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Update notes for 2023-03-28

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Alan Orth
2023-03-28 23:38:38 +03:00
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content/posts/2023-03.md
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@ -547,5 +547,39 @@ $ magick convert reference.jpg -quality 85 jpg:- | convert - distorted-lossless.
- In an attempt to quantify the generation loss from DSpace's "JPG JPG" method of creating thumbnails I wrote a script called `generation-loss.sh` to test against a new "PNG JPG" method
- With my sample set of seventeen PDFs from CGSpace I found that _the "JPG JPG" method of thumbnailing results in scores an average of 1.6% lower than with the "PNG JPG" method_.
- The average file size with _the "PNG JPG" method was only 200 bytes larger_.
- In my brief testing, the relationship between ImageMagick's `-quality` setting and WebP's `-define webp:lossless=true` setting are completely unpredictable:
```console
$ magick convert img/10568-103447.pdf.png /tmp/10568-103447.webp
$ magick convert img/10568-103447.pdf.png -define webp:lossless=true /tmp/10568-103447-lossless.webp
$ magick convert img/10568-103447.pdf.png -define webp:lossless=true -quality 50 /tmp/10568-103447-lossless-q50.webp
$ magick convert img/10568-103447.pdf.png -quality 10 -define webp:lossless=true /tmp/10568-103447-lossless-q10.webp
$ magick convert img/10568-103447.pdf.png -quality 90 -define webp:lossless=true /tmp/10568-103447-lossless-q90.webp
$ ls -l /tmp/10568-103447*
-rw-r--r-- 1 aorth aorth 359258 Mar 28 21:16 /tmp/10568-103447-lossless-q10.webp
-rw-r--r-- 1 aorth aorth 303850 Mar 28 21:15 /tmp/10568-103447-lossless-q50.webp
-rw-r--r-- 1 aorth aorth 296832 Mar 28 21:16 /tmp/10568-103447-lossless-q90.webp
-rw-r--r-- 1 aorth aorth 299566 Mar 28 21:13 /tmp/10568-103447-lossless.webp
-rw-r--r-- 1 aorth aorth 190718 Mar 28 21:13 /tmp/10568-103447.webp
```
- I'm curious to see a comparison between the ImageMagick `-define webp:emulate-jpeg-size=true` (aka `-jpeg_like` in cwebp) option compared to normal lossy WebP quality:
```console
$ for q in 70 80 90; do magick convert img/10568-103447.pdf.png -quality $q -define webp:emulate-jpeg-size=true /tmp/10568-103447-lossy-emulate-jpeg-q${q}.webp; done
$ for q in 70 80 90; do magick convert /tmp/10568-103447-lossy-emulate-jpeg-q${q}.webp /tmp/10568-103447-lossy-emulate-jpeg-q${q}.webp.png; done
$ for q in 70 80 90; do ssimulacra2 img/10568-103447.pdf.png /tmp/10568-103447-lossy-emulate-jpeg-q${q}.webp.png 2>/dev/null; done
81.29082887
84.42134524
85.84458964
$ for q in 70 80 90; do magick convert img/10568-103447.pdf.png -quality $q /tmp/10568-103447-lossy-q${q}.webp; done
$ for q in 70 80 90; do magick convert /tmp/10568-103447-lossy-q${q}.webp /tmp/10568-103447-lossy-q${q}.webp.png; done
$ for q in 70 80 90; do ssimulacra2 img/10568-103447.pdf.png /tmp/10568-103447-lossy-q${q}.webp.png 2>/dev/null; done
77.25789006
80.79140936
84.79108246
```
- Using `-define webp:method=6` (versus default 4) gets a ~0.5% increase on ssimulacra2 score
<!-- vim: set sw=2 ts=2: -->