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Due to the CLA thing this PR will need to be merged by a repo admin, as we've done on the PEPs repo (explanatory comment).

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What's needed is for the CLA bot to work. I ran into this on another issue a few weeks ago.

@terryjreedy Fixing geldata/cla-bot#50 , at least for the specific issue @AA-Turner is running in to...

(Oops, somehow the comment didn't get submitted with the review)

EDIT: Since I can't dismiss/re-request the approving review or add a request-changes review mark as draft (though the approach I suggest in python/core-workflow#460 could enable that, if we want it), I've added the do-not-merge tag as an additional reminder against merging until the issue above is fixed.

Due to inefficient downsampling and compression, the 128 x 128 version in the PR was barely any smaller than the original (7.8 KB vs 9.7 KB) despite having 16 times fewer pixels. With a more efficient downsampling strategy (nearest neighbor), using a 8-bit palette (like the original) and running optipng with optimal settings, this by be reduced by a further 3x to only 2.6 KB with no loss of perceptible quality; see attached.

python-logo-128x128_2.zip

Also, nitpick but just curious—is there a reason the CSS filename uses underscores, while everything else uses hyphens?

Due to inefficient downsampling and compression, the 128 x 128 version in the PR was barely any smaller than the original (7.8 KB vs 9.7 KB) despite having 16 times fewer pixels. With a more efficient downsampling strategy (nearest neighbor), using a 8-bit palette (like the original) and running optipng with optimal settings, this by be reduced by a further 3x to only 2.6 KB with no loss of perceptible quality; see attached.

python-logo-128x128_2.zip

What settings did you use?

I can perceive a loss of quality (on a Retina screen), this one has more jagged edges:

Original	This one

Screenshot:

Original:

This one:

Actually, let's use an SVG instead. The resized one has a bit fuzzy edges. The SVG has much cleaner lines, like the unresized PNG currently at https://devguide.python.org/

https://commons.wikimedia.org/wiki/File:Python-logo-notext.svg is 5.37 KB, and squashes down 40.83% to 2.19k with https://jakearchibald.github.io/svgomg/

I just used ImageMagick's 'mogrify' command with '-antialias', I didn't realise we were optimising for filesize!

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What settings did you use?

I can perceive a loss of quality (on a Retina screen), this one has more jagged edges:

That's because of the nearest neighbor resampling strategy, which does result in some loss of quality along edges (which wasn't too perceptible on my non-hiDPI 1200p monitor unless I was looking carefully for it) and can cause more serious issues in areas of dense, high-contrast detail (particularly small text, such as in a screenshot), but can dramatically reduce file size by reducing color consistency and ballooning the total number of colors in the palette caused by interpolation-based strategies like bicubic and Lanczos, which appeared to be the main culprit behind the file size barely decreasing when downscaled by 16x here.

However, it's typically better to downscale from the original PNG/SVG, or just use the optimized SVG directly, as it results in no loss of quality (if not higher quality on HiDPI displays) with a similar or smaller filesize to the PNG -> PNG downscale using the aggressive nearest-neighbor strategy, I wasn't able to find a SVG of just the Python logo on the official Python logo page, and was too lazy didn't want to crop it manually and not have it come out the same, so I didn't go ahead with that. But seeing as there is one, and it actually optimizes smaller than even the most aggressive PNG while displaying better, using the optimized SVG as you suggest seems to be a no-brainer.

Additionally, I note that the nominal size of that SVG is 110px x 109px, which it should default to (unless the original theme stylesheet is using width: 100% instead of max-wdith: 100%), which is actually closer to the size that we originally wanted. Therefore, we might not actually need the stylesheet, though as @hugovk mentions it may improve rendering performance and avoid relayouts when rendering since it gives the browser the exact image size before downloading it.

I didn't realise we were optimising for filesize!

Oh, well that was @ezio-melotti 's stated reason for requesting this change,

By resizing it, the page will load faster because it will have to download a smaller image

so I figured if we were doing it, we may as well get the benefit of it.

AFAIK, per our discussion it should just include the optimized SVG, which will work lossleslly for all sizes.

Switched to vector logo, I don't think there are any more outstanding points?

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