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Color Reproduction – An Introduction

As a precursor to discussing color contrast I think it’s worthwhile explaining, as simply as I can, some fundamental principals concerning light and color, as we perceive them, and providing a very brief introduction to color spaces.

We see light as a result of it being projected onto a pattern of light sensitive cells, referred to as rods and cones, on the eye’s retina. Rods are responsible for sharp vision and have the advantage of being sensitive to low-light contrast. This helps us see and navigate our way safely under dimly lit conditions. There are 3 types of color receptor cones that are sensitive either to red, green or blue wavelengths. Cones enable us to see color, but require brighter light to function than rods.

Light consists of many colors that reach us in waves. We perceive the light waves, which are absorbed or reflected by an object, as color.

There are numerous ways to represent color and also to illustrate relationships between colors. The RYB color model favoured by painters has Red, Yellow and Blue at equal intervals from each other around the wheel. 

Commercial print houses print onto media that uses reflected light and ink to form an image. They utilise the CMYK (Cyan, Magenta, Yellow and Key/blacK) subtractive method of printing. In theory it should be possible to produce black when aligning cyan, magenta and yellow plates of equal density together. But, in practice, a dirty brown color is produced. As a consequence the Key or black printing plate is added to the stack to provide a good black and bring out detail. It is because of this extra layer in the stack that a digital file grows in size when converting from RGB into CMYK color space.

Photographers tend to work with the RGB (Red, Green and Blue) color model favoured by still and video cameras, scanners, mobile phones, TV and computer monitor displays.

While ink jet printers utilise CMYK inks, photographers usually adjust images on the desktop within one of several RGB color spaces (sRGB, Adobe RGB or ProPhoto RGB). In a properly calibrated and profiled workflow the resulting RGB numbers, that describe the actually colors, would be translated into data appropriate for accurate reproduction by the inkjet printer. When files are to be output via a printing press the finished RGB files need to be converted into CMYK, either by the photographer or the commercial printer, prior to printing.

© Copyright All Rights Reserved

Glenn Guy, Blue Sky Photography

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