Color Space And Bit Depth

Digital image files are made up of computer words made out of 'bits', which are either Zero or One, thus the term DIGITAL. There are 8 bits to the byte. Each pixel has a computer 'word' that assigns the pixel's color and the pixel's mapped location within the rectangular area of the digital image. Thus the term ‘bitmapped’ image.

There are different color spaces available to the digital imaging enthusiast. For our home digital darkroom we will only need to be familiar with the RGB and CMYK color spaces.

RGB stands for the additive colors* of RED, GREEN and BLUE. In a basic sense RGB colors are blended (added together) from light waves containing combinations of these colors. RGB color only truly exists as light waves on your computer monitor or TV and other projected light systems (refracted light). Scanner and digital camera images are always created using RGB color.

The number of bits in the computer words used to assign the color for each of the digital image's pixels is either 24 bits or 48 bits. 24 bit images use one 8 bit computer 'word' per color (RED GREEN AND BLUE) to describe the color of each pixel. 48 bit images use one 16 bit 'word' to describe color for each pixel. More subtle color gradations are possible with 16 bit color because there is more data to work with.

All printers that use inks in their printing process use the subtractive colors** of CMYK which are CYAN, MAGENTA, YELLOW and K for BLACK. The dyes used in printing systems are designed to reflect certain colors only. So in any given color printed media the other colors of the rainbow are subtracted by lack of reflectivity for those colors. In a home PC digital darkroom the conversion from RGB color space of a digital image file to the CMYK color space for the printer is done automatically by the printer's driver software. All printed media is in the CMYK color space

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The following was copied from
http://www.bway.net/~jscruggs/

*Additive Color Synthesis is the method of creating color by mixing various proportions of two or three distinct stimulus colors of light. These primary colors are commonly red, green, and blue, however they may be any wavelengths to stimulate distinct receptors on the retina of the eye.

The distinguishing features of additive color synthesis are that it deals with the color effects of light rather than with pigments, dyes, or filters, and that the stimuli come from separate monochromatic sources. The most common example of additive color synthesis is the color television screen, (or RGB monitor), which is a mosaic of red, green, and blue phosphor dots; at normal viewing distances the eye does not distinguish the dots, but blends or adds their stimulus effects to obtain a composite color effect.

**SUBTRACTIVE COLOR SYNTHESIS uses paints, dyes, inks, and natural colorants to create color by absorbing some wavelengths of light and reflecting or transmitting others. This subtractive action is the basis of photographic filters, almost all films and color papers, and photomechanical reproduction in color.

White light is composed of all visible wavelengths, which can be divided into three primary-color bands, red, green and blue. A colorant that absorbs one wavelength band has the combined color of the other two; it is the complement of the color it subtracts from white light.