Removing Red Eye
A common problem with flash photography is that demonic look people get with what we call the Red Eye Effect. It happens when we take a picture with a flash in low light. Because the person’s pupils are opened very wide due to the low light, there’s nothing to stop the flash of light from traveling to the back of the eye and reflecting off of the retina. The retina is predominantly red and the red eye comes from that reflected light. Interestingly, the same effect happens with animals as well. However, with some animals the reflection is bluish instead of red.
Red Eye Reduction Mode
Some camera manufacturers have engineered a “red eye mode” to help minimize this effect. When the camera is in this mode there are two bursts of light. The first is a low powered pre-flash which causes the dilated pupils to contract quickly minimizing the amount of light reflected from the retina. Then the main flash fires to capture the image. However, this will only minimize the effect. This also may cause the subjects to blink or turn away after the pre-flash, unaware that their picture has not yet been taken.
Editing Out the Red Eye
If the red eye is captured on your image, you can try to correct it in post production with a photo editing program like Photoshop which has a red eye correction function. Otherwise, you can fix it manually by enlarging the red eye on your screen and painting it out with the brush tool, or by manipulating the color.
Avoiding Red Eye
The best solution is to avoid red eye to begin with. You can do this by insuring the subject is not looking straight at the camera. Or, if you do want the subject making eye contact with the viewer, use an off camera flash to minimize reflection off the retina.
Because red eye is a product of flash photography, take some time and learn more about flash photography.