A feature is nothing magical. It is simply a number that we computed from an image. There are several feature sets already defined in literature. These often have the added advantage that they have been designed and studied to be invariant to many unimportant factors. For example, linear binary patterns are completely invariant to multiplying all pixel values by a number or adding a constant to all these values. This makes this feature set robust against illumination changes.
However, it is also possible that your particular use case would benefit from a few specially designed features.
A simple type of feature that is not shipped with mahotas is a color histogram. Fortunately, this feature is easy to implement. A color histogram partitions the color space into a set of bins, and then counts how many pixels fall into each of the bins.
The images are in...
