Those who have ever made the costly mistake of filling up with the wrong kind of fuel can personally describe the rough, shaking ride they endured when the fuel started to circulate in the car. Poor camera quality and extreme color and saturation adjustments also create a “rough ride” from one color to another within the image. That rough ride is called Posterization.
Generally, within photos, the transitions from one color to another are imperceptible because there are thousands or even millions of different shades to make the change gradual and natural. However, in images with posterization problems, these changes are not gradual, but “jump” from one color to another. This usually happens in the areas of the image with little detail, such as the sky, producing the appearance of distinct bands of color. It occurs in areas with a limited range of color tones, and appears as brusque, unnatural transitions from color to color. This is also frequently caused by drastic color adjustments during digital post-production, for example when you “force” a curve (create an extreme curve) or saturate the image in excess.
Here is an example of posterization:
Example. In the enlargement on the right, notice how the woman’s hair changes abruptly from the light to the dark zone. That part of the image is missing the tones it needs to accurately show the colors in the woman’s hair. This problem affects the color transitions throughout the entire image.