iWaggleVR

Calibrating Hues: How the Sony PlayStation Move knows where it is

If you have played or at least demoed all of the PlayStation Move games currently available (and there are about a dozen of them out there already) you have surely noticed that not even two of them share the exact same start up calibration process – the one that asks you to point the Move somewhere and push a button.

Some of those procedures come with either super simple instructions or super “complex” ones, which means you are often left in doubt as to what the game intends you to do in order to calibrate the device properly. Not only that, some instructions are not very clear either.

Let’s take a look at some examples:

 Tumble

What this screen tells the user is that:

1. He needs to be standing
2. The camera must be located on top of the screen
3. The camera must be tilted at such an angle that the PlayStation Move “line of sight” touches the camera lens perpendicularly.

What the user wonders looking at this screen:
1. Do I really need to be standing to play this game?
2. Does the camera really need to be located on top of the screen despite what Sony’s set-up instructions tell me every time I launch a game?
3. I’m too close for that. Do I need to move back?

 Kung Fu Rider
1st step 

What this screen tells the user is that:
He has to “adjust the PS Eye position and orientation such that the sphere is positioned in the center of the screen”.

What the user wonders looking at this screen:
Is it OK to leave the camera alone and simply relocate myself so that the Move ends up being in the middle of the screen anyway? What if I move back to my original position after that?

2nd step

What this screen tells the user is that:
1. Camera must be level and the Move perpendicular to its lens.
2. He must “take into account the orientation of the motion controller”.

What the user wonders looking at this screen:
1. I have just tilted the camera downwards to comply with what I was instructed to do in the first step. Am I doing it wrong?
2. What does that even mean? I’m already orientating the motion controller towards the camera. Is that a bad thing?

 Flight Control HD

What this screen tells the user is that:

He has to point the Move “at the screen” and press either the Move button or the trigger.

What the user wonders looking at this screen:
Fair enough. It says “at the screen” though. Not at the camera. And it doesn’t specify whether I should point at the center of the screen or at any other point I want. Oh well, let’s see how this goes.

While I’m obviously underestimating the IQ level of the average user here (i.e. of course you have to point at the center of the screen in Flight Control HD), and while it is understandable that different games have different requirements, it’s fair to say that on top of the lack of uniformity in the calibration process among Move compatible games, there is also a general ambiguity in how those procedures are described. Or if not, the exact opposite, with descriptions so detailed they raise more questions than they answer.

As we wait for both the developer community and Sony to come up with better ways to explain to the end user what he is supposed to do in order to calibrate the Move properly, I have put together a possible explanation of what actually happens during the start up calibration process.

Hopefully, a better understanding of the inner workings of the PlayStation Move will help you go through most calibration procedures with more confidence and less doubt.

 Locating the sphere

A lot of stuff happens inside the PS3/Move/PSEye trinity during that single second it takes for the start-up calibration processes to complete. The most important one being locating the PlayStation Move sphere within the camera video feed.

To do so, the PlayStation Eye doesn’t simply look for a glowing sphere. It looks for a blinking one. More specifically, one that lights up with a sequence of red, green and blue colors. Unless you have a light bulb in your room the same size of the PlayStation Move sphere which constantly blinks in RGB, this assures identification of the orb during the image analysis.

Past the sphere identification phase there is a white balancing/brightness tweaking one which has the sphere turn off so that it reverts to its natural white color. By looking at the sphere in this state, the system can understand the lighting of the room the player is located in and do adjustments needed to assure both perfect tracking of the sphere and visibility of the player itself.

By the way, this phase is the reason why you have to keep the Move still during the calibration process. In fact, the system assumes that the unlit sphere is exactly where the RGB blinking occurred a millisecond before, so moving it makes it hard to track. Internal sensors help determine if the controller was moved, and if the system suspects that the controller was moved too much it declares the calibration to have failed.

Interestingly, you might have noticed that despite being asked to hold down the Move button (or the T button, or both) during most games’ calibration procedures, you can actually pass the calibration even by just tapping the button – as long as you keep it still of course. It is my assumption that this is some kind of “mind trick” on Sony’s part as it is more likely for the user to stand still while holding a button instead of quickly tapping it.

