An imgproxy preset is a named set of processing options. Presets can be used in URLs to make shorter and more human-readable.
A preset definition looks like this:
%preset_name=%processing_options
Processing options should be defined in the same way they are defined in URLs. For example, here's a preset named awesome that sets the resizing type to fill and the resulting format to jpg:
awesome=resizing_type:fill/format:jpg
Read how to specify your presets with imgproxy in the Configuration guide.
A preset named default will be applied to each image. This is useful when you want your default processing options to be different from the default imgproxy options.
Setting IMGPROXY_ONLY_PRESETS to true switches imgproxy into "presets-only mode". In this mode, imgproxy accepts a presets list as processing options just like you'd specify them for the preset option:
http://imgproxy.example.com/unsafe/thumbnail:blurry:watermarked/plain/http://example.com/images/curiosity.jpg@png
All othe URL formats are disabled in this mode.