is in the center of its own tile. It should be noted that since the sprites for Pac-Man and the ghosts are larger than one tile in size, they are never completely contained in a single tile. Due to this, for the game's purposes, the character is considered to occupy whichever tile contains its center point . This is important knowledge when avoiding ghosts, since Pac-Man will only be caught if a ghost manages to move its center point into the same tile as Pac-Man's.

The key to understanding ghost behavior is the concept of a target tile. The large majority of the time, each ghost has a specific tile that it is trying to reach, and its behavior revolves around trying to get to that tile from its current one. All of the ghosts use identical methods to travel towards their targets, but the different ghost personalities come about due to the individual way each ghost has of selecting its target tile. Note that there are no restrictions that a target tile must actually be possible to reach, they can (and often are) located on an inaccessible tile, and many of the common ghost behaviors are a direct result of this possibility. Target tiles will be discussed in more detail in upcoming sections, but for now just keep in mind that the ghosts are almost always motivated by trying to reach a particular tile.

Ghost Movement Modes

The ghosts are always in one of three possible modes: Chase, Scatter, or Frightened. The "normal" mode with the ghosts pursuing Pac-Man is Chase, and this is the one that they spend most of their time in. While in Chase mode, all of the ghosts use Pac-Man's position as a factor in selecting their target tile, though it is more significant to some ghosts than others. In Scatter mode, each ghost has a fixed target tile, each of which is located just outside a different corner of the maze. This causes the four ghosts to disperse to the corners whenever they are in this mode. Frightened mode is unique because the ghosts do not have a specific target tile while in this mode. Instead, they pseudorandomly decide which turns to make at every intersection. A ghost in Frightened mode also turns dark blue, moves much more slowly and can be eaten by Pac-Man. However, the duration of Frightened mode is shortened as the player progresses through the levels, and is completely eliminated from level 19 onwards.

"To give the game some tension, I wanted the monsters to surround Pac Man at some stage of the game. But I felt it would be too stressful for a human being like Pac Man to be continually surrounded and hunted down. So I created the monsters' invasions to come in waves. They'd attack and then they'd retreat. As time went by they would regroup, attack, and disperse again. It seemed more natural than having constant attack." - Toru Iwatani, Pac-Man creator

Changes between Chase and Scatter modes occur on a fixed timer, which causes the "wave" effect described by Iwatani. This timer is reset at the beginning of each level and whenever a life is lost. The timer is also paused while the ghosts are in Frightened mode, which occurs whenever Pac-Man eats an energizer. When Frightened mode ends, the ghosts return to their previous mode, and the timer resumes where it left off. The ghosts start out in Scatter mode, and there are four waves of Scatter/Chase alternation defined, after which the ghosts will remain in Chase mode indefinitely (until the timer is reset). For the first level, the durations of these phases are:

• Scatter for 7 seconds, then Chase for 20 seconds.
• Scatter for 5 seconds, then Chase for 20 seconds.
• Scatter for 5 seconds, then switch to Chase mode permanently.

The durations of these phases are changed somewhat when the player reaches level 2, and once again when they reach level 5. Starting on level 2, the third Chase mode lengthens considerably, to 1033 seconds (17 minutes and 13 seconds), and the following Scatter mode lasts just 1/60 of a second before the ghosts proceed to their permanent Chase mode. The level 5 changes build on top of this, additionally reducing the first two Scatter lengths to 5 seconds, and adding the 4 seconds gained here to the third Chase mode, lengthening it to 1037 seconds (17:17). Regarding the 1/60-of-a-second Scatter mode on every level except the first, even though it may seem that switching modes for such an insignificant amount of time is pointless, there is a reason behind it, which shall be revealed shortly.

Basic Ghost Movement Rules

The next step is understanding exactly how the ghosts attempt to reach their target tiles. The ghosts' AI is very simple and short-sighted, which makes the complex behavior of the ghosts even more impressive. Ghosts only ever plan one step into the future as they move about the maze. Whenever a ghost enters a new tile, it looks ahead to the next tile that it will reach, and makes a decision about which direction it will turn when it gets there. These decisions have one very important restriction, which is that ghosts may never choose to reverse their direction of travel. That is, a ghost cannot enter a tile from the left side and then decide to reverse direction and move back to the left. The implication of this restriction is that whenever a ghost enters a tile with only two exits, it will always continue in the same direction.

However, there is one exception to this rule, which is that whenever ghosts change from Chase or Scatter to any other mode, they are forced to reverse direction as soon as they enter the next tile. This forced instruction will overwrite whatever decision the ghosts had previously made about the direction to move when they reach that tile. This effectively acts as a notifier to the player that the ghosts have changed modes, since it is the only time a ghost can possibly reverse direction. Note that when the ghosts leave Frightened mode they do not change direction, but this particular switch is already obvious due to the ghosts reverting to their regular colors from the dark blue of Frightened. So then, the 1/60-of-a-second Scatter mode on every level after the first will cause all the ghosts to reverse their direction of travel, even though their target effectively remains the same. This forced direction-reversal instruction is also applied to any ghosts still inside the ghost house, so a ghost that hasn't yet entered the maze by the time the first mode switch occurs will exit the ghost house with a "reverse direction as soon as you can" instruction already pending. This causes them to move left as usual for a very short time, but they will almost immediately reverse direction and go to the right instead.

The diagram above shows a simplified representation of the maze layout. Decisions are only necessary at all when approaching "intersection" tiles, which are indicated in green on the diagram.

When a decision about which direction to turn is necessary, the choice is made based on which tile adjoining the intersection will put the ghost nearest to its target tile, measured in a straight line. The distance from every possibility to the target tile is measured, and whichever tile is closest to the target will be selected. In the diagram to the left, the ghost will turn upwards at the intersection. If two or more potential choices are an equal distance from the target, the decision between them is made in the order of up > left > down. A decision to exit right can never be made in a situation where two tiles are equidistant to the target, since any other option has a higher priority.

Since the only consideration is which tile will immediately place the ghost closer to its target, this can result in the ghosts selecting the "wrong" turn when the initial choice places them closer, but the overall path is longer. An example is shown to the right, where straight-line measurement makes exiting left appear to be a better choice. However, this will result in an overall path length of 26 tiles to reach the target, when exiting right would have had a path only 8 tiles long.

One final special case to be aware of are the four intersections that were colored yellow on the simplified maze diagram. These specific intersections have an extra restriction — ghosts can not choose to turn upwards from these tiles. If entering them from the right or left side they will always proceed out the opposite side (excepting a forced direction-reversal). Note that this restriction does not apply to Frightened mode, and Frightened ghosts may turn upwards here if that decision occurs randomly. A ghost entering these tiles from the top can also reverse direction back out the top if a mode switch occurs as they are entering the tile, the restriction is only applied during "regular" decision-making. If Pac-Man is being pursued closely by ghosts, he can gain some ground on them by making an upwards turn in one of these intersections, since they will be forced to take a longer route around.

