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jsummers / bmpsuite

A set of Windows BMP image files, for testing purposes
https://entropymine.com/jason/bmpsuite/
GNU General Public License v3.0
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pal8.bmp and pal8.png differ when opened in MS Paint #14

Closed szali closed 3 years ago

szali commented 4 years ago

When opening the generated g/pal8.bmp and the reference html/pal8.png (both with MS Paint which is quite an authority in BMP), and taking a screenshot of the magnified files to compare pixel values in an editor, some pixels have different green levels (e.g. pixel (7, 63) has green=42 in the png and green=43 in the bmp).

jsummers commented 4 years ago

Acknowledged. It isn't necessarily supposed to be an exact match, but I don't think there's any reason for the numbers to be different in this case.

jsummers commented 3 years ago

The pal8*.png images should be fixed by commit 8e9503e6eea2.

There might still be a few other images with the same type of problem -- I haven't reviewed them all yet.

johnstiles-google commented 8 months ago

Are you still interested in fixing these? rgb16-3103.png and rgb32-7187.png also have low-bit differences compared to my expected output. I'm comparing against Chromium's output, and I will defer to MS Paint if it renders differently. I don't have a Windows machine handy to verify against. (But I suspect they probably agree.)

jsummers commented 8 months ago

I don't know. It'd be nice to review them to see if they're off by more than I'd want, but it's a lot of trouble for something so minor.

For channels that are not exactly 1, 2, 4, or 8 bits, some rounding or dithering is necessary when you convert them to 8 bits. Not everything is going to do that the same way.