>>755511PNG standard includes post-decode gamma correction using a custom gamma curve because PNG standard is insane.
Image 1 is in standard brightness range and image 2 is crushed into the top sixteenth of brightness range.
4chan's thumbnailer (and iOS and OSX) ignores this, so thumbnail contains a dither of non-gamma-corrected pixels of image 2 (which look almost solid white) and non-gamma-corrected pixels of image 1 (which looks like image 1).
Browser does support gamma correction curve, so full image looks like a dither of gamma-corrected image 1 (which looks solid black) and gamma-corrected image 2 (which looks like image 2).
