Calibration of Illumination Loss to Measure Luminance and Chromaticity Distribution by Using Digital Camera

It is required to obtain chromaticity and luminance distribution of the natural scene with a digital camera. One of the problem to measure with the digital camera is that it has low dynamic range. The purpose of this study is to derive relational expressions between pixel values of several images with different exposure times and chromaticity or luminance. The prediction functions are derived by using the multiple regression analysis from XYZ obtained by measured values and pixel values (log10Y=αR+βG+γB+δ(Δt)). The coefficients of RGB of the prediction function were constant regardless of exposure time, in contrast, the δ value was represented by the exposure time function. Therefore, the prediction function moves parallel by the exposure times. The error between the actual measurement values and the predictive values were 8%, 6%, 5% in X,Y,Z. Therefore, it was able to acquire the chromaticity and the luminance distribution with a digital camera. There is problem that amount of light of the surrounding imaging area decreases more than center imaging area actual measured values. We construct a model of calibrate prediction function by the eccentricity from damping rate of the center of the lens.