Lossless compression is generally required in fields such as medical imaging and digital editing, where image quality is of paramount importance.
A simple approach to coding a pair of stereo images together is to jointly encode the corresponding pairs of pixels using an optimal entropy code. This is also equivalent to jointly coding the left image pixel and the difference between the right and left image pixels.
In order be more effective than the best lossless independent image encoding, the bit rate per pixel should be below 4.85. This was not the case; the rate was 6.41 bits per pixel, or 19% compression.