RGB (red, green, blue)

CMYK (cyan, magenta, yellow and black)

Color Models:

RGB model: Based on the three primary colors: red, green and blue it is also referred to as the additive model. This model is for applications where different color light is passed to the human eye. That is, recognition of color does not require a reflection of external light. When all the potential light is passed to the eye, it creates white. White is the result of all the colors coming together. Similarly Black is the result of the lack of light. Red, green and blue combine with each other to create cyan, magenta and yellow (the secondary colors).

Green + Blue = Cyan

Red + Blue = Magenta

Red + Green = Yellow

CMYK model: Based on the three secondary colors: Cyan, Magenta and Yellow, it is also referred to as the subtractive model. Developed based on the light-absorbing quality of ink on paper, it is measured by reflective light creating color. That is, the CMYK model is dependent on an external light source. This means that white is created without any color, since the white paper background reflects all the light when there is no image. Black, as a result, is created when all the colors are on paper, and no light gets reflected. Since you can never achieve pure white light as an illumination source or create a pure white paper for printing purposes, cyan, magenta and yellow don’t really combine to black. So, to complete the gamut the CMYK model requires Black-K (K is used for black instead of B which can be confused with blue).


Color Gamut:

The color gamut is the range of colors that can be printed or displayed by a system. The gamut of colors that can be recognized by the human eye is substantially greater than any system developed by mankind. The RGB color gamut is substantially larger than that of CMYK. The chart below describes the range of coverage of each model compared to the gamut covered by the human eye.





While both scanners and monitors are based on the RGB model, not all scanners and monitors cover the full RGB color gamut. For example the Widecom SLC936C scanner captures many shades of black and white beyond what can be displayed on the average monitor. The quality of a color scanner is measured by the the size of gamut it can cover (what is the range of colors that it can recognize and differentiate at its extreme). Low quality scanners reach saturation in black and white prematurely.

Saturation:

Also called the chroma, saturation is the level of purity of color. In a 24bit color image, each of the primary colors is divided into 256 levels (from 0 to 255). At 255 each color reaches saturation. When all three colors reach 255, it represents a saturated white. With all three colors at 0, a saturated black is created. An effective test of a low quality color scanner is the ability to make it reach saturation from common printed matter. Some wide format color scanners get saturated white even with common photocopier bond paper. Widecom’s SLC936C scanner allows realization of various shades of the image even from bright white and dark black images.

It is possible through brightness control and contrast control to force the SLC936C scanner to reach saturation at white and black, if that is needed for your application. More importantly, if your application requires recognition of slight difference in shades at the extremes of the color table, you need an uncompromising solution as the SLC936C.


Calibration:

Calibrating the SLC936C scanner is the process of setting a white light reference point to allow for high quality accurate scanning. As environmental conditions for your scanner change, it is important to re-calibrate the scanner for optimum results.

In an environment where you are working with scanning, viewing and printing color images, it is important to calibrate the scanner, the monitor and the printer to each other. While scanners and monitors operate in the RGB color model, printers operate in the CMYK model. Interpertations of RGB to CMYK vary from one product to another, as a result it is critical to calibrate these to each other. If you display the same image on a dozen monitors, even if they are from the same manufacturer and the same model, you will see a distinct difference on how each monitor displays the image. In fact, the same monitor will display the same image differently a year from now as it would today. Monitor calibration is the most important aspect of working with color images in a digital environment. While most monitors under $ 1,000 do not have a mechanism for calibration, Adobe Photoshop provides a unique method for monitor calibration. It is highly recommended that users who do not wish to invest on a high end graphic arts monitor consider using Photoshop.