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JNewt
Joined: 05 Jun 2008
Posts: 69
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 Posted: Wed Oct 22, 2008 9:45 am Post subject: LodePNG bug + fix |
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The Problem: The lodepng decode function was loading greyscale images fine for me, but only returning about a quarter of RGBA images. I've traced the issue back to this line in Common.d:
| Code: | 312 uint bytesPerPixel(ref PngImage image)
313 {
314 return image.bitDepth / 8;
315 } |
I believe it should read like this:
| Code: | uint bytesPerPixel(ref PngImage image)
{
return image.bpp / image.bitDepth;
} |
Fixing this on my local copy and building/installing resolved all my image loading problems, and I thought that it should be reported and fixed. |
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Kosmonaut
Joined: 22 Jun 2008
Posts: 10
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| Posted: Thu Oct 23, 2008 6:28 pm Post subject: |
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This doesn't work for all the images. Remember that
It was just lucky that it worked. Anyways there's something not working with LodePng, I doesn't work anymore for me either. |
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Kosmonaut
Joined: 22 Jun 2008
Posts: 10
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| Posted: Fri Oct 24, 2008 12:51 am Post subject: |
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DISREGARD THAT... I SUCK... at graphics programming. 
The bytesPerPixel method is called when the image is reconstruted, specifically:
| Code: |
// lodepng.Decode.d : 150
...
return decompressor.reconstructImage()[0..info.image.width * bytesPerPixel(info.image) * info.image.height];
...
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The problem is that the bytesPerPixel method returns the bytes per channel (bitDepth = bits per channel), not the bytes per pixel. I think the solution could be:
| Code: |
uint bytesPerPixel(ref PngImage image)
{
return image.bpp / 8;
}
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And now you have the bytes per pixel  |
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JNewt
Joined: 05 Jun 2008
Posts: 69
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| Posted: Tue Oct 28, 2008 4:56 pm Post subject: |
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| As it is possible (albeit unusual) for images to have 16 bit color channels (2 ubytes/channel), I believe my proposed revision is the proper one. The one you've proposed will only work with images with 1 ubyte per channel. |
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Lutger
Joined: 25 May 2006
Posts: 91
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| Posted: Sun Nov 02, 2008 6:53 am Post subject: |
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My apology for this bug, I have updated lodepng with a fix. Thanks for bringing it up, nice to know people are actually using it 
Kosmonaut had the proper fix, quite the mistake I made.
It also works for 16 bit images, see Decode line 212:
bpp = numChannels(colorType) * bitDepth
thus with 16 bit RGBA bpp will be 4 * 16 == 64 bits and bytesPerPixel will return 64 / 8 == 8 bytes.
I hope to have a bit more time soon to work a bit on lodepng. Please do post here or email me if you find any more problems. |
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