Key points before we compare:
- We should compare the images with same dimensions, a larger image always looks better than the smaller one.
- I selected the same images with Zhiye posted before, also added some posters on homescreen randomly.
Actions which can certainly imporve quality:
- Pillow 9.0.0 has better quality(we use 9.0.0 in our demo) with the same params, we are using 7.0.0 on production.
- For jpeg images, make quality = 95 (which is the highest number for common use) can imporve a bit than 75(we are using now) in theory, but it's hard to tell by human eyes. you can check it in compare-jpg.html.
- Still have a color change on webp form, even we save it directly without resize, and make all params highest:
>>> from PIL import Image as PilImage
>>> image = PilImage.open("pillow_images/source_posters/4afd31cc-3d0b-4535-a6ed-26e7a567a73e.jpg")
>>> image.save("pillow_images/source_posters/4afd31cc-3d0b-4535-a6ed-26e7a567a73e.webp", "WEBP", lossless=True, icc_profile=icc_profile, method=6, quality=100)
Xugang used cwebp to do the same thing(jpg->webp with resize) manually, also see the color change, we are still researching it:
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Check canvas jpg with original image in original dimensions: result/compare-canvas.html
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Check canvas jpg with different quality - compare with Mac Preview: result/compare-jpg.html
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Check canvas jpg with webp: result/compare-webp.html
You may need zoom in to see the difference, sometimes you need refresh it on browser if you can not see images. this is not an official test, I can do more test cases or make a full report if necessary.