Allow to do a lossless jpeg to jpeg optimization using mozjpeg only

[flozz]

Add choices for JPEG optimization:

• Guetzli + MozJPEG

  • Always reencode JPEGs using Guetzli and then use additional MozJPEG (lossless) optimization

• MozJPEG

  • Always reencode JPEGs using libjpeg and then optimize losslessly with MozJPEG

• MozJPEG lossless

  • If the input image is already a JPEG: only perform a lossless optimization using MozJPEG (ignore the quality parameter)
  • If the input image is not a JPEG: encode the image using libjpeg (Pillow) and then optimize it with MozJPEG (lossless)

Related issue: flozz/yoga-image-optimizer#15

[nekohayo]

Reiterating my +1000 enthusiasm for this: "perfect encoding" sounds like a very different usecase from "good-enough, but fast" encoding (i.e. "I have hundreds of images to encode, I don't have all day, I need them uploaded to the web or attached to my email ASAP"), so there really ought to be an encoder choice to be able to say "MozJPEG only" in some way.

To put things in perspective, today I tried encoding 4 simple photos, whose original resolution were 3840x2160, and asked Yoga to encode them as 1920x1080 JPEGs... and it took a solid 10-15 minutes to do so. There was a 4 minutes time difference between the 1st image being transcoded and the 4th image being transcoded. In comparison, the same process with pure MozJPEG would have taken a grand total of about 10 seconds or less, but the visual difference would be imperceptible to 99% of humans.

[flozz]

Hello,

Sadly I don't have time to work on this right now... But it is the next feature on my TODO list for YOGA :)