Reposted from the VMware Vroom! blog. By Lawrence Spracklen, VMware
We have talked in previous posts about the ability in View 5 to disable build to lossless (BTL). When BTL is disabled, PCoIP rapidly builds the client image to a high quality, but lossy image — by default, if the image remains constant, PCoIP would continue to refine the image in the background until it reaches a fully lossless state. Stopping the build process when the image reaches the "perceptually lossless" stage can deliver significant bandwidth savings — for typical office workflows, we are seeing around a 30% bandwidth reduction.
Furthermore, in many situations, the difference between fully lossless and perceptually lossless images can be virtually impossible to discern. During our VMworld presentation, we used the following image to emphasize the quality of perceptually lossless:
In this qualitative comparison, we present a zoom-in of two small images. For both images, View fully lossless and View perceptually lossless (no BTL) images are shown side-by-side for comparison — hopefully conveying how difficult it is, even when zoomed, to find differences.
To further emphasize the perceptually lossless quality, it’s also interesting to examine quantitative data — for example, PSNR (peak signal to noise ratio) and RMS (root-mean-square) error data. For a fairly complex image — a fall-colors landscape with significant fine detail in the background tree colors — comparing the perceptually lossless build to a fully lossless build (RGB space), yields a PSNR value of 45.8dB, and RMS error value of 1.3! This clearly illustrates how little loss in quality is associated with perceptually lossless images. For instance, consider the RMS error of 1.3: for 32-bit colors, each rgba component has 8-bits of precision, with values ranging from 0 to 255. For this image, perceptually lossless is introducing an average error of +/-1.3 to these values — fairly negligible for most use cases!!
[While PSNR ratio obviously varies from image to image, I'm seeing ~45dB much of the time]