Colour space & YUV

A device color space simply describes the range of colors, or gamut, that a camera can see, a printer can print, or a monitor can display.

Editing color spaces, on the other hand, such as Adobe RGB or sRGB, are device-independent. They also determine a color range you can work in. Their design allows you to edit images in a controlled, consistent manner.

A device color space is tied to the idiosyncrasies of the device it describes. An editing space, on the other hand, is gray balanced — colors with equal amounts of Red, Green, and Blue appear neutral. Editing spaces also are perceptually uniform; i.e. changes to lightness, hue, or saturation are applied equally to all the colors in the image.

Colorspace is a bit unusual. The Y component determines the brightness of the color (referred to as luminance or luma), while the U and V components determine the color itself (the chroma).

Y ranges from 0 to 1 (or 0 to 255 in digital formats), while U and V range from -0.5 to 0.5 (or -128 to 127 in signed digital form, or 0 to 255 in unsigned form). Some standards further limit the ranges so the out-of-bounds values indicate special information like synchronization.

One neat aspect of YUV is that you can throw out the U and V components and get a grey-scale image. Since the human eye is more responsive to brightness than it is to color, many lossy image compression formats throw away half or more of the samples in the chroma channels to reduce the amount of data to deal with, without severely destroying the image quality.