Image conversion service

[ferrouswheel]

Implement service to convert from lesser known image types to a set of standard image formats.

We could reimplement image conversion and manipulation in every service, but until it is bundled as part of a library, this will be annoying extra work for service authors.

Thus, an image converter service could be helpful:

• load a wide variety of image formats, including those that are less known outside of
  computer-vision/rendering - e.g. exr.
• load these from different storage systems, S3, ipfs, bytestream, URL
• normalise images
• channel swapping, merging, or dropping