Originally Posted by Murilo
My problem is with this statement
"They now have the ability to do both 0-255 and 16-235 levels for RGB over VGA, even though there is no known TV or monitor that expects VGA RGB at 16-235 levels"
I thought 0Ire is 0-255, and and 7.5 IRE is 16-235 but not so.
Unless my flea and microsoft is lying expanded is still 16-235 but 0ire black level. Even that link from microsoft cheif i provided only stated expanded is 0 IRE nothing to do with pc levels. And that other quote I found on the internet stated the xbox and video games output 16-235.
I wish someone could confirm if the xbox does nothing with levels or not.
Let me elaborate a bit. VGA interface consists of 5 signals; R, G, B, H, V. The RGB part I think everyone understands, but what are the H and V? They're horizontal and vertical sync. They're carried completely separately from the RGB color information on a VGA interface. Because sync is carried separately, the RGB output levels use the full range allowed (0-255). If you do not have H and V channels and you combine sync on the green channel (consumer) or sync on all 3 (pro), then you must make accomodation for that by creating a "blanking pedestal" by raising the voltage level during the time when the display should be at black level, from 0 to 16. That way, the TV set can distinguish between black video output (16) and sync level (0). An RGB only interface, with no separate H and V channels, is NOT VGA!
OK now, where does IRE fit into all this? IRE is a term originating in the broadcast industry and it refers to modulation level of the RF transmitter. 0 IRE means 0% modulation and 100 IRE means 100% modulation level. So, when the broadcaster wants to send out video info at black level, the level is set to 16 or 7.5 IRE modulation (roughly 7.5% of 235-16). When the broadcaster wants to send out sync, he sets the level to 0 or 0 IRE modulation. If the broadcaster wants to send out pure white, he sets the level to 235 or 100 IRE modulation. So, when someone says black is at 7.5 IRE, that's 16 on the 0-255 scale. Similarly 100 IRE is at 235 on the 0-255 scale. Of course, all of this is (usually) irrelevant to a full 5 channel RGBHV VGA interface, since there is no need to make room for sync on the RGB channels and the full 0-255 level is used with black = 0 and white = 255. The concept of IRE doesn't figure here, since we're not broadcasting anything. Microsoft, in their infinite wisdom, made this not irrelevant by spitting out 16-235 levels over the full RGBHV VGA interface. I suppose they had difficulty reading the spec. With one of the dashboard updates, they now allow the user to choose between what they call standard (16-235) and expanded (0-255) levels for RGBHV VGA. I stand by my previous statement that there is no known TV or PC monitor that is expecting RGBHV over VGA at 16-235 levels, out of the box. Perhaps there are professional RGB with embedded sync devices out there. I don't know much about SCART and it's use of RGB, but the few references I checked state that sync is not embedded on the RGB channels, but is carried by the composite signal and there is no blanking pedestal. So, I would expect SCART RGB to use the full 0-255 level for RGB.
After the above discussion, it should become obvious that the concept of "expanded" levels (0-255) for YPbPr analog component video, is a contradiction and here again, there are no consumer monitors or TV sets out there that use 0-255 levels for YPbPr component video, since sync is embedded in the Y channel and there would be no way for the monitor to distinguish between sync level and black level. 0 is the lowest voltage level that the DAC can output.
Full digital formats such as YCbCr and RGB over HDMI or DVI, are not limited by the video output DACs and there again, 0-255 levels are the norm for RGB format carried via digital interface. While it is possible to carry 0-255 levels for YCbCr via digital interface, I'm extremely skeptical that there are any consumer monitors or TV sets that expect it. As such, even if the XBOX allows you to set expanded (0-255) levels for YCbCr over HDMI/DVI, the monitor would simply clip anything less than 16, at black and anything over 235, at white. It may not even be possible to recalibrate to correct that.