Digital Image Processing Glossary

RBG colour

A way of storing the colour information in an image where each pixel's colour is specified by the levels of Red, Blue and Green in that pixel. Each of the three colour channels typically can have a value ranging from 0 to 255.

Lab colour

An alternative way of storing colour information. The three channels for Lab colour are Luminance, 'a' and 'b'. Luminance is akin to brightness. Looking at just the luminance channel of an image shows what the image would look like in black and white. The 'a' channel is a measure on a colour axis that ranges from green to red. The 'b' channel is a colour axis that ranges from blue to yellow.


Gamma is a measure of how dark or light neutral gray should be represented. Setting the graypoint along with the white and black points defines the gamma curve.

unsharp mask

Unsharp mask is probably the most useful sharpening algorithm for digital photography. The unsharp mask searches for regions of rapid change in the image and emphasizes these changes. The effect when done skillfully is to sharpen up the definition between different objects in image.

Would you like to go back to the home page?

Questions or comments?