Two Kinds of Methods to Extend the Color Gamut of DTV System with Extended Quantization Levels

ITU-R BT.1361 and IEC 61966-2-4(xvYCC) are two standards for video systems with extended-gamut YCC color space, the methods these two standards use to extend the color gamut are not the same. IEC 61966-2-4 put forward that the available quantization levels can be extended to [1, 254] in 8-bit quantization. This paper calculated the value range of luma and chroma signals corresponding to this available quantization range with the colorbar signal which has been widely used in TV system, and put forward two solutions to the problem that the range of extended chroma signals was beyond the conveyable range. One solution was to compress the value and quantization range of extended luma signal in order to make the range of extended chroma signal is exactly within the conveyable range; the other solution was to keep the value and quantization range of luma signal unchanged and use nonlinear(piecewise linear) quantization to process chroma signals. Experimental data with two standards (ITU-R BT.1361 and IEC 61966-2-4) were given out for each solution respectively. Experimental results show that both of the schemes can effectively extend the color gamut with different value of color difference (DeltaE₀₀) and coverage ratio of color gamut. And in the case of compatible transmission with conventional color gamut, both standards can extend the gamut effectively but not significantly, there is still a biggish space for further research on advanced algorithms able to extend color gamut.