The red eye effect

The 'red eye' effect gives the subject an unfortunate bright red colour in the pupils.

The 'red eye' effect gives the subject an unfortunate bright red colour in the pupils.

Red-Eye And How To Stop It

Just occasionally photographers are presented with an image showing the ‘red-eye’ effect. This strange effect introduces a new dimension into the photograph, often ruining it. It’s caused by a beam of light from a flash being directed into the eye and reflected out, directly into the camera lens. You can find out more about how it is caused in our glossary entry, Red eye Effect (definition).

The reflected light off the back of the eye (called the retina) is red because of the blood rich tissue found there. The strong red tones colour the reflected light. This lights up the pupil and makes the eye glow red.

The root cause of the red eye effect is the flash being too close to the lens. Red eye is a common problem in studios and portraiture photography. It is under these conditions that the effect is most likely to show up. Smaller point-and-shoot cameras are much more likely to cause the effect because the flash is so close to the lens. Using a DSLR may help. However, pop-up flash on DSLRs is also a cause of the problem.

The Remedy

Many recent cameras including point-and-shoot cameras and DSLRs have red eye correction facilities built in. Some cameras generate a diffused but direct light before the flash goes off. This causes the pupil to reduce in size unconsciously before the shot is taken. It is an effective remedy, but may cause people with sensitive eyes to blink or squint which can affect the shot. Some cameras ‘recognise’ an incidence of red eye and auto-correct the redness in-camera processing of the image after the shutter has closed.

Experienced photographers prefer real-world methods of red eye reduction. In-camera processing systems don’t always prevent red eye. Furthermore, small pupils look unnatural and harsh. Also, direct lighting from flash close to the lens is unflattering. See Does pop-up flash ruin your shots.

The most effective prevention of the red eye effect is to move the flash further from the lens. It is common for professional photographers to use off-camera flash, or flash brackets to move the flash away from the lens. This increases the angle between the flash beam to the eye and the reflection from the back of the eye. The wider angle stops the red eye effect since the reflection is not directly back out of the eye.

The red-eye effect is found more frequently in low light conditions as the eye opens the pupil to let in more light. It is more likely to occur in these conditions because there can be a wider angle of light and still get a viable reflection out of the wide pupil. One way to reduce red eye is therefore to increase the ambient light. The eye will react so the pupil closes to a smaller hole. This reduces the possibility of a reflection.

Often red eye is less detectable if you move further away. Close use of a hard light source or close-up use of the camera can both make the effect brighter. If you take the shot further away the camera may not even see red eye if it occurs.

Another way to reduce red eye is to bounce the flash light off a wall, ceiling or reflector so there is no direct flash beam entering the eye. This is more effective since the light is even and less directed.

The best way to prevent red eye is not to use flash or bright directed lights at all. In this case, lower light conditions may require the use of a tripod for a longer exposure. However, I accept that longer exposures or a tripod may not be practical or helpful.

The only other practical way to prevent red eye is to ask the subject to look away from the flash and lens slightly. Again, that my spoil the pose. And, as you can see from the picture above may not work anyway.

Software removal

Usually, one or a combination of the above, are sufficient to stop the problem in-camera. However, as a last resort many software editors can be used to remove the effect in post-processing. Adobe Photoshop has several ways to remove red-eye. Adobe Elements has a tool as well. Gimp External link - opens new tab/page, the open-source image editing suite has a red-eye tool which is included in the core system in more recent versions. Irfanview is a respected and free download image viewer. The application has gained some editing tools over the last few years. It has a basic red eye tool too. Other software suites provide various options as well. The actual methods of using these tools vary according to the software, but in most cases the process is simple.

If you don’t have your own software suite to do your red eye processing there are a number of online solutions. Google provided this page of ‘Red Eye Correction External link - opens new tab/page‘ links.

Animals

The red eye effect is also found in most animals aside from humans, although the red colour can vary in intensity and tone according species. The red eye effect should not be confused with the ‘eyeshine effect‘ found in some nocturnal hunting animals. Although the cause is the same, the reflecting membrane in the eye is different. The colours vary and are usually silvery, not red. Animals like dogs and cats can exhibit both the red-eye effect and eyeshine at different times and various light conditions. Eyeshine is prevented in much the same way as red eye.

By Damon Guy (author and Photokonnexion editor)

Damon Guy - Netkonnexion

Damon Guy (Netkonnexion)

Damon is a writer-photog and editor of this site. He has run some major websites, a computing department and a digital image library. He started out as a trained teacher and now runs training for digital photographers.
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