Chrominance is the distinction between adjacent colors, and chrominance quality affects the sharpness of this distinction. The colors in an image with a very low chrominance quality may appear smeared. For example, an image that contains a red house with a blue sky in the background may appear as a red house surrounded by a red sky that gradually fades to blue farther away from the house.
The following background options specify an image’s chrominance quality:
--crcbnormal – Sets a normal level of chrominance quality (default). Chrominance information is encoded at the same resolution as the luminance, making the blurring of colors unnoticeable unless you magnify the image. Some blurring, however, does occur to significantly reduce the size of the encoded image file.
--crcbhalf – Sets a half-resolution chrominance quality. Chrominance information is encoded at half the luminance resolution. Colors blur slightly, but if the colors in your image are consistently the same, such as a blue sky over a blue ocean, you will not notice the blurring. The primary advantage of this option is that it significantly reduces the size of the encoded image file.
--crcbfull – Sets a maximum level of chrominance quality. This option is the equivalent of specifying both --crcbnormal and crcbdelay=0. Colors do not blend together even when the image is magnified; however, the size of the encoded image file may increase.
--crcbnone – Removes all chrominance information and only luminance information is encoded. The effect is the same as converting the file to grayscale.
--crcbdelay=<1-32> – Sets the chrominance delay factor to influence blurring and file size. Unlike the other chrominance quality options which affect all objects, however, --crcbdelay affects only small objects. A value of 1 produces the best quality and the largest file size. The default for this option is 16.
Supporting commands:
documenttodjvu, phototodjvu