These other formats aren't actually generated during upload, but support
for creating them is there.
Also tune the parameters for generating JPEGs:
* Use Q=85 instead of Q=90 because Q=85 enables 4:2:0 chroma
subsampling, while Q=90 doesn't use subsampling. Subsampling reduces
filesize by ~30% in most cases. It does reduce quality for certain
images, particularly for images with lots of bright red, but in most
cases the quality difference isn't noticeable.
* Enable several MozJPEG-specific options, including trellis
quantization and scan optimization. These reduce filesize without
reducing quality, at the cost of slower encoding times.
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