In the context of images, a greyscale colour model represents a picture using only shades of grey, from pure black to pure white. There’s no colour information included. This is commonly used in black-and-white photography or to convert colour images into black and white.
- The greyscale colour model is used for:
- Converting colour images to black-and-white.
- Creating black-and-white images through cameras, scanners, and other input devices.
- Three algorithms are commonly used for greyscale conversion: the lightness method, the weighted average method, and the luminosity method.
- The greyscale colour model is not a simple linear scale from black to white but rather a method of converting colour brightness to reflect tonal relationships. When converting digital images to greyscale, each pixel is assigned a corresponding level of brightness based on its colour.
- When fully saturated spectral colours are converted to greyscale, their brightness typically ranges between 11% and 89%. For example:
- Red = 70%
- Orange = 40.38%
- Yellow = 11%
- Green = 41%
- Blue = 89%
- Violet = 74.06%
- Any RGB decimal colour value can be converted to greyscale. For instance, the RGB value for cyan converts to a greyscale value of 178, 178, 178. Similarly, HSB colour values can also be converted to greyscale, with the HSB value for pure yellow being Hue = 0, Saturation = 0, and Brightness = 11%.