Individual Ghost Personalities

"This is the heart of the game. I wanted each ghostly enemy to have a specific character and its own particular movements, so they weren't all just chasing after Pac Man in single file, which would have been tiresome and flat." - Toru Iwatani, Pac-Man creator

As has been previously mentioned, the only differences between the ghosts are their methods of selecting target tiles in Chase and Scatter modes. The only official description of each ghost's personality comes from the one-word "character" description shown in the game's attract mode. We'll first take a look at how the ghosts behave in Scatter mode, since it's extremely straightforward, and then look at each ghost's approach to targeting in Chase mode.

Scatter Mode

Each ghost has a pre-defined, fixed target tile while in this mode, located just outside the corners of the maze. When Scatter mode begins, each ghost will head towards their "home" corner using their regular path-finding methods. However, since the actual target tiles are inaccessible and the ghosts cannot stop moving or reverse direction, they are forced to continue past the target, but will turn back towards it as soon as possible. This results in each ghost's path eventually becoming a fixed loop in their corner. If left in Scatter mode, each ghost would remain in its loop indefinitely. In practice, the duration of Scatter mode is always quite short, so the ghosts often do not have time to even reach their corner or complete a circuit of their loop before reverting back to Chase mode. The diagram shows each ghost's target tile and eventual looping path, color-coded to match their own color.

The Red Ghost

The red ghost starts outside of the ghost house, and is usually the first one to be seen as a threat, since he makes a beeline for Pac-Man almost immediately. He is referred to as "Blinky", and the game describes his personality as shadow . In Japanese, his personality is referred to as 追いかけ, oikake , which translates as "pursuer" or "chaser". Both languages' descriptions are accurate, since Blinky's target tile in Chase mode is defined as Pac-Man's current tile. This ensures that Blinky almost always follows directly behind Pac-Man, unless the short-sighted decision-making causes him to take an inefficient path.

Even though Blinky's targeting method is very simple, he does have one idiosyncrasy that the other ghosts do not; at two defined points in each level (based on the number of dots remaining), his speed increases by 5% and his behavior in Scatter mode changes. The timing of the speed change varies based on the level, with the change occurring earlier and earlier as the player progresses. The change to Scatter targeting is perhaps more significant than the speed increases, since it causes Blinky's target tile to remain as Pac-Man's position even while in Scatter mode, instead of his regular fixed tile in the upper-right corner. This effectively keeps Blinky in Chase mode permanently, though he will still be forced to reverse direction as a result of a mode switch. When in this enhanced state, Blinky is generally referred to as "Cruise Elroy", though the origin of this term seems to be unknown. Not even the almighty Pac-Man Dossier has an answer here. If Pac-Man dies while Blinky is in Cruise Elroy mode, he reverts back to normal behavior temporarily, but returns to Elroy mode as soon as all other ghosts have exited the ghost house.

The Pink Ghost

The pink ghost starts inside the ghost house, but always exits immediately, even in the first level. His nickname is "Pinky", and his personality is described as speedy . This is a considerable departure from his Japanese personality description, which is 待ち伏せ, machibuse , which translates as "ambusher". The Japanese version is much more appropriate, since Pinky does not move faster than any of the other ghosts (and slower than Blinky in Cruise Elroy mode), but his targeting scheme attempts to move him to the place where Pac-Man is going, instead of where he currently is. Pinky's target tile in Chase mode is determined by looking at Pac-Man's current position and orientation, and selecting the location four tiles straight ahead of Pac-Man. At least, this was the intention, and it works when Pac-Man is facing to the left, down, or right, but when Pac-Man is facing upwards, an overflow error in the game's code causes Pinky's target tile to actually be set as four tiles ahead of Pac-Man and four tiles to the left of him. I don't want to frighten off non-programmers, but if you're interested in the technical details behind this bug, Don Hodges has written a great explanation , including the actual assembly code for Pinky's targeting, as well as a fixed version.

One important implication of Pinky's targeting method is that Pac-Man can often win a game of "chicken" with him. Since his target tile is set four tiles in front of Pac-Man, if Pac-Man heads directly towards him, Pinky's target tile will actually be behind himself once they are less than four tiles apart. This will cause Pinky to choose to take any available turn-off in order to loop back around to his target. Because of this, it is a common strategy to momentarily "fake" back towards Pinky if he starts following closely. This will often send him off in an entirely different direction.

The Blue Ghost

The blue ghost is nicknamed Inky, and remains inside the ghost house for a short time on the first level, not joining the chase until Pac-Man has managed to consume at least 30 of the dots. His English personality description is bashful , while in Japanese he is referred to as 気紛れ, kimagure , or "whimsical". Inky is difficult to predict, because he is the only one of the ghosts that uses a factor other than Pac-Man's position/orientation when determining his target tile. Inky actually uses both Pac-Man's position/facing as well as Blinky's (the red ghost's) position in his calculation. To locate Inky's target, we first start by selecting the position two tiles in front of Pac-Man in his current direction of travel, similar to Pinky's targeting method. From there, imagine drawing a vector from Blinky's position to this tile, and then doubling the length of the vector. The tile that this new, extended vector ends on will be Inky's actual target.

As a result, Inky's target can vary wildly when Blinky is not near Pac-Man, but if Blinky is in close pursuit, Inky generally will be as well. Note that Inky's "two tiles in front of Pac-Man" calculation suffers from exactly the same overflow error as Pinky's four-tile equivalent, so if Pac-Man is heading upwards, the endpoint of the initial vector from Blinky (before doubling) will actually be two tiles up and two tiles left of Pac-Man.

The Orange Ghost

The orange ghost, "Clyde", is the last to leave the ghost house, and does not exit at all in the first level until over a third of the dots have been eaten. Clyde's English personality description is pokey , whereas the Japanese description is お惚け, otoboke or "feigning ignorance". As is typical, the Japanese version is more accurate, since Clyde's targeting method can give the impression that he is just "doing his own thing", without concerning himself with Pac-Man at all. The unique feature of Clyde's targeting is that it has two separate modes which he constantly switches back and forth between, based on his proximity to Pac-Man. Whenever Clyde needs to determine his target tile, he first calculates his distance from Pac-Man. If he is farther than eight tiles away, his targeting is identical to Blinky's, using Pac-Man's current tile as his target. However, as soon as his distance to Pac-Man becomes less than eight tiles, Clyde's target is set to the same tile as his fixed one in Scatter mode, just outside the bottom-left corner of the maze.

The combination of these two methods has the overall effect of Clyde alternating between coming directly towards Pac-Man, and then changing his mind and heading back to his corner whenever he gets too close. On the diagram above, the X marks on the path represent the points where Clyde's mode switches. If Pac-Man somehow managed to remain stationary in that position, Clyde would indefinitely loop around that T-shaped area. As long as the player is not in the lower-left corner of the maze, Clyde can be avoided completely by simply ensuring that you do not block his "escape route" back to his corner. While Pac-Man is within eight tiles of the lower-left corner, Clyde's path will end up in exactly the same loop as he would eventually maintain in Scatter mode.

