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Understanding Color

Color is such a constant part of our lives, that most people do not take the time to consider how or why color effects their photography, and to have an in-depth understanding of how to work with color from the original capture to final printing and displaying.

Color is the visual characteristic of light described by a specific name. Specifically, color is light, and light is composed of many colors.

The colors that we can see form the visual wavelengths of perceptible color: red, orange, yellow, green, blue, and violet. Colors absorb certain wavelengths and reflect others back to your eyes. We perceive these viewable wavelengths as specific colors.

Additive and Subtractive Colors

Additive colors involve light transmitted directly from a source and viewed by a sensor (such as a human eye). The most common form of additive light is a television or computer screen. It should be noted that additive color is a property of the way our eyes perceive color, and not a property of light itself.

Subtractive colors involve reflected light such as in the mixing of paints or inks. Reflective colors absorb certain wavelengths of light and reflect others. An example of this would be a red apple, which when viewed under a white light appears red. However, it doesn’t emit red light, but actually absorbs some of the wavelengths that make up white light, reflecting only the wavelengths that humans see as red.

There are three groups that primary colors fall into:

RGB (Red – Green – Blue): The main color mode of transmissive and additive color electronic imaging devices.

CMY(K) (Cyan – Magenta – Yellow – Black): The reflective and subtractive colors of printing inks.

YRB (Yellow – Red – Blue) The reflective primary colors taught traditionally in art school, which are subtractive.

We will be primarily concerned with CMYK and RGB colors, as the Yellow Red Blue primaries have little barring on digital imaging, however are important in a purely aesthetic sense to a photographer.

When an image is recorded by a digital camera or converted to a digital format by an input device such as a scanner, it is recorded in the RGB color mode.

There are several varieties of RGB color, however most will be one of the following three:

Adobe RGB: The Adobe RGB color space is an RGB color space developed by Adobe Systems in 1998. It was designed to encompass most of the colors achievable on CMYK color printers, but by using RGB primary colors on a device such as the computer display. The Adobe RGB color space encompasses roughly 50% of the visible colors specified by the Lab color space, improving upon the gamut of the sRGB color space primarily in cyan-greens.

sRGB: or standard RGB, is an RGB color space created cooperatively by Hewlett-Packard and Microsoft Corporation. sRGB was designed to match what CRT monitors color display in 1996. This is a small gamut color space in comparison to Adobe or Pro Photo RGB, and encompasses only 35% of the visible colors specified by the Lab color space.

ProPhoto (or wide gamut) RGB: Is a very large gamut compared to Adobe RGB. It contains more saturated reds, greens and blues, but this size comes at a cost. Its green and blue primaries are imaginary, meaning ProPhoto wastes a small percentage of its space on colors we can’t see, much less print. The result is that you have fewer real color levels that will reproduce in print or on screen with which to work in Photoshop.

A standard digital color workflow will normally consist of capturing the original image in the widest gamut (or range) of colors possible. This will be your master archive copy. Often this will be recorded in a camera raw format, which will also give you 16-bit images.

It should be noted that recording in a camera Raw format, while it has it’s advantages, only has the downsides of being much larger files and taking considerably longer to view and manipulate in post-processing.

By keeping a master archive copy of a digital image, you will have the widest gamut possible color mode, which you can they save as a .jpg or .tif with a defined color space for its intended output.

For instance, if you have a Raw image which you will be uploading to a website, you can open the camera Raw file through ACR (Adobe Camera Raw), with a ProPhoto profile selected. You would then do a “Convert To Profile” choosing sRGB as the intended output profile, as the available colors in the sRGB color profile match the majority of color monitors today.

If you were preparing an image to be sent to press for a printed project, you would complete the same sequence, but when converting to profile, you would choose a CMYK profile such as US Sheet-fed Coated v2.

This workflow ensures that you have an image with the widest possible color profile, which you will then change based on each specific output.

Another good article, Chris. I know that this is a 'primer', but is it worth saying that breaking colours up into three primaries (RGB) is just a convenience, albeit one that comes close to the way our eyes work? It is possible to use more divisions. You could have seven if you wish - and some people do use seven for more accurate representation. Though slightly different, and not digital, Fuji uses four colour-sensitive layers in colour film.

Best,
Helen

Chris:

I don't know if this will upload well - I may have to post it in my portfolio, but I tried to make a color chart last night in Illustrator to show the differences between value, tint, brightness, and contrast - with some common terms used to describe color. I made a color wheel shading to white (tint), black (value), and grey (desaturation) as well as a contrast wheel - b + w to grey.

"It should be noted that additive color is a property of the way our eyes perceive color, and not a property of light itself."

That's as far as I got into that Helen, but I agree. I wasn't sure how much science to give this, as a lot of color theory is too deep for the average hobbyist.

Alot of it is applying understandable, digestable words to a massive spectrum of wavelengths, a small fraction of which is visible to the human eye.

The true color spectrum really has nothing to do with any 'set' of chosen primary colors, but is dependent on color temperatures that are linear as opposed to being mxied from primaries.

Nice work Mike. Really, excellent job creating the graph. It does well to show the values of hue, saturation and brightness & contrast. If all of us combine heads, we should be able to put up some informative, digestable articles.

Chris

I'm sorry Chris, but the image just did not post well - I have the image as a panoramic in my portfolio:

http://www.usefilm.com/image/1074725.html

This is not really a digital primer, yours speaks very well to the technical components of color, this would be for the basics of color theory and terminology of color.

The only other idea I had was if you really wanted to get into Pantone, TrueMatch, Toyo - but these are more for graphic design and print than photography.

Hi Mike, I think it looks OK.

I think Pantone and other color match systems might be more geared towards GD, but I think I should maybe have more on color profiles and modes, so along with sRGB, Adobe and ProPhoto, there could be EktaSpace, CMYK, cieLAB & HSB? Possibly others I'm overlooking?

Here is an example of an image from a ten-channel multispectral digital camera, where the spectral information has been used to imitate the appearance of the painting under different ilumination conditions.

http://www.imaging.org/pubs/jist/supplemental/2005/49_6_563/fig11.gif

Best,
Helen

W00t - good summary.

The human eye has elements for the 3 primary colours (Red, Green, and Blue) as well as elements that are only sensitive to light intensity (and can't perceive any colour).

The latter are mainly responsible for vision in low light conditions, which explains why human beings have trouble seeing colour differences in low light (the RGB sensors only trigger on higher input flux).

The colour and light intensity the human brain perceives is made up of the combination of the sensory inputs of these different sensor elements (light sensitive nerve endings in the eye).

So the eye is thus not so much different from a digicam sensor (apart from the far far higher resolution and speed of course, and the lower power consumption).

Most digicam sensors even mimmick the human eye in including more green sensitive elements (which are also in the majority in the human eye) than elements sensitive to the other primaries.

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