Extended Data Fig. 7: Visualization of color distribution of slides used in the training and test sets.

In the polar scatter plots, the angle represents the hue (color) while the distance from origin represents the saturation. Each point represents the average hue and saturation of an image after mapping RGB values to optical densities followed by a hue–saturation–density (HSD) color transform. The HSD transform is similar to hue–saturation–value, but corrects for the logarithmic relationship between light intensity and stain amount and has been shown to better represent stained slides^10,32. The training set from a digitized scanner is shown in blue, and test sets from microscopy are shown in red and green.