1、STD-ITU-R RECMN BT*33bL-ENGL 1998 4855232 0534B04 YO4 319 RECOMMENDATION ITU-R BT. 136 1 WORLDWIDE UNIFIED COLORIMETRY AND RELATED CHARACTERISTICS OF FUTURE TELEVISION AND IMAGING SYSTEMS (Question ITU-R 1-3/1 1) (1 998) The ITU Radiocommunication Assembly, considering that colorimetric parameters v
2、ary among existing television systems; that computer graphics are finding application in television programme production, while that interoperability between different television systems and other imaging systems such as that unified colorimetry is desirable for interoperability to minimize conversi
3、on between that although existing television displays can reproduce a large proportion of the colours a b) television displays are used with computers; c a motion picture film and computer graphics is required; d) different television systems and imaging systems; e contained in natural scenes, a wid
4、er colour gamut is required to reproduce all natural surface colours; f) g cost and performance; h) system provides full colour information, and should not be limited by the reproducible gamut on a particular display; j that the colour gamut of a system can be extended by allowing negative and great
5、er than 100% RGB signal values, while maintaining compatibility with conventional systems; k) that while colorimetric parameters and related characteristics have been specified for conventional colour gamut in Recommendation ITU-R BT.709, and for conventional and extended colour gamut in Recommendat
6、ion ITU-R BT. 1200, a single Recommendation specifying a unique set of colorimetric parameters and related characteristics is required for all future television systems; 1) that the adoption of a worldwide unique set of colorimetric parameters and related characteristics will assist in developing ef
7、ficiencies in international exchange and spectrally efficient unified transmission systems; m) that the adoption of a worldwide unique set of colorimetric parameters and related characteristics will ultimately result in economic benefits for broadcasters and the broadcastreceiver industry, this in t
8、urn will assist organizations operating within countries having developing economies, that new display devices capable of reproducing a wider colour gamut are being introduced; that the reproducible colour gamut may vary between displays by reason of application, that in selecting colorimetric param
9、eters of a television system, it is essential that the STD-ITU-R RECHN BT-L3bL-ENGL 1978 W 4855212 0534805 340 320 Green Blue D65 recommends 0.300 0.600 O. 150 0.060 Chromaticity coordinates (CIE 193 1) X Y 0.3 127 0.3290 1 and Table 3 of this Recommendation be used for all fture television and imag
10、ing systems. that the colorimetric parameters and related characteristics as described in Table 1, Table 2 TABLE 1 Colorimetric parameters and related characteristics Parameter 1 Primary colours 2 Reference white (equal primary signal) 3 Opto-electronic transfer characteristics() Values Chromaticity
11、 coordinates (CIE 193 1) X Y Red I 0.640 I 0.330 I E = 1.099. - 0.099 for 0.018 si M e O cd E: ce .d .3 m ._ .- Y - 2 2 - W .- Ld W o I -3 W ta -!c 4 3 a m , h STD-ITU-R RECMN BT.13bL-ENGL 1998 = q655212 0534808 05T 323 ANNEX 1 Extended colour gamut system using negative RGB signais The reproducible
12、 colour gamut on a television display is limited to that area inside a triangle on the chromaticity diagram composed of the three primary colours of the display. This is due to the fact that negative light emissions of the primary colours cannot be realized with an actual display system. However, co
13、lours outside the triangle can be transmitted when negative and greater than 100% values are allowed as extended primary RGB signals. Current cameras normally develop extended gamut RGB signals in the process of linear matrixing to optimize colorimetric analysis, but the extended values are usually
14、clipped in the subsequent processes to conform to the signal format of the system. The colour gamut extension method using negative RGB signals provides compatibility with conventional systems, resulting in a smooth transition to the new wide gamut system. Signal range The required signal range of a
15、 television system is determined by reference primaries, opto-electronic transfer characteristics (gamma curve), and the colour gamut to be handled by the system. An exceptional signal range is required to reproduce the full range of pure spectral colours even with a wide gamut set of primaries. A r
16、ealistic approach is to limit reproduction to the gamut of real surface colours as determined by Pointer. Levels of analogue gamma pre-corrected RGB signals for the Pointer colours are shown in Figure 1 (a)-(c). The Pointer colours provide the most highly saturated real surface colours for 36 hues (
17、every 1 O degrees) and 16 lightness levels. In the figure, 16 curves are drawn for different lightness levels, and it can be seen that these RGB signals exhibit negative and greater than 100% values. When these analogue RGB signals are converted into analogue luminance and colour difference signals
18、using Equations 4, Table 2, the resulting levels are shown in Figure 2 (a)-(c). It can be seen that the levels are now contained within the normal dynamic range of O - 100% for luminance and h50% for colour difference. Thus for analogue signals there is a direct compatibility between conventional ga
19、mut systems and the equivalent colours in an extended gamut system. For digital representation, it is necessary when quantizing extended gamut RGB signals to use different scaling factors and DC offset from those used for conventional gamut, as shown by Equations 5, Table 3, i.e. 160 and 48 instead
