09
Understanding Color
by Tom ·
One of the most critical and difficult tasks in digital photography is also one of the most misunderstood. Managing color is even harder if it isn’t clear what we mean when we are talking about color. I know it is hard, because I have taken college courses in photography where the instructor gave wrong information because she didn’t understand. Well, here goes my shot at explaining what is going on.
First, you have to realize that different people mean entirely different things when they talk about color. Take me, for example. I’m a physicist, so let’s start with that perspective. When I think of color, I think of the part of the electromagnetic spectrum that we can see. The color of the light corresponds to the wavelength, or energy, of the photons flying around in space. There are lots of photons with too much energy to see (ultraviolet light, x-rays, gamma rays for example) and lots of photons with too little energy to see (examples are infrared light, radio waves, brain waves, and electomagnetic waves generated by powerlines). But, as you know since you are able to see your computer monitor and read this, there is a whole bucketfull of photons with just the right energy to stimulate the nerves in our retinas and allow us to see stuff. And to a physicist (or a 4th grader studying rainbows) each of those photons has a color associated with it that depends on it’s energy. For example, we see 510nm photons as green light and 475nm photons as blue light. A photon that isn’t exactly 510nm, say 509nm, will still be green, but a different shade. So, to a physicist, there are many, many colors. All of these colors come streaming to us from the sun and together make up what we call white light.
So how does your printer or computer monitor work? If you’ve thought about it at all, you probably realize that your monitor does not reproduce all the wavelengths of light that were in the original scene you thought was pretty enough to photograph. It turns out that our eyes are sensitive to only three different colors. By taking the three-color input from your eye, you brain can do a pretty good job of imagining what all the colors in a scene are. So your printer or monitor takes advantage of the three-color phenomenon.
They do it differently, though. Monitors radiate light while prints absorb light. Your monitor reproduces different relative intensities of the three primary colors; red, green, and blue. Your eye and mind detect these three colors and reconstruct the original scene. The more levels of red, green, and blue your monitor can reproduce, the more variations in color it can fool you into perceiving.
Printers do a similar trick, but rely on tints to absorb the light that falls on the print. The three primary tints are magenta, cyan, and yellow. Most printers throw in black because it is hard to get the three tints in exactly the right ratio under various lighting conditions to give a good black. Furthermore, you can’t fool your eye into seeing all the colors your brain is capible of interpreting with just three tints and black. So high-end printers add more tints to reproduce a few more of colors at the edge of their printable color gamut and more closely match all the colors your eye can differentiate.
Now comes the hard part. Making the image on the monitor look the same as the original scene, and then making the print look like the monitor. Before you give yourself a headache by banging your head against the wall in frustration, realize that the matching job is more than hard, it’s impossible. You can get close, though.
Calibrate your monitor so the relationship between the image, the monitor, and the printer stays the same. Then use print profiles that you download or make yourself to get predictable printer results. With a little effort and attention to the details, you can make prints that will dazzle your friends and clients. Who knows, you might even impress the toughest judge of all: yourself.
