Continuous tone

Fine Wind, Clear Morning, the second print in Hokusai's Thirty-six Views of Mount Fuji (20th century reprint). Wood block prints like this are an example of a continuous-tone image.

A continuous-tone image is one in which each color at any point in the image can transition smoothly between shades, rather than being represented by discrete elements such as halftones or pixels.

Many printing methods use discrete halftone dots of cyan, magenta, yellow, and black (CMYK). Although halftone images are not continuously toned, they can appear continuous with high enough resolution or when viewed from a far enough distance.

Examples of continuous-tone images are natural phenomena, images produced with dye-based processes, images produced with certain analog printmaking processes (intaglio, block printing, stone lithography), and paintings. Halftone prints (as produced with inkjet and offset printers), traditional film, and digital screens are not truly continuous-tone since they rely on discrete elements (halftones, grains, or pixels) to create an image. However, we can refer to things as "continuous-tone" when the illusion is so smooth that the breaks or gaps between tonal values are imperceptible to the human eye.

An example of a nearly continuous-tone device is a CRT computer screen. Here, any pixel can represent any color, because the color components of the pixel are analog and can vary in infinite steps, and hence do not need halftones to make the colors. Since the computer is a digital device, it cannot provide the CRT with infinite tone variations. In 24-bit color mode, it provides the monitor with 256 discrete steps for each channel (red, green, and blue), for a total of 16,777,216 (256³) discrete colors. A purely analog video signal can provide infinite tone variations inside its own gamut.

See also

• Halftone
• Chromogenic print
• LightJet