Wrapping Up

If you've made it this far, you should now have a fairly complete understanding of the logic behind Pac-Man's ghost movement. Understanding the ghosts' behavior is probably the single most important step towards becoming a skilled Pac-Man player, and even a general idea of where they are likely to move next should greatly improve your abilities. I've never been good at Pac-Man, but while I was researching this article and testing a few things, I found that I was able to avoid the ghosts much more easily than before. Even small things make a huge difference, such as recognizing a switch to Scatter mode and knowing that you have a few seconds where the ghosts won't (deliberately) try to kill you.

Pac-Man is an amazing example of seemingly-complex behavior arising from only a few cleverly-designed rules, with the result being a deep and challenging game that players still strive to master, 30 years after its release.

• The Pac-Man Dossier , Jamey Pittman - practically the only source you need for anything related to Pac-Man. I did some original research to confirm a few statements here and there, but honestly, most of this article is just rearranged and reworded from Jamey's amazing work on the Dossier. Highly recommended reading if you enjoyed this article and would like to learn about the other aspects of the game.
• Pac-Man's Ghost Behaviour Analyzed and Fixed , Don Hodges - explanation of Pinky and Inky's targeting bug and some of the relevant Z80 assembly code.
• All Toru Iwatani quotes come from an interview in Programmers at Work by Susan M. Lammers. The entire interview is available online here .

All Pac-Man Ghost Names and What They Do

• July 5, 2022
• Jason Brown

Who are the ghosts who chase Pac-Man through mazes, across Pac-Land and even over Pac-Man World? Let’s find out as we check all Pac-Man ghost names – and what they do!

Table of Contents

Who are the Pac-Man ghosts?

There are four ghosts in the original Pac-Man (which we rated as top of the best Pac-Man games !): a red ghost, a pink ghost, a cyan ghost and an orange ghost.

Do they all behave differently?

They sure do! Considering Pac-Man was originally released in 1980, it may surprise you to learn that each ghost in Pac-Man has their own behaviour and patterns that they follow, as well as behaviour that they adhere to during what’s known as ‘scatter mode’. All of this are things that you may not even notice during play, but we’re here to shine a light on each ghost and reveal what it is they do!

Who is the red ghost in Pac-Man?

According to one of the attract screens on the English language version of the arcade game, the red ghost is named Shadow – and his nickname is Blinky.

For some reason, it’s the nicknames that stuck with the ghosts, so in general, this one is just known as Blinky. Blinky is perhaps the leader of what’s known as the Ghost Gang; he’s definitely the most deadly ghost – and almost certainly the most likely to catch our little yellow hero. 

What pattern does Blinky follow?

Unlike the others, Blinky speeds up as Pac-Man eats more dots in the maze. With 20 dots remaining in the first maze, Blinky gets faster – but in subsequent mazes, he speeds up even sooner. He’s a very tough enemy to outrun, especially as he follows Pac-Man closely once he’s on his trail – and doesn’t even cease his relentless pursuit during periods when the other ghosts enter scatter mode.

Who is the pink ghost?

Oddly – despite Blinky being the ghost known to speed up – the pink ghost’s ‘real’ name is Speedy. However, she’s more commonly known by her nickname, Pinky. Like the other ghosts, she has her own, very specific patterns of movement.

What pattern does Pinky follow?

Pinky moves around maze walls in an anti-clockwise pattern, but also roughly follows Pac-Man’s movement – targeting four spaces ahead of where the player is headed, which is designed to get out in front of them and cut them off. During scatter mode, Pinky heads for the top left corner and moves in an anti-clockwise, circling motion around the corner walls.

Who is the cyan ghost?

The cyan ghost’s ‘official’, original English-language name was Bashful, but his nickname – and like the others, the name he’s known by now – is Inky. The most unpredictable of the four ghosts, Inky is dangerous because you can’t always know exactly what he’s going to do next!

What pattern does Inky follow?

This is a strange one – though unpredictable, Inky’s behaviour is actually linked to the position of the Ghost Gang’s leader, Blinky. He’ll patrol an area dependent on where Blinky is at any given time – and will become more random the further away from Blinky he is. During scatter mode, Inky will patrol the lower right corner of the maze. You know those moments where you get trapped between two ghosts and can’t get away? That’ll usually be Inky and his random behaviour getting you cornered!

Who is the orange ghost?

Pokey – more commonly known as Clyde – is the one ghost whose name doesn’t rhyme with the others. Poor Clyde – always the outsider! His behaviour reflects this too, cleverly – unlike the others, he just doesn’t seem to have much interest in chasing Pac-Man.

What pattern does Clyde follow?

Though Clyde does chase Pac-Man (in much the same way as Blinky), when he gets within eight spaces of Pac-Man, he starts to retreat into the bottom-left corner of the maze. This is also the area he patrols during scatter mode, making the bottom left Clyde’s Corner!

How do you fight back against the ghosts?

There are four Power Pellets in the maze; when Pac-Man eats one, the ghosts turn temporarily blue – signifying that they can be eaten by the hero! This last for just a short time; the ghosts start flashing between blue and white to demonstrate that they are about to turn back to their normal, dangerous colours – in later levels, the period of time to get your revenge is so brief as to be almost imperceptible. 

How does this affect their movement?

When a Power Pellet is eaten, the ghosts immediately change their movement patterns, regardless of whether they were in their pursuit or scatter modes. They immediately move away from Pac-Man’s position – and at a much slower speed than normal. Other than that initial reversal of chasing Pac-Man, their movement is randomly decided at each intersection they reach. This gives Pac-Man some valuable breathing room to clear dots from the maze – or get his revenge if the ghosts are close enough!

What happens to the ghosts when Pac-Man eats them?

If Pac-Man does eat them, only the ghost’s eyes remain – and they immediately race back to the pen at the centre of the maze, where they regenerate and re-emerge. It’s important to note that they regenerate and return immediately This means that, even if the effects of the Power Pellet are still in play for the other ghosts, it’s possible to have a fully regenerated, non-blue, dangerous ghost (or ghosts) on your tail – as well as having blue ghosts simultaneously running from you!  

Are there other ghosts?

There’s quite a few! Later Pac-Man games introduced new ghosts or simply replaced poor, neglected Clyde. For example, the orange ghost in Ms. Pac-Man is Sue, though her behaviour and appearance are the same as Clyde. To differentiate between them, Sue became purple in later games (and the short-lived, mostly forgotten, animated TV show from 1982). Tim is the name of the orange ghost in Jr. Pac-Man – but again, it’s basically just Clyde with a different name!

Pac-Mania added two new ghosts to Pac-Man’s rogue gallery: Funky and (ahem) Spunky. Funky was a green ghost and Spunky was grey; their only other appearances were in Pac-Man 256 – though they behaved very differently there. Pac-Man 256 also introduced the scary, teleporting Glitchy!

