Hello, Mike Tsinberg wrote: Ø No, common mistake created by marketing. And you thought that you should add to the confusion ? ;-) Ø Both current HDTV (rec 709) and xvYCC are 8 bit systems. Ø The color gamut for HDTV, of each Red, Green and Blue colors is designed within BT.709 standard for 16 to 236 level systems or 220 quantization levels. 16 to 236 is a legacy issue for component YCrCb. It's 16..235 for Y' and 16..240 for Cb,Cr. And it's not a legacy issue, it is an inherent necessity for proper sampling and reconstruction. These are the reference levels for nominal black and white, i.e. for large areas. The other levels are used for the overshoots and undershoots that occur during proper anti-aliasing filtering. A filter without ringing would have too little bandwidth. You can't have proper (smooth) motion portrayal without anti-aliasing. If you cut off the over- and undershoots in order to limit the range, then that clipping is a non-linear operation and it will cause aliasing. There will be jittering and flickering on all sharp moving edges. Of course somewhere in the video path we still have to get rid of these extra levels, particularly the below-black levels. Traditionally this was done --after reconstruction-- in the analog time- continuous domain, where clipping will not cause aliasing anymore. Clipping off the overshoot was not necessary, as CRTs could handle the peak white. With digital pixelated displays this becomes a different story. Then the only solution seems to be that the spectrum at the display be not too full, i.e. an oversampled display or an underutilized transmission channel. Neither seem to be attractive. It helps that full-HD is already a bit better than we really need, so indeed we see much smoother motion with HDTV. I find this very pleasing. Ø A fully digital interface, such as HDMI, is capable of a full 0 to 255 performance without increasing the 8 bits per color specification. This is a common mistake created by the computer community. As in the beginning they were dealing only with static images, or perhaps images that move only in discrete speeds of multiple pixels per frame, aliasing was not yet an issue. Also, since most of the chain was still analog (CRT !) it was common to calibrate the black and white levels in the analog domain (potmeters in the CRT monitor). With an all-digital chain you need some headroom and footroom for calibration. It's not wise to use the full (8-bits) range for your signal over the entire chain. Ø The xvYCC is a new color gamut standard that uses the full range of values from Ø 0 to 255 or 256 quantization levels in an 8-bit space to represent colors. I included a Ø picture of color space comparison. Technically the levels Y' = 0 and Y' = 255 are probably still illegal, as they are reserved for synchronisation. Besides that, the illustration is plain wrong. Even the co-ordinates for the Rec.709 primaries are very very wrong. And the color space of xvYCC can not even be described as a simple triangle in (x,y) space. It depends on the luminance. If you combine a low value for Y' with large absolute values for Cb,Cr then the color space is even infinite. Or at least it goes way beyond the visible colors. Katoh and I have illustrated it nicely during our presentations at the HPA Tech Retreat 2007. I suggest that you look it up. Essentially the extension of the xvYCC color space relative to Rec.709 has two parts: - formally illegal combinations of legal Y'CbCr values that will lead to R'G'B' values that are < 0 or > 1, which I like to call wide-gamut c.q. bright-gamut colors, and - all combinations of formerly illegal Y'CbCr values, that will lead to even more extreme R'G'B' values. It's only the latter colors, typically very bright colors, that eat into the space that should have been reserved for ringing (anti-aliasing). Typically they represent fluorescent objects or light sources. Yes, this does allow a bit more "sparkle" in the picture, but they are not so relevant to the wide-gamut issue. They can be avoided by proper scaling of the signal range. Ø Deep color increases bit depth from 24 bits per pixel (8 bit per color) to 36 bits (12 bit per color). Either 709 or xvYCC can be used with deep color. Perhaps "deep color" is misleading. It should be called probably "accurate or deep gray" or something. Correct about the meaning of deep color. It is my opinion that a video chain allows only one 8-bit bottleneck, and then only if the original signal comes with enough (analog ?!) noise to dither away the quantisation error of the 8-bit quantizer. If there are multiple processing steps with multiple 8-bit bottleneck between them, then the quantisation noise will soon be unacceptable. Therefore, every interface that can be upgraded to more than 8-bits is very welcome. Internal interfaces (i.e. on a chip or on a PCB) are easy. The external HDMI interface was a logical candidate for an upgrade of the standerd. It used to be that contrast control was in the analog domain (again: CRT), so the video path before that had a constant amplitude and 8-bits would do. Now that everything has been moved to the digital domain, we need more precision at the display input. That picture is changing again with the introduction of backlight dimming, where extra bits can be carried over the backlight intensity signal. And it will be changing again with the introduction of High Dynamic Range signals and displays, where an entire intensity map (of low resolution) will be carried in parallel with the video path. But most likely these signals will not be separated over the HDMI interface, so it is there that a high precision will remain essential for a combined HDR signal. By the way... HDMI has always been capable of 12-bits precision. That's because it re-uses the hardware of the DVI interface, which can do 8-bits R'G'B'. HDMI can do (also) Y'CbCr 4:2:2, and with 12-bits components this also adds up to an average of 24 bits per pixel. It costs nothing ! The "deep color" extension means that this can also be enabled for 4:4:4 components, but at the cost of more bits per second over the link. Groeten, -- Jeroen Jeroen H. Stessen Specialist Picture Quality Philips Consumer Lifestyle Advanced Technology (Eindhoven) High Tech Campus 37 - room 8.042 5656 AE Eindhoven - Nederland Office mobex: (27) 99650 VoipBuster: +31.85.785.3611 (VoIP-in to PC) Mobile 1: +31.6.1389.2492 (office gsm) Mobile 2: +31.6.4468.0021 (personal gsm) E-mail 1: Jeroen.Stessen@xxxxxxxxxxx<mailto:Jeroen.Stessen@xxxxxxxxxxx> E-mail 2: Jeroen.Stessen@xxxxxxxxxx<mailto:Jeroen.Stessen@xxxxxxxxxx> Website: www.consumer.philips.com<http://www.consumer.philips.com> ________________________________ The information contained in this message may be confidential and legally protected under applicable law. 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