What Does Posterization Mean When Talking About Photography and Image Editing?

In photography and image editing unwanted posterization, also referred to as banding, occurs when the bit-depth of an image is lowered enough to have a negative impact on an image. posterization can be caused by any process which ‘stretches’ an images histogram for example applying excessive compression. Posterization gets it’s name from its visual effect on an image; Distinct bands of individual colour will appear which make it look like the image has been converted into an old fashioned graphic poster. Another tell-tale sign of posterization can be spotted in an images RGB histogram, which will display distinct spikes when posterization is occurring.