About optisorl

sorl-thumbnail is a great Django library that takes your stored images and automatically convert them into desired sized thumbnails and store them with nice names in the MEDIA_ROOT. The problem is that the engines that do the resizing often doesn’t do an amazing job of optimizing them. Usually optimizing an image means carefully deleting things the human eye can’t notice anyway. This becomes incredibly relevant when the thumbnail you create is so small in resolution that the user really stands very little chance to notice.

This package, is a pluggable backend to sorl-thumbnail that attempts to do a good job of optimizing the generated thumbnail just right after it has been written to disk.

Installation

First, simply pip install optisorl.

Then add, in your Django settings:

THUMBNAIL_BACKEND = 'optisorl.backend.OptimizingThumbnailBackend'

Then review the sections below about being prepared for PNGs, GIFs and JPEGs.

Optimizing PNGs

optisorl uses a binary called pngquant which is a command line tool that do lossy compression of PNG images and supports alpha transparency. pngquant is BSD licensed. It’s easy to install on most systems. For example brew install pngquant or apt-get install pngquant.

What happens is that when optisorl notices that a thumbnail was created it (and stored in MEDIA_ROOT) it then takes that file and executes pngquant something like this:

pngquant -o /path/file.tmp.png --skip-if-larger -- /path/file.png

Note the --skip-if-larger which means that if the thumbnail is really really small already the resulting optimization might not be any better and it thus omits doing an optimization.

If you want to override the location of the executable pngquant you can set this setting for example:

# in settings.py or equivalent

PNGQUANT_LOCATION = '/opt/special/bin/pngquant2.0'

Optimizing GIFs

optisorl uses gifsicle with level 3 optimization. gifsicle is GPL licensed but use is not restricted by a license. To install it use brew install gifsicle or apt-get install gifsicle.

To override where the gifsicle executable is located you can set in your settings:

# in settings.py or equivalent

GIFSICLE_LOCATION = '/opt/special/bin/gifsicle'

If you want to disable all optimization of GIFs just set GIFSICLE_LOCATION (in your settings.py) to None or False.

Optimizing JPEGs

optisorl uses mozjpeg to optimize JPEGs. It’s a great fit because it almost never reduces the quality such that human eyes can notice it. Especially when the thumbnails are relatively small. The command that we use to execute mozjpeg looks like this:

mozjpeg -outfile DESTINATION -optimise SOURCE

You can override where the executable is by setting:

# in settings.py or equivalent

MOZJPEG_LOCATION = '/my/bin/mozjpeg'

For an example of what kind of results you can get with mozjpeg see this blog post: Examples of mozjpeg savings. Also see blog post mozjpeg installation and sample.

Limitations

Help is most welcome. At the moment…

• Does not support S3 storage

• Unable to NOT optimize images in run-time

• Not possible to override certain pngquant parameters

• Not possible to override certain gifsicle parameters

• Not possible to override certain mozjpeg parameters