Figure 5.

Histogram matching with and without a subfeature. Top left: The reference histogram. Top right: The input histogram. Bottom left: The histogram using conventional HM. Bottom right: The histogram after HM with subfeature. Conventional HM has to move the pixels with the same intensity as a group and, therefore, results in the quantization and rounding-off errors, which can be observed as the spiky artifacts on the processed histogram as indicated by the green arrows in the bottom left figure. The errors can be reduced with the subfeature, which enables us to separate pixels with the same intensity but in different retinal layers, as shown in the bottom right figure. The red curve in the bottom left and bottom right figures presents the shape of the reference histogram.