In visual art, greyscale refers to the exclusive use of shades of grey - i.e. using a palette that consists only of black, white and shades of grey in between.
Examples of greyscale colors:
From an artistic point of view, greyscale emphasizes light and shade, shape, and texture. For this reason, black-and-white photography is popular for artwork that focuses on the beauty of nature or the human body, especially portraits and nude photography.
The greyscale scanning mode
When scanning a black-and-white artwork, such as a pencil or inked drawing, it is often best to set the scanning mode to 'greyscale' or 'color'. Setting it to 'color' will generally result in colors that are not pure greyscale - which can be desired or not. Setting the scanning mode to 'black and white' will usually result in inferior images, even if the original contains no shades of grey, because the lines and edges will lack all anti-aliasing. If a pure greyscale image is desired, the best scanning mode is 'greyscale'.
A color image can be digitally turned into a greyscale picture by changing its color mode, or by applying a filter called desaturation. This filter converts the color of each pixel into a corresponding shade of grey. The hue information is lost in this process and cannot be restored.
The opposite direction, called colorization, is also possible, but requires an artist to manually colorize the image.