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I downloaded an app from Cydia called "Conway's Game of Life" to both my iPhone and my computer. On the iPhone it renders correctly, but on the computer some of the PNG files of the Cydia .deb archive are corrupt. Their thumbnails are totally black and when opened with a simple program like Windows Photo Viewer they appear blank, but in the correct height and width measures. I looked into that and these signs indicate that they are corrupted (also GIMP couldn't open it saying it's corrupted). The same thing happened when I tried downloading different apps.

I don't actually run the .deb files on my computer, but I unzip them and check their contents (I tried with two programs, 7-Zip and AnytoISO, and they both produced the same corruption results, so problem doesn't lie in the unzipping programs).

Any ideas why and how I can solve this? I need them to display correctly on the computer.

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Which computer operating system are you running? Please define "corrupt". You can't post an image yet, but can you post a link to a screenshot showing the corruption. – ChrisF Oct 3 '12 at 10:59
I'm running windows 7. Corrupt = the image is all black, and when opened it's just blank, but still maintains the original height and width. – Dimen Shaw Oct 3 '12 at 11:09
Edit this information into your question – ChrisF Oct 3 '12 at 11:09
How do you have an IOS app running on a computer? – Journeyman Geek Oct 3 '12 at 11:24
Though now I re-read your comment I'm also wondering how you have an iOS/OSX application running on Windows. – ChrisF Oct 3 '12 at 11:29
up vote 2 down vote accepted

I think I know what the problem is. Both in OS X and iOS, apple does something to png files. Apple optimizes a lot of their files so that the perform better inside of apps. However, according to Cydia and Pod2G, optimized pngs will NOT open correctly on a computer. This is similar to how you can't edit themes if you have optimized them in advanced settings. There is no way to view them correctly.

You can try this though. If you know the location from where you got the app, you can use wget to download the file directly to your computer. You may be able to open it there. However you will need a program such a Cygwin to use the command on Windows. Great program actually.

share|improve this answer
So Apple creates non-standard proprietary PNGs? Does anyone know the encoding details? Shouldn't be difficult to develop a PC-based viewer if the format details are known. – Karan Oct 3 '12 at 16:54
Most people probably don't know. First of all, only jailbreak users are going to be aware of such a feature and how many of them tried to figure out how Apple's optimization works. If anyone does know, that would be very helpful. – Josiah Oct 3 '12 at 17:14
Everybody who's looking for information about Apple's png standard: The optimization is specific for iPhone's apps. – Dimen Shaw Oct 4 '12 at 9:28
Thanks. I really appreciate it. – Josiah Oct 4 '12 at 14:45

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