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Comment by voltagex_ | Hacker News Reader

Simple (UI wise, I'm sure the implementation is tricky), yet very useful.

I wonder if there's a way to represent changes that might not be easily seen - say you ran an image through pngcrush.

"The main purpose of pngcrush is to reduce the size of the PNG IDAT datastream by trying various combinations of compression methods and delta filters." - Wikipedia.

So there will not be any change in the image visually. The 'crushed' image will have the same quality as the source image. So even if you run an image through pngcrush, this new github feature should not find any difference between the original image and the 'cushed' one(I think).

1. This isn't a new feature, its existed for years. 2. Git detects a difference, so github will detect a difference.

That being said, there wouldn't be a visible difference when comparing the two images.

So, what kind of change will the git detect when an image is crushed (when there is no visual difference between original and curshed) ?

As far as git is concerned, the PNG file is just a bag of bits. It will record the changes in the IDAT chunks just as with changes in any other files. The images would appear identical on GitHub because they haven't changed visually.

pngcrush optimizes the file losslessly. Looks the same, smaller file size. Since the file does change, git will see a difference (doesn't care what it looks like). To a user, viewing the diff through this Github feature, it would look like nothing changed between commits.

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