Real-Time Color Matching Between Camera and LCD Based on 16-bit Lookup Table Design in Mobile Phone

摘要

Based on the concept of multimedia convergence, imaging devices, such as cameras, liquid crystal displays (LCDs), and beam projectors, are now built-in to mobile phones. As such, mobile cameras capture still images or moving pictures, then store them as digital files, making it possible for users to replay moving pictures and review captured still images. Increasingly, users want LCD in the mobile phone (we call it mobile LCD hereafter) to reproduce the same colors as the real scene. Accordingly, this paper proposes a method for color matching between mobile camera and mobile LCD that includes characterizing the mobile camera and mobile LCD, gamut mapping, camera noise reduction, and a 16-bit lookup table (LUT) design. First, to estimate the CIELAB values for the objects in the real scene, mobile camera characterization is achieved through polynomial regression of the optimal order determined by investigating the relation between captured RGB values and measured CIELAB values for a standard color chart. Thereafter, mobile LCD characterization is conducted based on 16-bit/pixel processing because of the reduced bit depth of the images displayed on a mobile LCD. In addition, a sigmoid model is used to find the luminance value corresponding to the RGB control signal, instead of using gain offset gamma and S-curve models due to the adjustment of luminance curve made by a system designer for preference color reproduction. After completing the two types of characterization, gamut mapping is performed to connect the source medium (mobile camera) with the target medium (mobile LCD), then a combination of sigmoid functions with different parameters to control the shape is applied to the luminance component of the gamut-mapped CIELAB values to reduce camera noise. Finally, a three-dimensional RGB LUT is constructed using 16-bit/pixel-based data to enable color matching for moving pictures and inserted into the mobile phone. Experimental results show that moving pictures transmitted by a mobile camera can be realistically reproduced on a mobile LCD without any additional computation or memory burden.