t luminance, or brightness, reference white (CIE illuminate D65): GREEN GREEN 1953 NTSC COLOR GAMUT NTSC / PAL/SECAM /HDTV COLOR GAMUT x 560 o 500 YELLOW ORANGE WHITE 780 NM 780 NM PURPLE Figure 7.2-14 CIE 1931 Chromaticity Diagram Showing Various Figure 7.2-15 CIE 1931 Chromaticity Diagram Showing Various Color Regions. Color Gamuts. CHAPTER 7.2 Colour spaces R : =0.630 =0.340 ALL POSSIBLE Y 255, YCBCR VALUES G : =0.310 y = 0.595 CB CR 128 B : 0.155 ==0.070 white : XW = 0.3127 Yw 0.3290 The RGB chromaticities and reference white (CIE illuminate D65) for PAL, SECAM, 576i and 576p video systems are: y, = 0.33 G : : 0.29 yg = 0.60 B : 0.06 white : Xw = 0.3127 Yw = 0.3290 YCBCR VALID The RGB chromaticities and reference white (CIE COLOR BLOCK illuminate D65) for sRGB, scRGB, xvYCC, and HDTV are based on BT.709 and SMPTE 274M: R RED G GREEN B BLUE y, = 0.33 Y YELLOW G : Xg 0 3.30 yg = 0.60 C CYAN M MAGENTA B : xb 0.06 W WHITE white : Xw = 0.3127 Yw = 0.3290 BK BLACK Figure 7.2-16 RGB Limits Transformed into 3-D YCbCr Space. Since different chromaticity and reference white values are used for various video standards, minor color errors may occur when the source and display values do From this illustration it is obvious that there are many not match; for example, displaying a 480i or 480p combinations of Y, Cb, and Cr that result in invalid RGB program on an HDTV, or displaying an HDTV program values; these YCbCr values must be processed SO as to on a NTSC television. These minor color errors can easily generate valid RGB values. Figure 7.2-16 shows the RGB be corrected at the display by using a 3 X 3 matrix normalized limits transformed into the YCbCr color space. multiplier. Best results are obtained using a constant luma and The RGB chromaticities for consumer displays are constant hue approach- is not altered while Cb and Cr usually slightly different from the standards. As a result, are limited to the maximum valid values having the same one or more of the RGB colors are slightly off, such as hue as the invalid co