Unfortunately these images are not going to the web, they're going into a software called ARCH which expects JPEGs specifically. And also I've been told that ba

Unfortunately these images are not going to the web, they're going into a software called ARCH which expects JPEGs specifically. And also I've been told that bad things will happen if we give ARCH files bigger than 2 megabytes. The first idea I had was to export multiple versions of the same image at each quality level (0 to 12 in photoshop) and then use the RGB values of each pixel to calculate the RMSE for each one against the JPEG exported with the highest quality settings. This would be assuming that there is an RMSE which roughly corresponds to what my human eyes consider "acceptable amounts of compression artifacts." The images are so big that even though they are being compressed and checked multiple times the computer is still doing the work faster and more thoroughly than I can. And thanks for sharing the link to mozjpeg. It's helping me to understand the differences between different jpeg encoders which is very important.