Digital Photography and Image Processing
Dithering is a technique used in computer graphics to create the illusion of color depth in images with a limited color palette (color quantization). In a dithered image, colors not available in the palette are approximated by a diffusion of colored pixels from within the available palette. The human eye perceives the diffusion as a mixture of the colors within it (see color vision). Dithered images, particularly those with relatively few colors, can often be distinguished by a characteristic graininess, or speckled appearance.
By its nature, dithering introduces a pattern in to the image, the idea is that the image is viewed from such a distance the pattern is not discernible to the human eye. Unfortunately this is not typically the case and often the patterning is visible. In these circumstances it has been shown that a blue noise dither pattern is the least unsightly and distracting. The error diffusion techniques were some of the first methods to generate blue noise dithering patterns, however, other techniques such as ordered dithering can also generate blue noise dithering without the tendency to degenerate in to areas with artefacts.
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