quality:corruption, information:filtering
Optics

Over the centuries, artists have traditionally created grey by mixing black and white in various proportions. They added a little red to make a warmer grey, or a little blue for a cooler grey. Artists could also make a grey by mixing two complementary colors, such as orange and blue.

Today the grey on televisions, computer displays, and telephones is usually created using the RGB color model. Red, green, and blue light combined at full intensity on the black screen makes white; by lowering the intensity, it is possible to create shades of grey.

In printing, grey is usually obtained with the CMYK color model, using cyan, magenta, yellow, and black. Grey is produced either by using black and white, or by combining equal amounts of cyan, magenta, and yellow. Most greys have a cool or warm cast to them, as the human eye can detect even a minute amount of color saturation. Yellow, orange, and red create a "warm grey". Green, blue, and violet create a "cool grey". When no color is added, the color is "neutral grey", "achromatic grey", or simply "grey". Images consisting wholly of black, white and greys are called monochrome, black-and-white, or greyscale.