Colour centre in humans as an area specialized for colour vision. V2, also called the prestriate cortex, is believed to have a small role in colour processing by projecting signals from V1 to the V4-complex. Whether or not colour selective cells are present in V2 is still being investigated. Some optical imaging studies have found small clusters of red-green colour selective cells in V1 and V2, but not any blue-yellow colour selective cells. Other studies have shown that V2 is activated by colour stimuli, but not colour after images.[8] V4 also has feedback on V2, suggesting that there is a defined network
Colour cast used to reduce the blueish tint caused by daylight. Blue filters reduce the orange colour caused by incandescent light. A variety of coloured filters in varying degrees of intensity are available. Kodak's amber filters, for example, vary from palest yellow ("81C") to deepest amber ("85B"). A photographer chooses which filter to use based on the quality of the ambient light. Colour temperature meters can read the temperature of the existing lighting conditions and guide the selection of the filter. Clouded sky, for example, requires a paler amber than clear blue sky. If a filter is unavailable, flash is an alternative