利用色導表輔助相機測色的精確度評估

Performance of Camera-based Color Measurement using a Reference Color Chart

許凱鈞(Kai-June Xu)；王聖鈞(Sheng-June Wang)；孫沛立(Pei-Li Sun)；江瑞璋(Raymond Chiang)；張輔玲(Fu-Ling Chang)

色彩量測 ； 手機相機 ； 色導表 ； 照明環境 ； 色彩校正 ； 條件等色 ； Color measurement ； mobile phone camera ； color rendering chart ； lighting environment ； color correction ； color metamerism

中華印刷科技年報

2022（2022 / 05 / 01）

1 - 10

繁體中文

本研究之目的在於探討以下問題：（1）手機相機測色直接按色域規格轉換的準確度如何？（2）使用色導表輔助測色的準確度是否能提高？（3）使用不同的迴歸模式校正色彩，是否能提高測色準確度？（4）不同的相機、光源、樣本來源、擺放方式，對測色準確度的影響有多高？。研究結果顯示直接按色域規格轉換的誤差相當大，平均超過10ΔE_(00)，使用色導表輔助測色可使色差降低一倍左右。色彩校正方法以「色差加權高階線性迴歸」最出色。塑膠色樣本由於具有半透明特性，因此需要在XYZ色空間做「漏光增益補償」才能獲得較低的預測色差。在這相機、光源、樣本來源、擺放方式的表現方面，相機的表現各有千秋，四種受測光源下，D65與CWF表現較佳，TL84容易凸顯同色異譜問題，表現最差。三種樣本中，雪面噴墨色差較小，塑膠色差較大。對塑膠而言，平躺的擺放方式比貼背要好。

The purpose of this study is to answer the following questions: (1) How accurate is the color measurement of mobile phone cameras by standard color space conversion? (2) Can the accuracy of color measurement be improved by using a reference color chart? (3) Using different regression modes to correct color, can color measurement accuracy be improved? (4) How much influence do different cameras, light sources, sample types, and placement methods have on the accuracy of color measurement? The experimental results show that the error of direct color space conversion is quite large, with an average of more than 10 Δ E_(00). Using the color chart as a reference to assist color measurement can reduce the color difference to a half. The best color correction method is ＂color difference-weighted high-order linear regression＂. Due to the translucent characteristics of plastic color samples, it is necessary to perform a compensation for ＂light leakage＂ in the XYZ color space to reduce the color differences. In terms of the effects of the camera, light source, sample type, and placement method, the results show that the performance of the cameras varies. Under the four tested light sources, D65 and CWF perform better, while TL84 easily invokes the problem of metamerism and performs the worst. Among the three type of samples, colors of inkjet printing on matte paper are most predictable and stable, whereas colors of plastic samples are most unpredictable. For placing the plastic samples, laying flat is better than sticking to the back in the viewing booth.

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