20、of 219 and 16. This is because the levels of the gamma pre-corrected extended gamut RGB signals exceed the dynamic range specified in Recommendations ITU-R BT.601 and BT.1120, indicated by the dashed lines in Figure 1 (a)-(c). However, as with the analogue signals, quantized luminance and colour dif
21、ference signals for conventional gamut and extended gamut are both accommodated within the dynamic ranges specified in Recommendations ITU-R BT.601 and ITU-R BT.1120, as indicated by the dashed in Figure 2 (a)-(c). It follows that for compatibility, conversion from quantized RGB signals to quantized
22、 luminance and colour difference signals require different scaling factors as shown by Equations 6, Table 3. ines BIBLIOGRAPHY KUMADA, J. and NISHIZAWA, T. - “Reproducible colour gamut of television systems”, SMPTE Journal, Vol. 101, No. 8, pp. 559-567, August 1992. POINTER, M.R. - “The gamut of rea
23、l surface colours”, Colour Research and Application, 5, pp. 145-155, John Wiley Step 2: With the initial integer coefficients, calculate the r.m.s. errors or the squared difference sum (Equation (10) over the input RGB signal range, e.g., 16 through 235 for an 8-bit system (a simple calculation meth
24、od without using summation is described in Section 1.3); Step 3: Examine the r.m.s. errors when increasing/decreasing each integer coefficient by one. 27 (=33 ) combinations must be evaluated in total, because each coefficient can take three values, i.e. increased, decreased and unchanged from the i
25、nitial value. Step 4: Select the combination of the coefficients that gives the minimum r.m.s. error. This combination is the resultant optimized one. The same procedure is applied for the colour-difference equations, using Equations (1 1) and (12). 1.3 By expressing the difference between integer a
26、nd real coefficients value as 6, = kg - rg, and the digital RGB signals as 3, the sum of the squared differences of Equations (1 O) - (1 2) can be written as the following: Simple calculation method for squared difference sum ,HHH xi =LX2=L X3=L L where L and H denote the lower and upper boundaries
27、of the input signal range, respectively, for which the integer coefficients are to be optimized. As L and H are constant in the digital system under consideration, the summations for XJ are also constant. Then Equation (1 3) can be expressed as a function only of 6,. where: H HIH H HfH H HfH = - L +
28、 lp -(H +IX2H + 1)/6 - (L - 1)L(2i - 1)/6) N2= 5 5 5x4 = 5 i 5X2X3 = 5 i ,X,Xj x3 =L x1 =L x, =L xj=L X2=LX3=L X2=L X3=L x1= L = - L + I)(H + I)/ 2 - (L - 1)L / 2 y Thus the calculation of r.m.s. errors or Equations (10) - (12) can be simply performed by Equation (1 4). STD-ITU-R RECMN BT.13bL-ENGL
29、1778 m Li855212 053Li815 27T m 330 2 Extended colour gamut system 2.1 Digital equations The digital luminance equation for the extended colour gamut system is described as follows: +0.7152 +om2 D“8)-482“-8 160 +16.2n-8 where Y“ and k“ denote real values of the coefficient and integer coefficients, r
30、espectively, given below. 219 160 0.2126 x - x2“ 219 2m rlY = O. 0722 x - 160 klY2 = INT rlY2 k“y3 = INT “y3 klY4 = INT rly4 The digital colour-difference equations for the extended colour gamut system are described as follows: - - -0.2126DR -0.7152 DIr +0.9278 DI, 224 +2n-l 1.8556 160 Dc, = INT 1 0
31、.7874 D“, -0.71520“, -0.0722D1, 224 x - + 2“- I. 5748 160 DIcR = INT where: 0.9278 224 1.8556 160 rICB3 = - x - x 2“ 0.7874 224 1.5748 160 r“CR1 = - x - x 2“ 0.7152 224 1.5748 160 r“cR2=- x- x2“ 0.0722 224 1.5748 160 r“CRJ=- x- x2m 2.2 Optimization procedure The optimization procedure is the same as
32、 that for the conventional colour gamut system, using Equations (24) - (26). Note that for the luminance equation, the number of combinations to be evaluated for the r.m.s. error becomes 8 1 (= 34) instead of 27, because there are four coefficients to be optimized. 2.3 Similarly to the conventional
33、colour gamut system, Equation (27) is obtained for the luminance equation of the extended colow gamut system. Simple calculation method for squared difference sum ,HHH “ x,= LX2 =L XJ =L L 1 =- (6:1 +G, +6$3)+2N2 (6,6,2 +8Y26Y3 +6Y36Y1)+2N3 (h +6Y2 +6Y3)6Y4 +46:,) (27) 2m where NI and N2 are given i
34、n Equation (14), and = -L+lpp(H+1)12-(L-l)L/2) 332 STD-ITU-R RECMN BT-13bl-ENGL 1776 D Lib55212 053V817 Ob2 HHH N4=C c x1 =L X2=L x3= L =-L+i)3 For the colour-difference equations, the same equation as that for the conventional colour gamut system (Equation (1 4) is applied. 3 Optimized integer coef
35、ficients The resultant optimized integer coefficients are listed below for the coefficient bit-lengths of 8 - 16. TABLE Al Optimized integer coefficients for conventional colour gamut system STDOITU-R RECMN BT*33bl-ENGL 1798 W 4855232 053B3B TT7 333 TABLE A2 Optimized integer coefficients for extend
36、ed colour gamut system NOTE 1 - The value of k”y4 depends on the signal bit-lengths yi, and the values listed are those for the cases m = n. It is confirmed that the optimized values are identical with the initial nearest integers in m + n bits precision, when m and y1 are within 8 - 16. NOTE 2 - Th
37、e underlined italic indicates the values modified from the initial nearest integer by the optimization. NOTE 3 - For the conventional colour gamut system, the RGB signal region used in the optimization is the nominal signal range of Recommendation ITU-R BT.601 and its extensions, i.e. the range 16 x 2n-8 -235 x 2n-8 for an n-bit system. For the extended colour gamut system, it is the maximum signal range of Recommendation ITU-R BT.601 and its extensions, i.e. 1 x 2n-8 -254 x 2n-8.