Anyway, here is a video of this whole process recorded at normal speed and in slow motion. You can easily see the sphere turning red, then green, then blue and eventually off.


 Coloring the sphere

Once the sphere is “locked” by the camera, the next step is to select which light color should be used for actual in-game tracking.

As you already know, color selection takes into consideration the color scheme of the whole video feed in order to be sure the sphere is lit up with a unique color that highly contrasts with the surrounding environment. While the system has quite a big palette to choose from (16,777,216 colors to be precise), you might have noticed it generally picks magenta tones. I guess this is because color selection goes though some kind of a hierarchy of color options which has the least common ones at the top. Hence the bias towards magenta.

But this is not a mandatory selection system. As games like R.U.S.E., Time Crisis: Razing Storm, MAG and King Fu Rider attest, developers have the option to choose any color they want as long as it doesn’t match one of those composing the video feed image. For this reason, they might even allow the end user to choose one of their liking from a given selection of available colors. 

 Guessing camera tilt

Now this is interesting. During my initial experiments conducted for the purpose of this article, I assumed the calibration process asked the player to point the controller at the screen or the PlayStation Eye in order register the “level” orientation of the Move, the point upon which subsequent calculations about orientation would be performed. To my surprise, I discovered this is not really the case.

Oddly enough, the good old DualShock 3 was an eye opener as it doesn’t rely on any sort of calibration in order to be aware of how it is tilted. I assume this is all due to the accelerometers built into the device, which are of course present in the PlayStation Move as well. They “feel” gravity, which is a force always going in the same direction. Hence the ability of the Move to tell where “down” is, regardless of the calibration. Just like the DualShock 3 could.

So why the need to point the Move towards the screen or the camera then? The most logical conclusion I could come up with is that the Move calibration also does some guessing about where the PlayStation Eye camera is located and how it is tilted relative to the PlayStation Move. After all, how could it properly overlay virtual objects on the device in Augmented Reality applications without knowing from what angle/height the camera is filming the sphere? I might be wrong, but the various experiments conducted on this subject yield results that confirm my assumption. 

 Beyond manual calibration: Auto calibration

This is probably one of the most telling, surprising and fascinating discoveries I made during my attempts at understanding how the PlayStation Move works with regard to the calibration process.

In a nutshell, no matter how badly you calibrate it, the PlayStation Move can fix itself. Or rather, the PS3 fixes it.

Think of the PlayStation Move as a brainless data gatherer and the PlayStation 3 as a brilliant interpreter of that data, constantly crosschecking values for the purpose of assuring everything is working as it should.

What this means is that, even upon failure of the calibration process as intended by the developers, PS3 is fed so much data it can spot contradictions. And resolve them.

Of course I have no idea how the math works under the hood, but the results are pretty clear. As exposed in the video below, you can see how the PS3 automatically corrects idiosyncrasies caused by improper calibration as you simply continue to use the PlayStation Move itself. Sadly, this kind of magic doesn’t apply to every game at this time, which leads me to believe this is something developers have to take account of in their games.

But enough talking. Just look at this montage of Start The Party and EyePet Move Edition experiments to see what this auto-calibration does.

Pretty amazing uh? The more you move the magic wand around, the further the system goes through some sort of auto-calibration process which eventually yields the same results you’d get by properly calibrating it yourself in the first place.

As a consequence of this, it’s fair to say that despite the confusion and uncertainty of the current calibration procedures and instructions, there is no real reason to be overly paranoid about it. Perhaps there is with some games which don’t seem to be able to auto-fix errors, but the necessary tools are definitely there and I’m confident future productions will take advantage of those. It’s still early days after all.

And that is it fellas. Hope you enjoyed the read!

Those of you who didn’t because “tldr”, don’t feel left out. A dedicated iWatch video with a summary of all of the above is currently in the works and will be added to this post very soon.

Here it is :)

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