Color matching functions (CMFs) play a critical role in color science and management. Accurate colorimetry starts with accurate CMFs. Due to changes in the cone pigment optical densities and macular pigment at different retinal locations, different CMFs are required for different fields of view (FOVs). Currently, the CIE 1931 2° CMFs are recommended for a FOV between 1° and 4°, while the CIE 1964 10° CMFs are recommended for a FOV beyond 4°. In 2006, the committee derived a model to estimate the cone fundamentals for normal observers with a FOV ranging from 1° to 10°. With the development of wide color gamut displays and display devices for different application scenarios, several recent studies have disclosed that the field size can have a large impact on CMFs, and hence the colorimetric values are derived from them. It is worth systematically investigating the accuracy and performance of the CMFs recommended by International Commission on illumination (CIE) concerning the parameter of FOVs.

In this study, a series of color matching experiments using spectrally narrowband primaries are performed. Firstly, we select LED panels with red, green, and blue colors of 636 nm, 524 nm, and 448 nm as the target set (named L1 set), and the peak wavelengths of these three primaries are generally similar to those used in Stiles and Burch (i.e., 645.2, 526.3, and 444.4 nm), with wavelength shifts of below 10 nm, which are found to introduce a small degree of observer metamerism. Meanwhile, the L2 (676 nm-524 nm-448 nm) and L4 (636 nm-524 nm-472 nm) are selected as the matched primary sets. Then, three colors including red and blue from the five colors recommended by CIE and white are randomly presented with the L1 target set. After that, forty-five color normal observers are organized to carry out the color matching experiments in four FOVs (2.9°, 5.7°, 8.6°, and 11.0°). Finally, the spectral power distributions (SPDs) of the target and the matched colors are measured immediately.

The SPDs of the target and the matched colors are measured and calculated by CMFs recommended by CIE, including CIE 1931 2°, CIE 1964 10°, and CIE 2006 (1°-10°) CMFs with the indices of color matching accuracy and inter-observer variability ellipses. The Δ(u',v') values are used to test the color matching accuracies, and the results indicate that the CIE 2006 2° CMFs have the best performance in small FOV (below 4°), and the CIE 2006 3° CMFs has the best performance in large FOV (beyond 4°) (Fig. 3). In addition, the chromaticity differences Δ(u',v') with different CIE CMFs between the average chromaticity of three stimuli adjusted by the observers in the four FOVs using the L2 and L4 sets are compared (Table 4). The CIE 1931 2° CMFs have the worst performance in white and red stimuli, while CIE 2006 10 ° CMFs perform the worst in the blue stimulus in the four FOVs. On the whole, the CIE 2006 2°, CIE 2006 3°, and CIE 2006 4° CMFs have the best performances except for the red stimulus in large FOVs and the blue stimulus in small FOV. The 95% confidence ellipses of the chromaticity adjusted by the observers, which are calculated by using different CMFs, are used to express the observer metamerism (Fig. 5). The observer metamerism in small FOV (below 4°) is smaller than that in large FOV(beyond 4°), and the smallest observer metamerism occurs in the white stimulus, followed by the red stimulus, and the blue stimulus has the largest observer metamerism.

This article reports the results of a series of color matching experiments by using narrowband LED primaries under 2.9°, 5.7°, 8.6°, and 11.0° FOVs conditions. In terms of color matching accuracy, the results indicate that in small FOVs, the 2006 2° standard observer CMFs recommended by CIE for small field sizes (below 4°) is confirmed. The results also indicate that among the CIE standard CMFs, the CIE 2006 3° CMFs have a higher predictive performance than the CIE 2006 10° CMFs and CIE 1964 10° CMFs for the field size beyond 4°, which will not support the CIE's recommendation. The CIE 2006 10° CMFs have overestimated the blue cone response in large FOV, which is needed to be improved. In FOV of 2.9°, the color perception tends to be magenta compared with colors matched in large FOV, especially the blue stimulus in the L4 (with the shift of blue primary) primary set. In terms of observer metamerism, a discrepancy of blue cone distribution in retinal occurs among different observers, which will lead to the largest observer metamerism in the blue stimulus, as well as in small FOV (below 4°). With fewer blue cones, the observer metamerism will be smaller than that in large FOV (beyond 4°). The parameters of FOV in CIE 2006 CMFs are needed to be improved and modified when the colors in different displays in the larger FOV are calculated and calibrated.