There are many more – especially in Pac-Man and the Ghostly Adventures, which originated as a CGI cartoon. This had a huge cast of individual ghosts with their own characters and very distinct visual characteristics – but the most iconic, famous ghosts remain the four originals from the Ghost Gang: Blinky, Pinky, Inky and Clyde!

This article may contain affiliate links. If you use these links to purchase an item we may earn a commission. Thank you for your support.

Jason – who lives in the UK – has had a lifelong interest in video games, which all started when he discovered Space Invaders in the early 80s. The first game he ever completed was Wonder Boy in Monster Land on the Sega Master System – which remains one of his proudest gaming achievements. Jason is a passionate writer – and has been writing about gaming since the late 90s. He currently runs pop culture blog midlifegamergeek.com, which he updates on a daily basis (and has written more than 700 articles on the blog alone!).

Outside of video games, Jason is a keen tabletop gamer, film buff and comic book fan.

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PBS Explains How Pac-Man's Ghosts Think And Behave

Everyone knows Pac-Man, but not everyone knows that its ghosts possess a little more intelligence than you might think — Game/Show by PBS has all the details.

It's safe to say that pretty much anyone reading this site is familiar with Pac-Man . He's one of the most recognizable characters around, not to mention the immense popularity of his much-ported arcade debut and the fact that his more recent starring roles are still received relatively warmly .

Some parts of the Pac-Man  legend are relatively well-known — for instance, his origins as Puck-Man, a name that was later changed to avoid crude vandalism — but the complexity of the ghosts that are tasked with preventing Pac-Man from successfully eating his fill of pellets and fruit is something that frequently flies under the radar.

Thankfully, this week's edition of PBS Game/Show sees Jamin Warren break down just why the ghosts are so impressive. Each of the four spirits that you're up against has its own individual strategy to take down Pac-Man , and their tactics are perhaps better thought out than you might expect from a game that was released to arcades by Namco some 35 years ago.

For instance, Blinky — known as 'Shadow' in the Japanese version of the game — will head straight for Pac-Man no matter where he is in the maze, following him as closely as his Japanese moniker would suggest. Pinky, on the other hand, is referred to as 'Ambusher' in Japan, and as such will try and predict where the player will go by heading for a position four tiles ahead of Pac-Man .

Inky and Clyde have similarly unique stratagems that Warren analyses in the video, and the whole thing is enough to make you think a little more about what we expect from enemy AI in games. The intelligence of computer-controlled opposition in a game is a difficult thing to judge, as proven by the amount of players who can't tell the ghosts of Pac-Man apart — and that can make it a difficult thing to properly evaluate.

Last year saw The Lord of the Rings: Shadow of Mordor tout its Nemesis system as a potentially game-changing feature , and it wouldn't be too surprising to see more titles try  a similar tactic. As graphical advancements taper off, developers will have to find new was to set themselves apart from the pack, and improved AI could be a prime candidate — and perhaps we have Pac-Man to thank for that.

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Ghosts (Pac-Man)

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The Ghosts are the main antagonists of the Pac-Man franchise.

• 3.1 Wreck-It Ralph
• 3.2.1 Super Smash Bros. for Wii U and 3DS
• 3.2.2 Super Smash Bros. Ultimate
• 3.3 Just Dance
• 3.4 Fortnite
• 3.5 Fall Guys
• 6 Navigation

History [ ]

In the original Pac-Man , the Ghosts chase Pac-Man around a maze to keep him from eating all of the dots. It was the player's objective to avoid the ghosts and collect all of the dots.

Power Pellets are the ghosts' ultimate weakness. When Pac-Man eats one, the ghosts turn blue, and Pac-Man can eat them.

• One Ghost eaten - 200 pts.
• Two Ghosts eaten - 400 pts.
• Three Ghosts eaten - 800 pts.
• Four Ghosts eaten - 1600 pts.

In the original Pac-Man , there were four ghosts (referred to as the Ghost Gang), each member having their own unique personalities:

• Blinky - Red, he is the most aggressive of the ghosts as he chases Pac-Man relentlessly.
• Pinky - Pink, she is deceptive as she strategically ambushes Pac-Man from the front.
• Inky - Cyan, he's friends with Blinky as the two work together to scare Pac-Man into making the wrong move.
• Clyde (Sue in Ms. Pac-Man and Tim in Jr. Pac-Man ) - Orange, he/she's not very smart and flees if Pac-Man get too close.

In the Pac-Man  cartoon series from 1982 to 1984, the Ghost Gang work for Mezmeron and help him try to find the Power Pellet Forest and often call Pac-Man names such as "Pac-Fink".

In the TV series Pac-Man and the Ghostly Adventures , the Ghost Gang work for Lord Betrayus but secretly they help Pac-Man foil Betrayus' plans and hopefully get their bodies back.

Biology [ ]

In the older games and 80's cartoon, the Ghosts were originally portrayed as monsters (some can wield magic) and are considered tangible. However, they had a few ghostly traits such as being able to levitate.

In the Pac-Man and the Ghostly Adventures animated series and games, the Ghosts are portrayed as spectral ectoplasmic entities with the common ghostly traits of being semi-intangible, being able to levitate, and can leave trails of ectoplasm on living beings and the majority of them are former Pac-People.

Other Media [ ]

Wreck-it ralph [ ].

The Ghost Gang appears as supporting characters in Disney's 2012 film Wreck-It-Ralph . While Blinky, Inky, and Pinky can be seen in Game Central Station, Clyde leads the Bad-Anon support group in the Pac-Man game consisting of iconic villains including Dr. Eggman , M. Bison , and Bowser . Clyde is also one of the villains to react when Ralph reveals he does not want to be a bad guy anymore, by turning blue. When Ralph laments how he gets no respect from the others in his game, Clyde suggests that he will just have to accept who he is.

The Ghost Gang makes a cameo in the 2018 sequel Ralph Breaks the Internet .

Super Smash Bros. [ ]

Super smash bros. for wii u and 3ds [ ].

A playable fighter, Pac-Man will summon the ghosts when using a smash attack: Blinky for his side smash, Pinky for his up smash, and Inky and Clyde for his down smash.

The Ghost Gang also appears as an Assist Trophy. When summoned, they wander around the stage as if it was a maze, dealing damage to fighters when collided with. After a few seconds, their movement becomes faster until they wander off. Each Ghost moves similar to the arcade games: Blinky takes the shortest route to reach the enemy, Pinky tries to move in front, Inky moves from behind, and Clyde moves randomly.

In the 3DS version, the Ghosts are hazards for the Pac-Maze stage. They randomly move about the lanes, damaging fighters when contacted. Grabbing a Power Pellet turns the Ghosts blue, and touching them will temporarily bring them out of the battlefield.

