Digital color modes


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COLOR MODE FOR WEB = RGB

The two main color modes used digitally are RGB (red Green Blue) and CMYK (Cyan Magenta Yellow Key=Black). RGB is the standard color mode for electronic screens (computer monitors, mobile devices, tv’s, etc.), in opposite to CMYK which is the standard color mode for 4-color offset printing.

cmyk_rgb1

The main difference is explained as follows:

RGB is an additive color mode. Starting at black (0/0/0 RGB value), the three colors are added stepwise to the maximum, which results in white color (RGB value 255/255/255 in 8bit mode). All values inbetween represent a color or a greyscale value.

On the other hand, CMYK is a subtractive color mode. We start with a blank, white paper, and print rasterized colors on it. When we print yellow color on it, for instance, we force the white paper not to reflect the complementary color of yellow, blue, NOT to be reflected. So, with adding colors on the white paper, we’re going from light to dark.

The RGB color space is wider then the CMYK color space, this explains why an image looks more vivid and contrastful on a monitor than printed. Use RGB for every kind of picture editing, and create a CMYK version for print at the end.

RGB:

This left close up foto of a LCD Monitor shows clearly how each monitor pixel is displayed by three colors – Red, Green, Blue:

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The right sample shows a close up photo of a traditional CRT (tube) monitor. Three dots make one pixel, too.

Count of colors:
Having 8 bits per pixel and color, we get 28 = 256 colours per each color value (R,G,B), and 2563  = 16’777’216 colours; known as “Truecolor” or “Millions of colours” for all possible colors in this color mode.

This means, each single pixel can have one of 16’777’216 colors (including, white, black, and greytones). 16 bit color modes allow much more color depth, but are mostly overkill for simple digital presentation needs.

CMYK:

The CMYK color mode is the basic color printing method for offset 4-color printing. The rasterized colors are applied separately on (mostly white) paper. It’s overlays allow the mix of (almost all) colors. Orange and light green colors are the most problematic colors with this method, looking much dimmer than on the (RGB) monitor. Avoid converting pictures in CMYK color mode unless you want to print it. And even then – today, almost all printing companies do the CMYK conversion from RGB files with their own, advanced RIP technologies, so in most cases you can deliver your printable files in RGB.

 

Sample of a rasterized CMYK picture and enlargement

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Sample of a CMYK printing machine with 4 colour modules:

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