Could you please be so kind as to let me know what compression level you use for prince-jpeg-quality: auto, if you don't mind? Would you say the maximum compression before seeing visible defects would be around 75%? Are you using something similar to the IJG JPEG scale?

Setting a value of "auto" will not perform any recompression, so the JPEG image will be embedded in the PDF exactly as-is. Since we are using jpeglib from IJG, the quality percentage should be based on their metrics.

Thanks Mike. That's great to know since each jpeg lib has their own metrics.