Color Reproduction Characteristics of Liquid Crystal Display Panels and New Compensation Methods for Them

The color reproduction characteristics of LCD (liquid crystal display) panels are different from those of CRT (cathode ray tube) displays. This paper describes how the authors measured and analyzed such characteristics of LCD panels to develop new methods for compensating the bluish cast found on conventional LCDs. The first one is a hardware-based technique that employs a LUT (look-up table) and the second a software-based color management technique utilizing ICC profiles compensating the bluish cast. The authors achieved faithful color reproduction for standard sRGB with both methods. Introduction Many aspects are examined in evaluating the image display characteristics of a liquid crystal display (LCD) panel, including brightness, viewing angle, contrast, color reproduction, and gamma characteristics. Subjective evaluations of the color reproductions of LCD panels reveal they have superior rendition of the blue color system, and are highly rated for their ability to display the blue of the sky, as memory colors readily recalled by human beings. Nevertheless, an LCD's color reproduction differs from sRGB color space, the standard color space used on the Internet, and thus the color reproductions of LCD panels must be made to coincide with the standard sRGB color reproductions. For example, in selling over the Internet (e-commerce), color matching is important for fashion accessories, home furnishings, and the like. Thus, it is desirable that LCD panels not only provide pleasing color reproduction, but that they have the capability to faithfully reproduce standard sRGB color. We developed two methods to compensate for the unique color reproduction characteristics of LCD panels to achieve standard color reproduction: 1) Compensate by interposing a hardware look-up table (LUT) between the input image signal and the display panel, and 2) Compensate using software-based ICC profiles. The color reproduction characteristics of LCDs and compensation methods for them are described below. 1. Color reproduction characteristics of color LCD panels It is not surprising that LCD panels have unique color reproduction characteristics which differ from those of CRT (cathode ray tube) displays, because of the difference in the principles used to display color. Fig. 1 shows an x-y chromaticity diagram resulting from measuring the color reproduction characteristics of a typical transmissive TFT color LCD (Sharp LL-T1510A). The color reproduction characteristics were measured by generating a color patch on the display and using a luminance colorimeter (Topcon BM-5A) to Color Reproduction Characteristics of Liquid Crystal Display Panels and New Compensation Methods for Them Yukio Okano Nozomu Shiotani * Interface Development, System Technology Development Center, Corporate Research and Development Group