Color reduction is used to reduce the data volume of color graphics and photos in order to reduce memory requirements and increase the transmission volume. The data volume of color representations essentially depends on the color depth.
For example, a color representation in true- color mode has a color depth of 24 bits, while in high-color mode it has a color depth of 16 bits. 24 bits distinguish between 16,777,216 color tones, whereas with 16 bits only 65,536 color tones can be represented. This means that if a 24-bit graphic is reduced to a 16-bit graphic by means of color reduction, the required memory space has a ratio of 256:1. Further color reductions increase the ratio accordingly.
Since many output devices cannot display such high color depths anyway, on the other hand the differentiation possibilities of the human eye are likewise limited, quality losses by color reductions cannot be perceived as a rule.
One technique of color reduction is dithering, in which different color tones are created by color screening.