> Why do you think it wouldn't work for a JPEG? I just made one like that, and it worked just fine.

JPGs are lossy encodings; my use-case would definitely not work with JPGs, not matter how high you put the quality.

For testing a display (like displaymate does) you literally want to light up specific pixels with specific colors. You can't do that with JPGs.

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derefr a day ago | parent [-]

You can do that with JPEGs, just not the obvious way (i.e. by exporting the JPEG at the target resolution.)

Instead, you need to export the JPEG at a resampled resolution that's a multiple of your target resolution, such that each pre-transform source-image pixel gets mapped to its own entirely-independent JPEG color block.

Most obvious (though perhaps not optimal?) approach: nearest-neighbour upscale your image by 8x, and then save as JPEG with 100% quality (which will create 8x8 blocks with 4:4:4 subsampling.)

	▲	lelanthran 9 hours ago \| parent [-]
		> You can do that with JPEGs, just not the obvious way (i.e. by exporting the JPEG at the target resolution.) Yeah, I don't think GP did it that way.