Monday, 14 December 2009

New Versions and Fixing Glitches.

Many users have pointed out to us glitches in their Piku-Piku. I hope that it doesn't upset anyone to see their pictures deform in unnatural ways! But, I thought you might want to know what causes the glitch.

In order to make a Piku-Piku, we need to do some kind of image processing on your image pair. We say that two pixels (one from each image) match if those pixels are the image of the same point in the world. So, for each pixel in one of your images, we need to find the matching pixel in the other image. If we can do that accurately, we can infer how much parallax the point should have (closer points should move more than distant points). And if we get that right, for every pixel, the little animation will look great.

Sounds easy? It isn't. There are three big problems. The first one is the wallpaper effect. But some of you know it as the striped scarf effect, and others as the wonky railings effect; still others as the magic sliding floor. Some bits of your image just look too much like other bits of your image, and, as a result, the matcher can erroneously put a whole region at the wrong depth.

The second problem is that it's just not a well-posed question. Some pixels don't have exactly one match! Something in the background might be hidden (occluded) in one view but visible in the other. Pixels near the edge are often cropped out in the other view. Or a pixel could be on a transparent reflective surface like a window, and match two different pixels. These pixels have to be filled in with some pragmatic and approximate techniques. Yes, I do mean that it's a total hack job.

And the third problem is thin structures. They so easily get attached to the thing behind them and move as if they were a line painted on the background. Yuck!

I realise that by now you're thinking that I've covered pretty much every pixel in your image. It's not easy to plan to avoid these issues, and I wouldn't want you to. Rather, when you see a glitch, instead of thinking it doesn't work, we'd like you to think that it doesn't work yet. To encourage you to think this way, we've released a new version of the image processing software! If you have glitches on your pictures then we invite you to switch to version 2. You can do that by viewing your album or photo and clicking on the '2' at the bottom next to the word 'Version'. In the album view, your images will be back to 'processing...' and then they'll appear. There are plenty more 'new versions' to come ... and not all of them are just about fixing glitches.

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