Originally Posted by chicolom
The xbox 360 uses a piecewise linear approximation of a gamma curve. Is it safe to assume that this is in effect during video playback, such as playing back an AVS HD 709 .mp4 file?
To directly answer your question, no I do not think the piecewise linear approximation (PWL) effect being discussed online has anything to do with video playback. The reason I say this is because I think I have measured how my Xbox plays the video patterns, and I never found significant differences in gamma measurements between my video players. The sorts of differences being discussed with PWL would be expected to clearly show up with measurements if the device was altering video playback.
You would have to ask someone else how exactly the Xbox actually functions regarding differences between games and video playback. On a cursory reading of what Google returns for PWL, I would guess they're primarily talking about something that's game related. From a video playback standpoint, gamma is more a property of the display and really doesn't figure into the sort of video decode expected from a video player. I mean that with video you have gamma correction at the video source (camera) and you expect the display to reproduce along a gamma curve, and where the video player comes into the process you generally don't expect gamma changes. I didn't spend much time reading about PWL and how the Xbox works, but it doesn't make me any less skeptical if video playback on the device happens to match with how games are rendered. The purpose of the video offered here is just calibration for video playback, and I cannot really comment on consoles rendering video games or trying to calibrate for video games.
If you care to read about the basics of how gamma applies to video playback, the following links give a better description of the general process: