Running my PC on Win7x64 and serving Subsonic 5.2.1 (build 4427) on an Asustor AS-602T
For cover-art I use different sizes for cover.jpg and resize to 300x300px for folder.jpg.
I had issues with pictures displayed black and white as
Teal and
Coral.
When playing around with batch-scripts to replace all embedded images with the 300x300 folder.jpg I noticed the color-bug remained on individual albums. Then I noticed they all had a resolution of either 72dpi or 96dpi, and resampling it to 300px solved the issue.
Extracted JPGs from MP3s using Metamp3 v0.91, and resized images and changed resolution using mogrify.exe from ImageMagick 7.0.0-0 Q16.