Everything You Need to Know About Camera Sensors

Color Reproduction

Each photodiode in a camera sensor detects only the brightness of the light. In order to reproduce colors, each cell in the sensor is covered with a colored filter that transmits only the light in a similar wavelength. For instance, a blue filter will transmit only the blue light. A red filter will transmit only the red light. Filters are created for each of the primary colors: red, green, and blue. They are laid out in a pattern, so that each photodiode will be able to transmit all three colors. Most camera sensors today use a filter called a Bayer mask filter. (Named for Dr. Bryce Bayer of Kodak) This filter lays the colors out in a grid pattern of alternating colors. Since the human eye is more sensitive to green light, the Bayer mask has two green filters for each red and blue. This creates a truer representation of what the human eye actually sees.With the color filters, each photodiode can signify a red, green, and blue value. The color value of these cells are combined and interpolated to represent the full spectrum of colors, allowing the image processor to reproduce a full color image.Currently only the Foveon sensor represents color differently. Instead of using filters, the Foveon sensor places the photodiodes at different depths within the silicon to detect the different colors. This means that each photodiode can detect all three colors without the use of a filter. Although this is proposed to create a truer color reproduction, the Foveon sensor is currently still relatively new and results are currently under scrutiny.