pnmcolormap

Create quantization color map for a PNM image.

Generate an image using only n_colors or less colors as close as possible to the input image

$ pnmcolormap [n_colors] [path/to/input.pnm] > [path/to/output.ppm]

Use the splitspread strategy for determining the output colors, possibly producing a better result for images with small details

$ pnmcolormap -splitspread [n_colors] [path/to/input.pnm] > [path/to/output.ppm]

Sort the resulting colormap, which is useful for comparing colormaps

$ pnmcolormap -sort [path/to/input.pnm] > [path/to/output.ppm]