Friday, October 24, 2008

Science! (Why Your Digital Camera Disagrees With You)

Ever wonder why the colors in your digital pictures don't look like the real thing? Wonder no more!

Although the makers of cameras have always tried to make it so that the film (for old, non-digital cameras) or electronic receptors (for digital ones) are only responsive to the same wavelengths of light that the human eye is, and in the same relative proportions, they're using different materials, so the match is never going to be perfect, however many filters and layers and amplifiers and etc. get added to the camera.

(Or, check that: the match will not be perfect until we're carrying around cameras made of meat. Close enough to never?)

The human eye is only capable of seeing wavelengths between about 380 (violet) and 750 (red) nanometers. I don't know what all else might be going on, but at least one of the issues with my own personal digital camera is that it's capable of seeing wavelengths of light of around 940 nm. How do I know? Because that's the frequency used by a lot of remote controls (and I'm making the somewhat unwarranted assumption that my remote must operate at 940 too). 940 nm is in the infrared range, which is not visible to the eye, but my camera can see it, as shown here:


But it gets significantly worse, because as you can tell from the photo, my camera sees this light as purple, which is on the opposite side of the spectrum from infrared. Possibly it wouldn't be that noticeable if your camera saw infrared as red: they're close enough in the spectrum that a lot of things that absorb or reflect one probably also absorb or reflect the other. But since your camera is seeing something that's close to red as being purple, which is on the opposite side of the spectrum, that adds a bit of unpredictability to the situation.

This is probably the reason for the difficulty I've mentioned in getting blue and purple plants to look right in the camera, by the way. (Probably also the issue with Saintpaulia flowers being unphotographable.) Plants that reflect a lot of infrared (or ultraviolet, too, actually) are going to end up looking more purple to the camera than plants that don't, but my eye can't tell the difference between the plants that reflect those wavelengths and the ones that don't, so sometimes colors go all weird on me, and sometimes they don't.

And that's just for the infrared. My camera probably sees ultraviolet, too; I just don't have a good way to check that one. Maybe someday.

Is there a way to fix this? Not a very practical one, unfortunately. Using a photo editing program to subtract the blue added by the camera might help, but of course that's going to subtract blue from the background and leaves and everything else, too, unless you can isolate only the flower or whatever that looks wrong. Some software will let you do that, and some won't. Somebody somewhere also probably sells filters you can use to block out infrared light, but probably it's easier just to adjust the color after the fact.

Anyway. So now you know. Take pictures of your own remote controls. See what you find. It'll be fun.


3 comments:

garden girl said...

fascinating! Thanks for explaining this!

perennialgardener said...

Very informative post & answers the questions I've had about getting good pictures of some of deeper blue blooms.

lancetx said...

Actually most (if not all) digital cameras have an infrared filter built into them. There are instructions online on how to remove that to take rather odd infrared photos. But I suspect the filter in place is only partially effective, thus you get the purple tint.

I suspect the camera image sensor can see a vastly wider range than we can. But by means of filters, both physical and in post processing in the camera brain, it removes a lot of that. Or tries to, as you've noticed, to varying degrees of success.