The Visible Spectrum: RGB Channels Explained

On my last post, I displayed this color photo of an Olympic Volleyball game. Surrounding the picture are the individual RGB channels that make up the color photo. If you really look at these individual channels, something probably doesn’t make sense. If you didn’t look closely before, look again.

The color picture shows a blue background but the Red channel’s background is the one that appears the darkest. Ask yourself how solid red makes sense in a blue background? Then ask why the Blue channel has very little tone in the background? If you haven’t figured it out yet, put your thinking cap on and keep reading.

Volleyball-RGB

Red, Green, and Blue are the “additive” primary colors that the camera captures and your eyes see on your computer monitor. These primary colors are the colors of transmitted light. They are known as additive colors because when these colors of light are combined in various proportions, they portray the colors of the visible spectrum. They are known as primary colors because they are the purist, most basic colors visible to the human eye.

When these RGB colors of light are combined, they form the additive secondary colors of Cyan, Magenta, and Yellow. These secondary colors are also known as the subtractive primary colors; the colors of inks used in the printing process. The eye sees these inks as reflected light when printed on paper. When various amounts of subtractive primary colors are combined on paper, they produce (roughly) those same colors of the visible spectrum.

ColorWheel

When these primary and secondary colors are viewed on the color wheel, the additive primary colors are located directly opposite the additive secondary colors; Cyan-Red, Magenta-Green, and Yellow-Blue.

By the way, even though you send RGB images to your inkjet printer, the printer converts those colors into CMYK (and usually a few additional) colors. Only photographic printers use RGB light to expose photographic paper.

 

This brings us to the answer to the original question. In the additive color mode, the Red channel actually represents the ink color Cyan, the Green channel represents the ink color Magenta, and the Blue channel represents the ink color Yellow. When you grasp this principle, you’ll understand why the Red channel in the picture below is actually the color Cyan, which makes more sense since the back wall of the court is pure Cyan with a little Magenta, and a touch of Yellow thrown in. In the printing process, a small amount of black is added to the image for contrast and color depth.

Volleyball-CMYK  Volleyball CMYK

If you have to think real hard to sort through all this, just be thankful that color science is alive and well in the photo-reproduction process and takes care of the color conversion from transmitted light (camera/monitor) to reflected light (printed material). This certainly doesn’t explain whole the color separation process, but it addresses the basics.

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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