Super Smash Bros. Ultimate [ ]

The Ghost Gang returns as an Assist Trophy, reacting just as they did in Super Smash Bros. for Wii U and 3DS . The only difference is that they can be defeated by taking enough hits. They will telegraph their defeat by turning blue before fleeing.

The Ghosts also appear as an advanced primary shield-type spirit. Their spirit battle is against a red Kirby (Blinky), Jigglypuff (Pinky), Squirtle (Inky), and Pac-Man (Clyde) on the Battlefield form of Pac-Land. The Ghost Assist Trophy can also be summoned at random. A blue Ghost named TURN-TO-BLUE also appears as a novice support spirit, which grants the fighter an increase to their speed at the cost of starting the battle at 30% damage. Its spirit battle is a timed battle against four Mr. Game & Watch on the Wrecking Crew stage who tend to avoid conflict.

Just Dance [ ]

Blinky, Pinky, and Inky appear as P2, P3, and P4 in the Just Dance 2019 routine, which shares its name with the series. Pac-Man appears in that routine as P1.

Fortnite [ ]

While not appearing as a skin, the four classic ghosts appear in two crossover cosmetics, in the "PAC-MAN" back bling (appearing as style variations for the default Pac-Man sprite) and cameoing in the "PAC-Brained" emote.

Fall Guys [ ]

In Fall Guys , a costume of a generic ghost (sharing their appearance mostly with Blinky's design in the Pac-World series) was added to the game as part of its fourth free-to-play season, being one of two Pac-Man -themed costumes currently in the game.

Members [ ]

• The Creepies
• Dr. Buttocks
• Kinky Mutation
• Spectral Monsters
• Alien Ghosts
• Aqua Ghosts
• Cyclops Ghosts
• Drill Bit Ghosts
• Fire Ghosts
• Green Ghosts
• Ghost Sharks
• Guardian Ghosts
• Lightning Ghosts
• Tentacle Ghosts
• The Pinky in the Hanna-Barbera cartoon may be a different Pinky, since he and the original (who is a female) are of opposite sexes.
• Despite the modern viewpoint of Pac-Man 's antagonists being spectral beings, this wasn't the original intent of Namco, but rather a result of their appearance making western audiences believe them to be ghosts. In fact, the original Pac-Man only refers to the creatures as generic monsters (with the original Japanese version using the term "Obake", a type of yokai usually equated to goblins), with their cloak-like body merely serving as a sheet covering their true body, being a pink, worm-like being with legs.

Navigation [ ]

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How Do the Ghosts in PAC-MAN Decide Where to Go?

According to Iwatani, all of the ghosts in Pac-Man have their own distinct personality which influences the movements they make. This was a deliberate choice Iwatani made very early on in the game’s development so that, as he said, “they weren’t all just chasing after Pac-Man in single file, which would have been tiresome and flat.”

In fact, only one of the ghosts in Pac-Man actually directly chases the titular hero, Blinky (the red ghost), while the rest have movements that don’t go directly for Pac-Man, but are influenced by Pac-Man’s current position on the screen. You see, the Pac-Man game-board is normally separated into a grid consisting of multiple 8 pixel by 8 pixel squares, known as tiles, with the tile Pac-Man currently resides in generally being the thing used by the ghosts to determine which direction they will go after they transition to a new tile.

In regards to Blinky, along with being the only ghost to actively pursue Pac-Man directly in-game, he’s also the only ghost not  to begin each round inside the small holding pen in the middle of the screen (known by fans as “the ghost house”).

Put simply, Blinky is programmed to target whichever tile Pac-Man currently occupies, giving the illusion that he’s chasing the player. As the game progresses, Blinky’s speed increases to the point that he becomes marginally faster than Pac-Man at which point he becomes what fans refer to as “Cruise Elroy”. The exact number of dots you need to consume for Blinky to become Cruise Elroy depends on which level you’re currently playing, with the overall number dropping the further you get into the game to the point that he will assume Cruise Elroy form when there are still 60 dots left on screen. Blinky will momentarily cease being Cruise Elroy whenever the player loses a life.

As for where the name Cruise Elroy comes from, despite being ingrained as part of Pac-Man lore, nobody seems to know. In the original arcade game, Blinky’s official name is “ Shadow ” alluding to the fact that he is almost always right behind the player. In the Japanese version, his personality is described as “ oikake ” which roughly translates to “ chaser “.

The Pink ghost, known as Pinky, is programmed to try and land on the space 16 pixels (or two tiles in front) of Pac-Man to ambush him. However, due to “overflow error” in the game’s code, if Pac-Man is facing upwards, Pinky will instead attempted to land on the space 4 tiles in front of him and 4 tiles to the left.  Interestingly, because Pinky is programmed to always be ahead of Pac-Man, you can usually make her stop chasing you by heading straight for her.

In the English arcade version of the game, Pinky is known as “Speedy” which many believe is a mistake, since Blinky is the only ghost who can travel faster than the player. However, in the game Super Smash Bros , this apparent misnomer is clarified as follows : “A pink ghost that strategically targets Pac-Man in the Pac-Man series. She’s also known as Speedy, as she can anticipate Pac-Man’s moves and get ahead of him quick enough to ambush him.”

In the Japanese version of the game, Pinky’s personality is described as “ machibuse ” which fittingly translates to “ ambusher “.

The blue ghost, known as Inky, has what has been described as one of the more difficult ghosts to avoid for seasoned players, because his movements appear more erratic than the others. You see, Inky’s movements are determined by both the relative position of Pac-Man and  Blinky.

In a nutshell, Inky will try to move to a tile that is calculated by taking the tile two spaces ahead of Pac-Man and doubling the distance Blinky is away from it. Similar to Pinky, if Pac-Man is facing upwards, this tile will be two tiles ahead of Pac-Man and two tiles to the left. Because of this comparatively complex targeting method, Inky’s movement’s fluctuate a bit, making his English name “ Bashful ” rather appropriate. In the Japanese version, Inky’s personality is described as “ k imagure ” which roughly translates to “ Fickle ” as a nod to his indecisive movements.

As for the final, orange ghost, known as Clyde, his movements are based on how far away he currently is from Pac-Man. Whenever Clyde is more than 8 tiles away from Pac-Man, his movements are identical to that of Blinky’s, in that he will actively attempt to move towards whichever tile Pac-Man is currently occupying.  However,  as soon as Clyde comes within 8 tiles of the circular hero, he will attempt to flee to the bottom left portion of the screen and hide there.

In the English version of the game, Clyde is described as “Pokey”, alluding to his seeming stupidity. In the Japanese version, Clyde comes out a little better, with his personality being listed as “ otoboke ” or “ feigning ignorance “.

Along with this, the ghosts also have three possible modes that they can be in at any one time, Chase Mode, Scatter Mode and Frightened Mode. In chase mode, the ghosts will move exactly as previously described. After a few seconds of gameplay (with the exact amount varying depending on the current level), the ghosts will enter what is known as Scatter Mode, where they will all flee to a different corner of the map, with Blinky heading for the top right, Pinky heading for the top left, Inky heading for the bottom right and Clyde heading for the bottom left.

