The Visible Spectrum: RGB Color Voodoo

Session three continues the magical mystery tour through the land of color. Now that we know that the camera actually sees color in black and white (see the two prior posts) and that RGB colors produce CMY(K) colors, we move into the voodoo behind combined colors of transmitted light.

If you were to enter a dimly lit room and shine a red light on a blank wall, it would naturally produce a red spot. Makes sense. If you shine a green light that partially overlapped the red light, part of the wall will be green, but where the green light overlapped the red light, yellow would appear. You might think that makes no sense! But wait, there’s more. If you were to shine a blue light on the wall, where the blue light overlapped the red light, a magenta color (a strange mix between hot pink and purple) would appear. And in the area where the blue, green colors overlapped, the color cyan would show up. How strange is that?

RGB_illumination

Now here’s the amazing part. The area where all these three colors overlap turns white. Who would have thought that red+green+blue=white? Welcome to the wacky voodoo world of color science. RGB Light CirclesTransmitted color light is called additive primary light, and involves frequencies, intensities, wave lengths and other geeky stuff; the magic heart and soul of the science behind the photography you are shooting.

This amazing light show happens behind the scenes every time you shoot a photo with your camera. You don’t have to understand it all, but you can’t deny that photography is both an art and a science.

Volleyball CMYK

The colors of reflected light. Overlaying these colors on a printer/printing press delivers CMYK color.

We learned last time that when the three primary RGB channels of color are sent to the printer, each color is transposed into its complimentary color (the color that opposes it) on the color wheel, producing the secondary CMY colors. The red channel produces cyan ink, the green channel produces magenta ink, and  the blue channel produces yellow ink.

Now it’s time to look at those RGB channels again, but this time as colors of light.

Volleyball RGB Light

The colors of transmitted light. Projecting light through these three color channels produces RGB color.

When these primary additive channels of transmitted light overlap (on any projected light system… projectors, televisions, and monitors), they project the combined RGB colors. Remember, in the RGB color model, blue light on green light produces cyan (rear wall) while red, green, and a bit of blue light produce tanned skin, and when equal amounts of all three colors of light are combined, they produce neutral white (Olympic rings and sand)

In its simplest form, this is the heart of color separation. The separating of RGB composite images into their individual components. The positive (RGB) version serves the photographic and video side of the industry while the negative (CMYK) version serves the print and lithographic side.

While this may seem like voodoo, it’s simply color science at work. Just thought you’d like to know. Let me know if this makes sense to you.

If you’d like to understand even more of what makes color work, how light behaves, and how easy it is to shape the light in your photographic images, here’s a suggestion. I’ve created a very entertaining and easy-to-understand video series that will teach you the fundamentals of light and color and help you to capture and produce amazing color. Go to http://gottaknowvideos.com and get Bright About Light!

 

About Herb Paynter

Herb is a published author, photographer, retoucher, color reproduction specialist and a regular writer for Digital Photography School. Download his iBook Digital Color Photography from the iTunes store and view his Light and Color video series at Gotta Know Videos.com.
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2 Responses to The Visible Spectrum: RGB Color Voodoo

  1. Rick Redfern says:

    Your paper regarding the voodoo of color had me remember the time at a conference that no longer exists, with a monitor company that no longer exists, where they were about to publicly announce a CMYK monitor. Everything seemed to be going well for the announcement until a friend of mine decided to ask a question that seemed to astound the engineers in the room.His question was: “How are you defying the laws of physics the laws of physics when the CMYK color space is made up of reflective colors when a monitor is made up of transmissive colors?” It seems everyone in the room had forgotten that fact and the announcement was suddenly cancelled.

    • Herb Paynter says:

      I didn’t attend that conference but I can certainly understand why the monitor company no longer exists. Were they the ones who invented technicolor unicorns?

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