Illumination Estimation Based on Valid Pixel Selection from CCD Camera Response

This article proposes a method for estimating the illuminant chromaticity using the distributions of the camera responses ob- tained by a CCD camera in a real world scene. Illumination estimation using a highlight method is based on the geometric relation between a body and its surface reflection. In general, the pixels in a highlight region are affected by an illuminant geometric difference, camera quantization errors, and the non-uniformity of the CCD sensor. As such, this leads to inaccurate results if an illuminant chromaticity is estimated using the pixels of a CCD camera without any preprocessing. Accordingly, to solve this problem, the proposed method analyzes the distribution of the CCD camera responses and selects pixels by the Mahalanobis distance in highlight regions. The use of the Mahalanobis distance based on the camera responses enables the adaptive selection of valid pixels among the pixels distributed in the highlight regions. A principal component analysis (PCA) is then used to determine the lines based on the r − g chromaticity coordinates of the selected pixels. Thereafter the illuminant chromaticity is estimated based on the intersection points of the lines. Experimental results using the proposed method demon- strated a reduced estimation error compared with conventional methods.