During Scatter Mode, each ghost’s individual target tile is placed just outside of their respective favourite corner, causing them to endlessly move in circles. The ghosts can only enter Scatter Mode a maximum of 4 times in a given life or level, at which point they’ll enter Chase Mode indefinitely.

As for Frightened Mode, this occurs whenever Pac-Man eats a Power Pellet and is characterised by all of the ghosts turning blue and running away, at which point Pac-Man can eat them. Upon entering Frightened Mode, all of the ghosts will immediately reverse direction and upon reaching a corner, a “psuedo-random number generator” will decide the direction they turn at that point. After Frightened Mode ends, the ghosts will continue with whatever they were doing before. Annoyingly, after moving past level 20, Power Pellets will no longer cause ghosts to become blue.

All of these factors combine to make the four ghosts incredibly difficult to avoid for newer players at higher levels, meaning the game provides a continuous challenge for all but the most skilled aficionados, who can abuse the ghost’s rudimentary AI to move unimpeded around the maps. The master of this sort of thing is Billy L. Mitchell, who is often hailed as the greatest arcade game player of all time- among many other arcade game records being the first to achieve a perfect Pac-Man score of 3,333,360, doing so on July 3, 1999. How does one achieve that score? Simply by managing to eat every dot, bonus, energizer, and ghost on every single level (255 full levels, with a 256th that can’t be completed due to a bug in the game) without ever having Pac-Man die.

If you liked this article, you might also enjoy our new popular podcast, The BrainFood Show ( iTunes , Spotify , Google Play Music , Feed ), as well as:

• The Development of the Video Game “Pong” was a Training Exercise for a New Gaming Developer at Atari and Wasn’t Originally Intended to Be Released
• The Origin of the Legend of Zelda
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• The Surprisingly Long History of Nintendo
• The Rights to Tetris Were Originally Owned by the Soviet Union

Bonus Facts:

• Billy L. Mitchell also was the first known person to achieve more than one million points in Donkey-Kong; the most recent to achieve a score greater than 10 million in Centipede; and for a time held the record for points in Donkey Kong Jr. at 857,300 and then beat that score in 2010, upping it to 1,270,900. On the same weekend in July that year, he also reclaimed the world record in Donkey Kong at 1,062,800. This list goes on and on and on.
• Pac-Man was originally going to be called “Puck-Man” but was changed at the last minute because Western arcade owners were worried people would scratch out part of the P in Puck-Man so that it would say something less than family friendly
• The ghosts in Pac-Man always  leave the ghost house to the left, however, due their programming, they can immediately change direction as soon as leaving depending on where you are.
• In some levels of the game there are “Safe Zones” on the maps where you can hide and, due to the ghost’s programming, will never be caught. Players trying to achieve the maximum score (which takes upwards of three hours of continuous play) often make use of these to rest during marathon sessions.
• Although the ghosts can sometimes move faster than Pac-Man, for example, Blinky when he becomes Cruise Elroy, Pac-Man can always theoretically outrun them because he can turn corners instantly, whereas the ghosts must stop for a brief moment, turn and then continue moving.
• The Pac-Man Dossier
• Understanding Pac-Man Ghost Behavior
• Ghost Psychology
• Blinky, Inky, Pinky, and Clyde: A small onomastic study
• Five things you never knew about Pac-Man
• The Art of Video Games: From Pac-Man to Mass Effect
• Image Source
• Entertainment

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Tonight I found out new words; unimpeded & aficionados. These two words make me want to be an unimpeded aficionade.

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The Pac-Man ghosts have names. Did you know that?

BY SHAWN FARNER

Shawn Farner

PUBLISHED 2 YEARS AGO

If you’re a gamer — and I assume you are — you’ve undoubtedly spent at least some sliver of your life playing Pac-Man. It is a treasured piece of video game history. Remarkably, its core gameplay loop still holds up today. And that loop, of course, is trying to gobble up dots and fruit while avoiding a team of colorful ghosts. But did you know those Pac-Man ghosts aren’t anonymous entities, but instead have actual real names? Is that a thing you knew before this very moment?

They do. And that’s not all.

Yeah, they have freaking names

Pretend you’re you, just out and about, picking up some dots and fruit. There’s a being that wants to stop you from doing so, however. If it touches you, it’ll end your life. How scared would you be if such a being was nameless, orange and have big, round, goofy eyes? Put it on a scale from 1 to 10. Now ask yourself how frightened you’d be if you were being chased by something named Clyde. Instantly adds a couple points, right?

According to this article from ABC , the orange ghost is named Clyde. The red ghost is named Blinky. The pink ghost (quite appropriately) is called Pinky. And the blue/teal ghost is Inky. Every member of this paranormal crew is called something more than “color + ghost.” There are real names happening here.

Two thoughts. First off, it’s not entirely clear why Clyde drew the short straw and didn’t get an “inky” name like everyone else. Second, why go through the trouble of giving them names if they’re all the same? I mean, they do the same thing, right? They don’t have distinct personalities, right? Right?

Yeah, the Pac-Man ghosts have their own personalities, too

In Pac-Man, Clyde, Blinky, Pinky and Inky all behave a bit differently. Knowing that — knowing how each one is prone to act — can actually help you strategize a bit while you’re playing.

To know the personalities of the Pac-Man ghosts, you must know what they were originally called in the Japanese version of the game. Clyde was Stupid, Blinky was Chaser, Pinky was Ambusher and Inky was Fickle. By now you’re probably starting to feel a bit bad for Clyde. He’s not had an easy time in the Pac-Man world.

So what’s it all mean? Clyde is, well… not sharp. He’ll initially seek Pac-Man out, look like he’s on his way, and then veer off to go do his own thing. Blinky, meanwhile, will remain in relentless pursuit of our dot-gobbling lead. No mercy. Pinky is all about the sneak attack and will try to hover around Pac-Man’s general area before moving in to nab a quick kill. Then there’s Inky — a.k.a. Fickle — who can employ just about any strategy in the book at any given time. That’s where the fickle bit comes from.

Now you know more about the Pac-Man ghosts than you ever thought you would

Today you discovered the names of the Pac-Man ghosts — both Western and Japanese. You learned they’re a bit more complex than you imagined, with full-on personalities that play into how they move.

And you learned that someone in game development, way back in 1980, apparently didn’t like another person named Clyde. That is the only explanation for this particular ghost having to endure such disrespect. Or maybe there’s more to the story? Totalisaurus levels of intrigue right here. If someone knows exactly why someone named the “Stupid” ghost Clyde, please let me know.

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Project 4: Ghostbusters

Table of contents, introduction.

