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I was doing a project and ran into this problem: When creating a big ARGB PNG (8192x8192 as an example), sometimes when viewing it in Windows Photo Viewer and other Microsoft programs, the background is shown as BLACK even though I use Color.Transparent or FromARGB(0, 255, 255, 255) or FromARGB(0, 0, 0, 0). After discovering this I created another file with Paint.NET (all transparent, 32bit) just for test And it did the same thing: Sometimes when opened, it indicated transparent, and some times the same file was showing plain black! I also had seen this behavior outputting to TIFF, but at the time I thought it was something I did (not closing a filled polygon or something...)

I also tried with... smaller files, like 1000x1000, and they never had the issue.

I confirmed the behavior at a friends setup (also a Win7, 64bit)... sooo Whats going on? Why cant my Windows 7 PS1 Pro, 64Bit (and most important: the customers setup) not interpret alpha on 'big' files?
TRK3 17-Sep-12 18:18pm    
Assuming the problem only occurs with "Big" files, I'd guess that perhaps the big image is too big to fit into the GPU hardware and so the Microsoft software has to fall back to doing the image processing either in chunks in the GPU or doing it all in the CPU.

Apparently one of those fall-back implementations has a bug in it.

It's certainly not anything we can help you with here, since the bug isn't in your code.

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