mozjpeg does Trellis quantization, there is no detailed explanation about jpegmini, a guess is it optimizes the DCT similarly to how it is described in this paper:
http://vision.arc.nasa.gov/publications/sid93/sid93.pdf
http://spie.org/Publications/Proceedings/Paper/10.1117/12.87... http://spie.org/Publications/Proceedings/Paper/10.1117/12.87...
mozjpeg does Trellis quantization, there is no detailed explanation about jpegmini, a guess is it optimizes the DCT similarly to how it is described in this paper:
http://vision.arc.nasa.gov/publications/sid93/sid93.pdf