MozJPEG - For more efficient JPEG compression

[Beep6581]

Originally reported on Google Code with ID 2639

http://calendar.perfplanet.com/2014/mozjpeg-3-0/
"MozJPEG — is a modernized JPEG encoder that offers better compression while remaining
fully standard-compliant, so it’s compatible with all browsers, operating systems and
native apps"

Reported by entertheyoni on 2015-01-14 12:51:26

[Beep6581]

It would be great.

Reported by vilmantasr on 2015-01-16 10:17:38

[Beep6581]

I've been using mozjpeg for a while on a web site. Works great.

However, one feature when it comes to jpeg optimization is still missing, "psychovisual"
quality optimization, ie auto-choice of compression percent based on image content
and psychovisual analysis. Some images can be compressed at 90 and look as good as
another that requires 97.

To do that I use the additional tool "jpeg-recompress", but it seems like there's some
sort of plan to get that feature natively in mozjpeg.

Reported by torger@ludd.ltu.se on 2015-01-24 10:57:27

[Beep6581]

Note that mozjpeg does not improve image quality, it produces equivalent jpegs but compresses
them better, ie you get somewhat smaller files. To make huge gains in filesize the
largest effect is still to choose a compression level that suits that particular image
though. It's a pain to do manually (trial error) that's why functionality like jpeg-recompress
is so valuable.

Then you don't choose jpeg quality level 0-100, but on a scale according to some psychovisual
measure, and then the tool finds the lowest jpeg quality level that matches that.

Reported by torger@ludd.ltu.se on 2015-01-24 11:03:23

[Kakurady]

I want to add that having smaller files at the same quality, also means the quality can be made greater at the same file size. So saying that mozjpeg improves quality, and that it makes smaller files, can both be correct.

Also mozjpeg uses different quantization tables, so the quality level scale would be different.