白光LED與日光頻譜差異對相機色彩校正的影響

Influence of Spectrum Difference Between White LED and Daylight on Camera Color Correction

本研究之目的在於探討光源不匹配對相機色彩校正準確度的影響。本研究以CIED65為預設的色彩校正環境，以色溫相近的CIE LED-B5為不匹配的光源。為此，本研究建構了一台虛擬相機，評估在預設的D65色彩校正模式下，TCS99色樣本分別在D65與LED-B5光源下拍攝的色彩準確度。研究結果顯示，當相機拍攝環境與校正環境相異，色差會提高。相較於D65，色溫相近的白光LED會稍微提高黃藍色的彩度，降低紅綠色的彩度。額外的二階迴歸修正，不但能有效降低拍攝環境與校正環境相異造成的色差，對環境相同的組合，也能明顯的降低色差。這可能是由於一般相機的色彩校正僅使用24色ColorChecker對3×3的色彩校正矩陣迴歸，這麼少的樣本數與迴歸的參數量，難以描述TCS99色樣本的色彩特性。

The purpose of this study is to investigate the effect of light source mismatch on the accuracy of camera color correction. In this study, CIE D65 was used as the default color correction environment, and CIE LED-B5 with a similar color temperature was used as the unmatched light source. To this end, this study created a virtual camera to evaluate the color accuracy of TCS99 color samples shot under D65 and LED-B5 light sources under the default D65 color correction mode. The experimental results show that when the camera shooting environment is different from the correction environment, the color accuracy will decrease. Compared with D65, white LEDs with similar color temperature will slightly increase the chroma of yellow and blue, and reduce the chroma of red and green. The additional second-order regression correction can not only effectively reduce the color errors caused by the difference between the shooting environment and the calibration environment, but also significantly reduce the color errors for the same environment combination. This may be because the color correction of general cameras only uses 24-patch ColorChecker to optimize the 3×3 color correction matrix. With such few samples and regression parameters, it is difficult to describe the color characteristics of TCS99 color samples.