This method consists of two stages and one post-processing step, i.e., the calibration stage, the test stage, and the selection step. In the calibration stage, as shown in Fig. 1, we first calculate the system matrix and initial Wiener matrix using the calibration data, which contain both measured RGB color values and the corresponding measured diffuse reflectance spectra. The estimation of the system matrix is an overdetermined problem and thus should be accurate because a diffuse reflectance spectrum contains many more data points than RGB values. Diffuse reflectance spectra can be estimated from measured RGB color values by using the initial Wiener matrix. Then, by applying a synthetic absorption filter, which contains three absorption bands different from RGB filters, to the system matrix, a modified system matrix can be created, which is used to generate two separate sets of three new color values from the measured and estimated diffuse reflectance spectra. The transmission spectra of the three synthetic absorption filters were determined by Gaussian functions with different center wavelengths: 500, 550, and 600 nm, and a standard deviation of 100 nm. The center wavelengths were selected to deviate from those of RGB filters in order to cover different information. Because of the high accuracy of the system matrix, the new color values estimated from the measured diffuse reflectance spectrum should be accurate and thus could be seen as the reference new color values. The new color values generated from the estimated diffuse reflectance spectra are less accurate, which will be called estimated new color values to facilitate the discussion next. The relation between the estimated new color values and the reference new color values can be found by using the following two strategies: 1. to model each reference new color value as a second-order polynomial function of estimated new color values; 2. to record the differences in each color value between two sets. Moreover, the reference new color values combined with the original RGB values are used to create a modified Wiener matrix for the second-round estimation of diffuse reflectance spectra in the test stage, which will be more accurate than using the RGB values alone because of the increase in the number of available color bands.