Fig. 2

Spatial scatter plot of all datasets. The horizontal coordinate is the average of the red-green opposite color intensity channel of each image, and the vertical coordinate is the average of the yellow-blue opposite-color intensity channel. Images were converted from the RGB color space to the Lab color space. The ‘a’ channel represents red-green opposite color intensity; if the positive value is higher, then it is redder, otherwise it is greener. The ‘b’ channel represents the strength of yellow-blue opposite colors; if the positive value is higher, then it is more yellow, otherwise it is bluer. The horizontal coordinate is the average ‘a’ channel of each image, and the vertical coordinate is the average ‘b’ channel.