Multiprimary Decomposition Method Based on a Three-Dimensional Look-Up Table in Linearized LAB Space for Reproduction of Smooth Tonal Change

Abstract

With the recent development of multiprimary display devices, the three primary colors (red, green, and blue) of a conventional display need to be decomposed into control values for a multiprimary display (MPD) under the constraints of tristimulus matching. To achieve tristimulus matching between such different display systems, the MPD color signals need to be estimated based on a device-independent color space, such as CIEXYZ or CIELAB. Yet, since the focus of a MPD is to display motion picture data, the color space conversion and multiprimary control value decomposition must be simplified. Accordingly, this paper presents a color signal decomposition method for a MPD using a three-dimensional look-up-table (3D LUT) in linearized LAB space. Linearized LAB space satisfies the linearity and additivity required for the color space conversion, and can easily construct a 3D LUT that considers the lightness, chroma, and hue. In addition, to reproduce moving picture data in a MPD, the proposed decomposition method uses a 3D LUT structure to reduce the hardware complexity and processing time. First, a 3D LUT that contains the gamut boundary points of the MPD is created to decompose the multiprimary control values. The chroma and multiprimary color signals for the gamut boundary are then stored in the 3D LUT along with the quantized hue and lightness values. Next, a quadrangular pyramid composed of four gamut boundary points and one lightness point on an achromatic axis is generated according to the input linearized LAB values. Consequently, MPD color signals can be obtained for the input values by interpolating between the multiprimary color signals for the gamut boundary points and the lightness point on an achromatic axis. Furthermore, additional gamut boundary points within 10° of the hue are used to interpolate the input values in regions that involve an abrupt change in the multiprimary control values to achieve a smooth change of hue. As a result, the proposed method guarantees computational efficiency and color signal continuity. Plus, less memory space is required when compared with conventional color decomposition methods.