grayscale

Grayscale is a range of shades from black to white that represents image luminance without hue. In a grayscale image, each pixel corresponds to a single intensity level rather than a color triplet, producing a spectrum of gray tones from pure black to pure white.

Digital grayscale images are typically stored with a single channel, with common bit depths of 8, 12, or 16 bits per pixel. An 8-bit grayscale image encodes 256 distinct gray levels; higher bit depths allow finer gradations and smoother transitions.

Converting color to grayscale usually involves computing a luminance value that approximates human perception. The most common formula for sRGB images is Y = 0.2126 R + 0.7152 G + 0.0722 B, though weighted sums with different coefficients exist. Averaging R, G, and B is a simpler alternative but can bias results toward mid-tones. Gamma correction and linearization can affect the outcome.

Grayscale is widely used in photography, film, printing, and computer vision because it reduces data complexity and can emphasize structure and contrast. It is also used in medical imaging (e.g., X-rays), document scanning, and graphics design as a neutral tonal palette.

Grayscale differs from black-and-white images, which are typically binary (two levels). Grayscale preserves a range of shades, while color information is absent. Dithering can introduce simulated color or tone when reducing color images to grayscale.