I am trying to optimize a set of JPEGs photos (5120 x 2880 px) that will be used on the web for retina screens.
The objective is to reduce file size as much as possible while keeping image quality high (no really bad compression artifacts). The challenge is that I don't own a retina display myself and I am unsure about the best tools (online vs software) to perform compression.
As I am running on Linux, I tried Gimp with the following settings (50% quality compression, 4:2:0 (chroma quartered)), but I am having a hard time to figure out when the image quality turns bad:
Are there any objective criteria or automated processes to find optimal values for smallest possible sizes?