Why do people have red eyes in photos?

By Matt Horvath
Info Guru,

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Woman with red eyes
What is the cause of red eyes in photos? The explanation of this phenomenon lies in a beam of light
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Find out what causes this phenomenon and how to avoid it.

You manage to get your group of old high school friends together for a night out on the town and load up the digital camera with pictures to remember the occasion.

The next morning you move the photos onto your computer and everyone's eyes are glowing. Why do people have red eyes in photos? Strangely, the pictures from the beach do not show the same effect. What happened between day and night that caused this shift in optical hue? The explanation of this phenomenon lies in a beam of light.   

The Cause of Red Eyes

Light from the camera's flash jets across the room, penetrates the irises of your comrades at an incredible rate and causes their pupils to attempt to process the unexpected intrusion. The attempt fails and the flash mingles with the numerous blood vessels of the eye and reflects off the retina and back through the vessels to the camera lens, causing your group to look demonic.

When you walk into a low-lit room from being out on a sunny day it appears to be extremely dark because your eyes have not had a chance to adjust. This same concept is at work when the flash of a camera goes off because it doesn't give the eye any time to adjust. The effect is heightened in people with blue eyes because the iris lets more light through.

Preventing Red Eyes in Photos

The main problem is that the flash in most digital cameras is located close to the lens, the usual focal point of the subject's eyes. So, the first preventative measure would be to turn on some lights in the room so there is no need to use the flash.

However, this is not always an option when you are snapping shots in your favorite neighborhood watering hole. Another option is to have everyone divert their eyes to something other than directly at the camera.


Unfortunately, the above fixes are inconvenient when out in low-lit places and you may not want a photo of your friends looking in odd directions.  

Some cameras have built-in red-eye reduction. They let off a flicker of less abrasive light before the main flash goes off, giving the pupil time to adjust. See the camera's manual for information on availability and how to activate this feature.

Fixing Red Eyes in Photos

Of course, these techniques aren't going to help you with the boatload of photos from last night. Luckily, there is image software that can correct this occurrence. You don't need to go out and spend hundreds of dollars on the latest version of Adobe Photoshop; you may even have a free photo editor that came with your computer that will take you through a few steps to make the correction.

Unfortunately, fixing many photos can be time-consuming but it is not too difficult. Windows Vista has an automatic red-eye reduction feature in its photo viewer, but it may not always be accurate.

If you go to print photos at a drug store they may be able to help with red-eye reduction, ask the photo attendant for guidance.

Animals have an additional reflective layer in their eyes that improves night vision, making it almost impossible to avoid color alteration. Their eyes will show up in photos in a number of colors other than red and often glow white.

Human eyes that appear white in a photo can indicate cancer of the eye, so if this occurs that person should seek a professional evaluation.

Why do people have red eyes in photos? Overall, this phenomenon is hard to avoid because of the compactness of digital cameras but the avoidance techniques and post-photo fixes described above are able to help correct your final image. There is no need to call up all of your old buddies for some retakes.

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