This comparison was done with my complete robust H.261 video coding results and my interim robust H.263 results.
The Bar Graph below shows the image quality (PSNR) and Bits per pixel after being transmitted over an error free channels. The results are shown for both H.261 and H.263 for three types of modulation scheme. The idea is to use the less robust but larger capacity modulation scheme (64-QAM) when the channel is good enough and fall back to more robust schemes as the channel degrades.
The bits per pixel measurement is a measure of image compression and the required channel bitrate required. The sequences were coded at 10 frames per second and the modulation schemes correspond to 15, 30, and 45Kbps for 4, 16, and 64-QAM respectively.
Click on the bar graph below for the full size version.