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ImageServer

ImageServer creates resized variants of source images by parsing specially formatted URL requests. The source images can reside on either the same machine as the ImageServer or on a remote machine. The generated image variants are saved as local files on the machine that runs the ImageServer. This makes it convenient to serve static/cached files on subsequent requests, for performance reasons.

Command line scripts can optionally be executed after an image variant has been generated. This is useful for, but not limited to, lossless image optimization. Rate-limiting and logging can be enabled too.

ImageServer is a .NET Standard 2.0 library available as a Nuget package. The ImageServer.Demo project is a simple ASP.NET Core application that demonstrates the intended usage of the ImageServer library. Make sure to set correct paths in appsettings.json before running the demo.

Anatomy of requests

An URL request should be formatted using this pattern:

http://example.com/img/[envelope]-[resizemethod]-[quality|compression]-[postprocessing]/image.jpg

The envelope instruction is mandatory.

  • envelope should be formatted as n1xn2 where n1 is the width and n2 is the height of the envelope. The envelope defines the dimensions of the "box" that the resizemethod operates on.

The resizemethod, quality, compression and postprocessing instructions are optional. If any of these instructions are not provided in the URL request, a default value, or the value specified in the configuration, will be applied.

  • resizemethod can be either of the values contain, cover, scaledown or fill. These values maps directly to the resize methods of the ImageFit library. If this instruction is omitted, the scaledown value is implied.

  • quality applies to JPEG images only, and overrides the default JPEG quality. Valid quality values are in the range 0-100. A value of q75 sets the quality to 75.

  • compression applies to PNG images only, and overrides the default PNG compression level. Valid compression level values are in the range 1-9. A value of c6 sets the compression level to 6.

  • postprocessing instruction accepts the values pp or npp. The value pp enables the post-processing script, if one is configured, regardless of the post-processing script being marked as disabled in the configuration. The value npp skips the post-processing script, if one is configured.

Examples

http://example.com/img/250x250/image.jpg

http://example.com/img/250x250-contain/image.jpg

http://example.com/img/250x250-cover/image.jpg

http://example.com/img/250x250-scaledown/image.jpg

http://example.com/img/250x250-fill/image.jpg

http://example.com/img/250x250-contain-q50/image.jpg

http://example.com/img/250x250-contain-c8/image.png

http://example.com/img/250x250-contain-pp/image.jpg

http://example.com/img/250x250-contain-npp/image.jpg

http://example.com/img/250x250-contain-c8-npp/image.png