Red Eye Remover

Why flash causes red eye

Red eye is a reflection, not a colour problem. Light from the flash travels into the eye, bounces off the back of the retina, which is richly supplied with blood vessels, and returns through the pupil into the camera. The camera records that returned light as red. It happens when the flash is close to the lens axis, because only then does the light find its way straight back. Moving the flash away from the lens, as a camera with a flash away from the lens does naturally, largely prevents it.

NoteFlash close to the lens axis is the cause. Moving the flash fixes the problem at the source.

What a correct fix actually does

Fixing red eye is a desaturating and darkening operation applied to a specific region, and the whole difficulty is the region. The red is confined to the pupil and sometimes a little of the surrounding iris, because those are the parts reflecting the light back. Pushing the red out of the whites of the eye as well is what makes an automatic fix look like a smudge, because real eyes do have blood vessels in the sclera and desaturating them removes what should be there. A manual adjustment that affects the pupil and iris only, and leaves the sclera alone, keeps the eye looking like an eye.

• The red sits in the pupil and sometimes the iris.
• The sclera also has vessels and should not be fully desaturated.
• A broad automatic fix smudges the whites of the eye.
• A manual adjustment limited to the pupil and iris looks natural.
• Match the result to the other eye in the photo.

Where a manual correction is worth the effort

On a single portrait at full size, the difference between an automatic pass and a careful manual adjustment is obvious, and the manual work takes a minute. Across a set of a hundred event photographs, the economics change, and an automatic pass with a check is more realistic. The middle case is a wedding or a family photo where one or two faces matter: correct those by hand and leave the rest automatic. What is not worth doing is the same heavy manual correction applied identically to every frame, which is slower than automatic and rarely better.

• One important portrait: manual correction is worth the minute it takes.
• A hundred event photos: automatic plus a spot check is realistic.
• A few key faces in a large set: correct those by hand.
• Do not hand correct a whole set identically. It is slower and not better.

It is easier to prevent than to fix

Every factor that causes red eye can be avoided at the point of capture. Ask subjects to look slightly above or to the side of the camera rather than straight into it. Use a flash away from the lens if the camera has one. Turn the room lights on so the pupils are smaller and the flash contributes less. Any of these removes the problem entirely, while the correction is always a repair of a photograph that would have been better if it had not happened.

• Ask the subject to look slightly above or beside the camera.
• A flash positioned away from the lens largely prevents it.
• Room lights make the pupils smaller, so the flash matters less.
• Prevention is always better, and it takes nothing at edit time.