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I'm confused by the choice of image format. Why use dithered grayscale PNGs for these photos when a full color JPEG at the same bit rate looks a hundred times better. Are they just sacrificing quality for the sake of a low tech aesthetic, without regard for actual efficiency?

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It seems to be purely about aesthetics and ridicules other things said on the page. JPEG would not only be quicker to decompress but could also be much smaller for a similar "geeky" look.

The image aesthetic is emulating the appearance of a dot-matrix printer. It's just a low-tech motif to go with the publication.

That would be all well and good, but the page specifically claims that using dithered images lowers energy use.

They may have ran metrics on decoding processing time neé energy usage

I doubt it. The only study I could find on energy usage in image decoding was this

https://ieeexplore.ieee.org/document/7168333

which found JPEG decoding to be much less energy intensive than PNG decoding, mostly because it's faster. Note that that's not just a function of file size, as lower quality JPEGs actually took more energy to decode.

Which all makes a lot of sense when you consider how much work has gone into optimizing frequency domain based compression and decompression.

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