pixmap

As nouns the difference between pixmap and null

is that pixmap is a grid of pixels while null is a non-existent or empty value or set of values.

As an adjective null is

having no validity, "null and void.

As a verb null is

to nullify; to annul.

As nouns the difference between taxonomy and pixmap

is that taxonomy is the science or the technique used to make a classification while pixmap is (computer graphics) a grid of pixels.