Red-Eye Effect; Red Eye; Red-EyeThe ‘red-eye’ or ‘red eye’ effect is sometimes found in the eye of a photographic subject. When posing for a photograph a subject has bright red pupils in the centre of their eye when the image is created. In fact this is due to a reflection from the eye.
The problem is usually caused by a camera flash or other bright light-source. The source creates a light beam almost parallel with, and close to, the optical path of the camera lens. The light entering the eye is reflected off the back of the eye (called the retina) then directly into the lens of the camera. The red colour and blood vessels on the retina give the light its red colour. This colour is recorded by the camera.
The red-eye effect is readily created with point-and-shoot cameras and with pop-up flash on DSLRs. These often have a flash very close to the lens creating a direct beam into the eye and reflecting straight back into the lens. The angle between the two beams of light is very small. The effect can occur (less frequently) with other cameras or light set ups.
Red eye is easily removed by post processing software- You will need to check the help files for your image editor to see how to do it. Some cameras also detect it and can be set to remove it. The software technology for auto-removal of red-eye is still developing.
The red-eye effect is sometimes confused with the closely related eye-shine effect. However, the eyeshine effect is caused by reflection from a special membrane normally only found in nocturnal hunting birds and animals and also in fishes.