The imager in a digital video camera consists of a single or three semiconductor chips with an array of light-sensitive cells (photocells). It transfers incident light into electric charge, while it is only able to differentiate a change in luminance and therefore only delivers a black and white image. In order to create a color image, the incident light has to be split into its color components (e.g. red, green, and blue) during capture.

Single-Chip Image

To enable the separation of color components with single chip imagers, manufacturers of digital cameras today mostly rely on the color filter array. A color filter array (CFA) is a small mosaic pattern of color filter dyes, applied directly onto the sensor. One form of a CFA is the Bayer pattern, which is used in the D-21. Each photodiode is covered with only one dye, so only the red, green, or blue component is captured. The luminance information for the two missing color components is then reconstructed or interpolated from surrounding pixels. A raster image that has not been processed is referred to as raw data (image). After color interpolation it is referred to as RGB data or image.

Enlarged image section from a raw data image with Bayer structure.

Enlarged image section of the reconstructed image.

Three-Chip Imager

In a three-chip imager, the incident light is sent through a beam splitter to divide the image into three color components. A sensor, on one of the three surfaces where the light exits the beam splitter then captures the luminance values for one color component. At each end of the beam splitter, a sensor then captures the color component images. All three sensors have to be exactly aligned, as even a small misalignment will produce color fringes in the image. 3-chip imagers are sensitive to temperature changes. A difference in the surrounding temperature between factory and shooting location already leads to slight misalignment. Another problem occurs when HD high-speed lenses are used. Light entering these lenses at a great off-angle is absorbed by some beam splitters, which causes vignetting (image gets darker in the corners).