Treebeard's Stumper 20 October 2000

Red-Eye Blues

I'm still sorting out the 380+ photos I took on our Washington D.C. trip. I'll get them on the Web soon. In the meantime, it's fun looking at the kids' trip pictures at school. One familiar problem in our photos taken at night with a flash is that some people have spooky-looking red eyes. What causes red-eye in our photographs, and how can we avoid it? Why do our eyes look red and not some other color, and why do we only notice this in flash photos? Is red-eye the same as the "eye shine" that helps many nocturnal animals see at night?

	A classic red-eye flash photo. The bright highlights are a reflection of the camera flash, but where does the red come from? (I had to guarantee anonymity to use this picture!)
	Two Dunn Middle School students with Dorothy's ruby slippers from the Wizard of Oz at the Smithsonian Museum of American History on our recent Washington D.C. school trip. The girls' eyes match the shoes (if you look close), but the flash reflection on the glass is white. (D'oh, don't point the flash straight at the glass!)
	This un-retouched flash photo of Lauren's cat is the ultimate red-eye stumper. Ok, Graybear, explain this!

I took this photo on a hard hike with my dog Mojo down the shady north-facing Los Laureles Canyon below my house. I turned off my flash hoping that a long exposure would pick up the background, but all I got was the eye shine from Mojo's eyes.	I fiddled with the contrast and gamma settings in my graphics program, and now you can see that Mojo is swimming in a rock-lined pool along the creek. The eye shine is a reflection of the ambient light in the shady canyon. Is red-eye in photos the same phenomenon?

Answer

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