• Q1: Exact Inference: Observation
• Q2: Exact Inference: Time Elapse
• Q3: Exact Inference: Full System
• Q4: Approximate Inference: Observation
• Q5: Approximate Inference: Time Elapse
• Q6: Joint Particle Filter: Observation
• Q7: Joint Particle Filter: Time Elapse

I can hear you, ghost. Running won't save you from my Particle filter!

Pacman spends his life running from ghosts, but things were not always so. Legend has it that many years ago, Pacman's great grandfather Grandpac learned to hunt ghosts for sport. However, he was blinded by his power and could only track ghosts by their banging and clanging.

In this project, you will design Pacman agents that use sensors to locate and eat invisible ghosts. You'll advance from locating single, stationary ghosts to hunting packs of multiple moving ghosts with ruthless efficiency.

The code for this project contains the following files, available as a zip archive .

Files to Edit and Submit: You will fill in portions of bustersAgents.py and inference.py during the assignment. You should submit these files with your code and comments. Please do not change the other files in this distribution or submit any of our original files other than these files.

Commenting: There are no particular commenting requirements for this project and comments will not be graded. However, good commenting practice is always recommended.

Evaluation: Your code will be autograded for technical correctness. Please do not change the names of any provided functions or classes within the code, or you will wreak havoc on the autograder. However, the correctness of your implementation -- not the autograder's judgements -- will be the final judge of your score. If necessary, we will review and grade assignments individually to ensure that you receive due credit for your work.

Academic Dishonesty: We will be checking your code against other submissions in the class for logical redundancy. If you copy someone else's code and submit it with minor changes, we will know. These cheat detectors are quite hard to fool, so please don't try. We trust you all to submit your own work only; please don't let us down. If you do, we will pursue the strongest consequences available to us.

Getting Help: You are not alone! If you find yourself stuck on something, contact the course staff for help. Office hours, section, and the discussion forum are there for your support; please use them. If you can't make our office hours, let us know and we will schedule more. We want these projects to be rewarding and instructional, not frustrating and demoralizing. But, we don't know when or how to help unless you ask.

Discussion: Please be careful not to post spoilers.

Ghostbusters and BNs

In this version of Ghostbusters, the goal is to hunt down scared but invisible ghosts. Pacman, ever resourceful, is equipped with sonar (ears) that provides noisy readings of the Manhattan distance to each ghost. The game ends when Pacman has eaten all the ghosts. To start, try playing a game yourself using the keyboard.

The blocks of color indicate where the each ghost could possibly be, given the noisy distance readings provided to Pacman. The noisy distances at the bottom of the display are always non-negative, and always within 7 of the true distance. The probability of a distance reading decreases exponentially with its difference from the true distance.

Your primary task in this project is to implement inference to track the ghosts. For the keyboard based game above, a crude form of inference was implemented for you by default: all squares in which a ghost could possibly be are shaded by the color of the ghost. Naturally, we want a better estimate of the ghost's position. Fortunately, Bayes Nets provide us with powerful tools for making the most of the information we have. Throughout the rest of this project, you will implement algorithms for performing both exact and approximate inference using Bayes Nets. The lab is challenging, so we do encouarge you to start early and seek help when necessary.

While watching and debugging your code with the autograder, it will be helpful to have some understanding of what the autograder is doing. There are 2 types of tests in this project, as differentiated by their *.test files found in the subdirectories of the test_cases folder. For tests of class DoubleInferenceAgentTest , your will see visualizations of the inference distributions generated by your code, but all Pacman actions will be preselected according to the actions of the staff implementation. This is necessary in order to allow comparision of your distributions with the staff's distributions. The second type of test is GameScoreTest , in which your BustersAgent will actually select actions for Pacman and you will watch your Pacman play and win games.

As you implement and debug your code, you may find it useful to run a single test at a time. In order to do this you will need to use the -t flag with the autograder. For example if you only want to run the first test of question 1, use:

In general, all test cases can be found inside test_cases/q*.

Question 1 (3 points): Exact Inference Observation

In this question, you will update the observe method in ExactInference class of inference.py to correctly update the agent's belief distribution over ghost positions given an observation from Pacman's sensors. A correct implementation should also handle one special case: when a ghost is eaten, you should place that ghost in its prison cell, as described in the comments of observe .

To run the autograder for this question and visualize the output:

As you watch the test cases, be sure that you understand how the squares converge to their final coloring. In test cases where is Pacman boxed in (which is to say, he is unable to change his observation point), why does Pacman sometimes have trouble finding the exact location of the ghost?

Note: your busters agents have a separate inference module for each ghost they are tracking. That's why if you print an observation inside the observe function, you'll only see a single number even though there may be multiple ghosts on the board.

• You are implementing the online belief update for observing new evidence. Before any readings, Pacman believes the ghost could be anywhere: a uniform prior (see initializeUniformly ). After receiving a reading, the observe function is called, which must update the belief at every position.
• Before typing any code, write down the equation of the inference problem you are trying to solve.
• Try printing noisyDistance , emissionModel , and PacmanPosition (in the observe function) to get started.
• In the Pacman display, high posterior beliefs are represented by bright colors, while low beliefs are represented by dim colors. You should start with a large cloud of belief that shrinks over time as more evidence accumulates.
• Beliefs are stored as util.Counter objects (like dictionaries) in a field called self.beliefs , which you should update.
• You should not need to store any evidence. The only thing you need to store in ExactInference is self.beliefs .

Question 2 (4 points): Exact Inference with Time Elapse

In the previous question you implemented belief updates for Pacman based on his observations. Fortunately, Pacman's observations are not his only source of knowledge about where a ghost may be. Pacman also has knowledge about the ways that a ghost may move; namely that the ghost can not move through a wall or more than one space in one timestep.

To understand why this is useful to Pacman, consider the following scenario in which there is Pacman and one Ghost. Pacman receives many observations which indicate the ghost is very near, but then one which indicates the ghost is very far. The reading indicating the ghost is very far is likely to be the result of a buggy sensor. Pacman's prior knowledge of how the ghost may move will decrease the impact of this reading since Pacman knows the ghost could not move so far in only one move.

In this question, you will implement the elapseTime method in ExactInference . Your agent has access to the action distribution for any GhostAgent . In order to test your elapseTime implementation separately from your observe implementation in the previous question, this question will not make use of your observe implementation.

Since Pacman is not utilizing any observations about the ghost, this means that Pacman will start with a uniform distribution over all spaces, and then update his beliefs according to how he knows the Ghost is able to move. Since Pacman is not observing the ghost, this means the ghost's actions will not impact Pacman's beliefs. Over time, Pacman's beliefs will come to reflect places on the board where he believes ghosts are most likely to be given the geometry of the board and what Pacman already knows about their valid movements.

For the tests in this question we will sometimes use a ghost with random movements and other times we will use the GoSouthGhost. This ghost tends to move south so over time, and without any observations, Pacman's belief distribution should begin to focus around the bottom of the board. To see which ghost is used for each test case you can look in the .test files.

