JPEGs with separate quality settings for luminance and chrominance

[bitsgalore]

From https://jpegclub.org/, section "New cjpeg features":

The -quality option has been extended for support of separate quality settings for luminance and chrominance (or in general, for every provided quantization table slot). This feature is useful for high-quality applications which cannot accept the damage of color data by coarse subsampling settings. You can now easily reduce the color data amount more smoothly with finer control without separate subsampling. The resulting file is fully compliant with standard JPEG decoders.

Could be interesting to create some more test images that use this feature.