Greyscale

Greyscale, or grayscale, is a range of shades of gray that represent the luminance of an image without chromatic information. In digital images, each pixel stores a brightness value, typically ranging from 0 (black) to 255 (white). Greyscale emphasizes lightness and contrast, removing hue and saturation to convey structure and detail.

Converting color to greyscale can use simple averages or perceptually informed algorithms. A common approach is a weighted luminance method that reflects human brightness perception: Y' = 0.299 R + 0.587 G + 0.114 B for standard-definition content. For high-definition content, Rec. 709 weights are used: Y' = 0.2126 R + 0.7152 G + 0.0722 B. Because color channels are nonlinear in typical displays, linearizing RGB values before mixing can improve results. Some pipelines also apply gamma correction or use the luma component of a color space such as Y'CbCr or YUV.

Applications of greyscale include archival imaging, medical X-ray and other scientific imagery, document scanning, and computer vision. Reducing color information can lower data size and simplify processing, while techniques like dithering preserve perceived detail when reducing color depth. Grayscale is also used in printing and film to emphasize texture, contrast, and composition.

In display and printing workflows, greyscale serves as a basic or intermediate representation of visual information. It highlights luminance-related cues that remain interpretable even without color, though it removes chromatic cues that can aid interpretation in some scenes.