Color and Color Spaces

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Most people never give a second thought to color theory.  But color is one complicated subject and is a constant focus of R&D in the multi-billion dollar global printing industry.  The physics of light and optics alone scares me but overlay on top of that the fact that everyone’s eyes are different and so each of us see color differently.  How then do you achieve an accurate color reproduction of an image?  The question is how accurate is accurate enough?  Perfection is unlikely.  Beautiful is all that can be promised.  But that is really all that is needed from any printing process – organic or inorganic.  Shown below is an elementary explanation but many textbooks have been written on it so feel free to delve deeper.

The first thing to remember is that digital capture and display devices, such as CRT, LCD monitors, digital cameras and scanners, use the Red-Green-Blue (RGB) color space. Image reproduction devices such as printers, use the Cyan–Magenta-Yellow-Black (CMYK) color space.  More on that later.  When a user generates graphics on a computer for printing, or wishes to print images from a digital camera, it is a common mistake to assume that the colors on the screen will look the same in print.  It is a mistake because the different color modes render color differently. Sometimes the conversion from RGB to CMYK works without any visible problems (accurate enough). In other cases, there will be noticeable color differences between the two.  But why?

RGB is an additive color mode.  It combines the colors, red, green and blue, in various degrees to create a variety of different colors. When all three of the colors are combined and displayed to their full extent, the result is a pure white – like sunlight. When all three colors are combined to the lowest degree, or value, the result is black – absence of color. Photo editing programs typically use the RGB color mode as the default because it offers the widest range of colors.

Printers print color onto (white) paper using the CMYK color mode. This four color mode utilizes the colors cyan, magenta, yellow and black in various amounts to create the printed images. Even though the printer is adding color by laying down toner, CMYK is called a subtractive color mode because each additional color means more light is removed, or subtracted, from the light that would be reflected off of the white paper. When the first three colors are added together, the result is not pure black, but rather dark brown. K, or black, is used to completely remove light reflected from the paper in order to achieve black.  It can be helpful to think of RGB as a transmitted or projected color space and CMYK as a reflective color space.

Conventional printing with inks and toners derived from organic chemistry has been under a constant state of development for hundreds of years with the colors easily manipulated chemically in a laboratory.  Further, ink-jet technology enables the addition of colors to the standard four color CMYK.  Some ink-jet printers can lay down as many as 12 colors to achieve almost as many colors as an RGB computer screen.  Since LASER printers are limited to 4 (sometimes 5) colors, they cannot mimic the total RGB color space.  Ceramic (inorganic) printing uses LASER printers and so is limited to a 4 color reproduction.

So why print with inorganic chemistry when organic inks can give a better color match to the original art?  The answer is simple – durability.  An image printed with organic chemistry in an 8 to 12 color ink jet printer will look stunningly accurate immediately after production.  However, in the Earth’s environment, that image is constantly degrading due to oxidation and UV fading.  It will be far less stunning and far less accurate 5 years later and will continue to deviate from the original to a greater and greater extent as the inks degrade over time and are subject to abrasive wear.  Ceramic images on the other hand may be less accurate immediately after production but kiln fired ceramic items will remain essentially unaltered over time. They do not fade and are highly resistant to scratch and abrasive damage.  In the end, the trade off is driven by the importance of longevity and durability.  The ink-jet color deviation is small at first but over time will ultimately end up less accurate than the ceramic.

For further information about RGB and CMYK, see the following links:

University of California, San Diego: RGB vs CMYK