Research On Gamut Expansion Of Laser Display

Laser display is a new type of wide gamut display technology, the primaries of which are red, green and blue laser. The color gamut of laser display can cover70%of nature color, and1.8times wider than NTSC standard, so it can show very rich and colorful colors. Because the gamut of laser display is different with that of current standards, the existing standard image signal cannot be applied to laser display directly. In order to make the laser display compatible with the existing image signal, and fully show the advantage of wide gamut, gamut extension mapping from standard gamut to the laser gamut turn to be one of the necessary process and key technology for laser display, thus the research on gamut extension for laser display has important theory significance and high practical value.This paper mainly focuses on the gamut expansion research of standard gamut to the laser display gamut and the related hardware implementation. One evaluation method of gamut expansion algorithm and two color gamut expansion methods are proposed.With color gamut expansion experiment of a large number of pictures, the result shows that increasing the saturation of the human eye sensitive color, e.g. the skin color, will cause the problem of "excessive rendering" and the large coefficient gamut expansion to small range will cause the stepped-block color problem. These two issues will turn the result of image mapping to worse situation, so these two problems can be the indicatrix of gamut expansion evaluation and any color gamut expansion algorithm should avoid the two problems above.On the basis of the existing algorithms, this paper raises a multilevel gamut expansion method, which includes the Hue-Varying Nonlinear Expansion (HVNE) algorithm and Image Depended Chrominance Smoothing (IDCS) algorithm.HVNE algorithm adopts mutative extension function with the change of hue which is divided into the non-linear expansion region, the transition region and the linear expansion region three parts. Using "static" color similarity function, the human eye sensitive color belongs to non-linear expansion region, the critical color around the human sensitive color is part of the transition region, and the else falls into linear region. The algorithm combines the advantage of linear expansion and nonlinear expansion algorithms, and avoids "excessive rendering" problem by nonlinear expansion and stepped-block color problem by linear expansion, and the mapping image have better visual effects compared with existing algorithms.Generally, gamut expansion method needs gamut boundary calculation, as most of the existing algorithms are computationally costly, a gamut boundary calculation algorithm based on center of triangle surface is proposed. The algorithm uses space angle of triangle surface and objective point to accelerate the speed of tetrahedron matching. The experimental result shows that, this algorithm can reduce40%of calculation time of existing method, and computational time only increases a little when adding the number of sampling points.The practical value of the gamut expansion algorithm is determined by the hardware implementation cost of the algorithm, In order to simplify the complexity of the gamut expansion algorithm and reduce the costs for hardware realization, this paper puts forward a gamut extension algorithm based on RGB Space, and describes the hardware architecture of the algorithm. The proposed algorithm is based on the hue-preserving transformation of RGB space, and, firstly, converts the image signal form RGB space of standard gamut to that of laser gamut, then enhances the chroma of color with the ratio of the two gamut boundaries as the expansion coefficient and the saturation of color. With the gamut expansion experiment of a large number of pictures and FPGA-based verification results show that, the proposed algorithm has good image gamut expansion result, and avoids the "excessive rendering" problem, and needs less logic resources which indicates low-cost advantage.