As an example of the GoSouthGhostAgent, you can run

and observe that the distribution becomes concentrated at the bottom of the board.

As you watch the autograder output, remember that lighter squares indicate that pacman believes a ghost is more likely to occupy that location, and darker squares indicate a ghost is less likely to occupy that location. For which of the test cases do you notice differences emerging in the shading of the squares? Can you explain why some squares get lighter and some squares get darker?

• Instructions for obtaining a distribution over where a ghost will go next, given its current position and the gameState , appears in the comments of ExactInference.elapseTime in inference.py .
• We assume that ghosts still move independently of one another, so while you can develop all of your code for one ghost at a time, adding multiple ghosts should still work correctly.

Question 3 (3 points): Exact Inference Full Test

Now that Pacman knows how to use both his prior knowledge and his observations when figuring out where a ghost is, he is ready to hunt down ghosts on his own. This question will use your observe and elapseTime implementations together, along with a simple greedy hunting strategy which you will implement for this question. In the simple greedy strategy, Pacman assumes that each ghost is in its most likely position according to its beliefs, then moves toward the closest ghost. Up to this point, Pacman has moved by randomly selecting a valid action.

Implement the chooseAction method in GreedyBustersAgent in bustersAgents.py . Your agent should first find the most likely position of each remaining (uncaptured) ghost, then choose an action that minimizes the distance to the closest ghost. If correctly implemented, your agent should win the game in q3/3-gameScoreTest with a score greater than 700 at least 8 out of 10 times. Note: the autograder will also check the correctness of your inference directly, but the outcome of games is a reasonable sanity check.

Note: If you want to run this test (or any of the other tests) without graphics you can add the following flag:

• When correctly implemented, your agent will thrash around a bit in order to capture a ghost.
• The comments of chooseAction provide you with useful method calls for computing maze distance and successor positions.
• Make sure to only consider the living ghosts, as described in the comments.

Question 4 (3 points): Approximate Inference Observation

Approximate inference is very trendy among ghost hunters this season. Next, you will implement a particle filtering algorithm for tracking a single ghost.

Implement the functions initializeUniformly , getBeliefDistribution , and observe for the ParticleFilter class in inference.py . A correct implementation should also handle two special cases. (1) When all your particles receive zero weight based on the evidence, you should resample all particles from the prior to recover. (2) When a ghost is eaten, you should update all particles to place that ghost in its prison cell, as described in the comments of observe . When complete, you should be able to track ghosts nearly as effectively as with exact inference.

• A particle (sample) is a ghost position in this inference problem.
• The belief cloud generated by a particle filter will look noisy compared to the one for exact inference.
• util.sample or util.nSample will help you obtain samples from a distribution. If you use util.sample and your implementation is timing out, try using util.nSample .

Question 5 (4 points): Approximate Inference with Time Elapse

Implement the elapseTime function for the ParticleFilter class in inference.py . When complete, you should be able to track ghosts nearly as effectively as with exact inference.

Note that in this question, we will test both the elapseTime function in isolation, as well as the full implementation of the particle filter combining elapseTime and observe .

For the tests in this question we will sometimes use a ghost with random movements and other times we will use the GoSouthGhost. This ghost tends to move south so over time, and without any observations, Pacman's belief distribution should begin to focus around the bottom of the board. To see which ghost is used for each test case you can look in the .test files. As an example, you can run

Question 6 (4 points): Joint Particle Filter Observation

So far, we have tracked each ghost independently, which works fine for the default RandomGhost or more advanced DirectionalGhost . However, the prized DispersingGhost chooses actions that avoid other ghosts. Since the ghosts' transition models are no longer independent, all ghosts must be tracked jointly in a dynamic Bayes net!

The Bayes net has the following structure, where the hidden variables G represent ghost positions and the emission variables E are the noisy distances to each ghost. This structure can be extended to more ghosts, but only two (a and b) are shown below.

You will now implement a particle filter that tracks multiple ghosts simultaneously. Each particle will represent a tuple of ghost positions that is a sample of where all the ghosts are at the present time. The code is already set up to extract marginal distributions about each ghost from the joint inference algorithm you will create, so that belief clouds about individual ghosts can be displayed.

Complete the initializeParticles , getBeliefDistribution , and observeState method in JointParticleFilter to weight and resample the whole list of particles based on new evidence. As before, a correct implementation should also handle two special cases. (1) When all your particles receive zero weight based on the evidence, you should resample all particles from the prior to recover. (2) When a ghost is eaten, you should update all particles to place that ghost in its prison cell, as described in the comments of observeState .

You should now effectively track dispersing ghosts. To run the autograder for this question and visualize the output:

Question 7 (4 points): Joint Particle Filter with Elapse Time

Complete the elapseTime method in JointParticleFilter in inference.py to resample each particle correctly for the Bayes net. In particular, each ghost should draw a new position conditioned on the positions of all the ghosts at the previous time step. The comments in the method provide instructions for support functions to help with sampling and creating the correct distribution.

Note that completing this question involves removing the call to util.raiseNotDefined(). This means that the autograder will now grade both question 6 and question 7. Since these questions involve joint distributions, they require more computational power (and time) to grade, so please be patient!

As you run the autograder note that q7/1-JointParticleElapse and q7/2-JointParticleElapse test your elapseTime implementations only, and q7/3-JointParticleElapse tests both your elapseTime and observe implementations. Notice the difference between test 1 and test 3. In both tests, pacman knows that the ghosts will move to the sides of the gameboard. What is different between the tests, and why?

To run the autograder for this question use:

Congratulations! You are now a ghostbuster!

Submit your zip to the Homework 5 dropbox on Carmen .

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A list of all ghosts from the series. They were once Pac-Worlders who attacked the globe until they were defeated, had their corporeal bodies sealed in the repository and banished to the netherworld, until Pac-Man accidentally released them.

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• Ghost Family
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Creepy is a ghost that appeared exclusively in Minecraft x Pac-Man . As his name would suggest, he's basically a ghost with the powers of a Creeper.

Appearance [ ]

Creepy is a green ghost with eyes that have black sclera and white pupils, along with the signature mouth of a Creeper.

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Pac-Man Ghost Scared 2

Pac-Man Ghost Scared 2 - Sound Clip

Pac-Man Ghost Scared 2 - Sound clip The 'Pac-Man Ghost Scared 2' sound clip is made by ZozV. This sound clip contains tags: ' pac man ', ' ghost ', ' scared ', ' 2 ', ' lol ', ' meme ', ' funny ', ' original ', ' mp3 ', ' download ', ' soundboards ', ' video games ', ' arcade retro ', . . This audio clip has been played 1429 times and has been liked 3 times. The Pac-Man Ghost Scared 2 sound clip has been created on Jul 30, 2020 Clips Cannot find your favourite sound clip or soundboard? You can always create your own meme sound effects and build your own meme soundboard. With our social media integrations, it is also possible to easily share all sound clips.

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