Color Coding / Color

Color Coding

1. Definitions - First of all we want to explain what Color and Color Coding is

   Color

   Color Coding

   The typical human eye can distinguish over 10,000 different colors. We use color everyday to identify, classify and determine the state of objects around us. In addition to natural colors, we use color codes for displaying color on the Computer. That is what Color Coding is used for.

2. Examples for Color Coding

   RGB

   Shadow Mask Color CRTs consist of Red/Green/Blue triples, which are selectively excited through three cathode rays (accelerated through 3 separate anode voltages) Each combination of the voltages applied creates its own characteristical color, so it is natural to characterize different colors through the intensity ratios. The Shadow-Mask-Color-CRTs can not show all the colors, that a human eye can perceive. On the other a significant portion of possible colors can be comfortably described by the three RGB values. This simple color coding has accepted elatively fast and ound its way into all operating systems, image formats and programming languages. The acceptance level is also one of the reasons for use of this technology in all flat panel displays. The final result is that the RGB model is the most important and universal color coding convention. The RGB model may be satisfactory for display purposes, but unfortunately has limitations, which make it less than useful for applications, where the color is not supposed to depend from the display used to create or display it.

   CMY und CMYK

   An active image display must fill its dark surface with light, i.e. combine the red, green and blue components into the final colors. When all three primary colors are added in equal proportions, a white color results.

A printer creates the colors the opposite way: it must create colors by eliminating - i..e. subtracting - the red, green and blue colors from the white paper background. By subtracting equal proportions of the primary colors a black color can be created. To achieve this one needs Cyan, Magenta and Yellow, colors which are complementary to RGB. The resulting CMY model is a straightforward complement of the RGB-Modell. The conversion from RGB into CMY is given by the following equations: C = 255 - R; M = 255 - G; Y = 255 - B;

1. YIQ and YUV

   In TV broadcasting the color is for all practical purposes an addition to the black and white information, provided by the so-called Y-signal: Y = g1*R+ g2*G + g3*B where g1+g2+g3 = 1.0. Two additional low-bandwidth signal pathways transport the color information in a form of weighted difference between the real signal and the Y component.

YIQ: is used in color TV norm NTSC (America and Japan).

Y-chanel = Y signal I-chanel = weighted difference between "redness" and "blueness" Q-chanel = weighted sum of "redness" and "blueness"

Y = g1*R + g2*G + g3*B Y-Bandwidth 4.2 MHz I = g3*(R-Y) - g4*(B-Y) I-Bandwidth 1.2 MHz Q = g5*(B-Y) + g6*(R-Y) Q-Bandwidth 0.6 MHz

YUV: is used in the PAL colorTV norm (Europe, Africa, Asia except for Japan, Australia) and in digital video. YUV uses similar signals as YIQ (with different weights, however, and using a coordinate system, rotated 33 degrees) but with a higher bandwidth and correspondingly higher quality.

Y-chanel = Black and white signal Y-Bandwidth 5.5 MHz U-chanel contains the difference of two weighted differences U-Bandwidth 1.3 MHz V-chanel contains the sum of two weighted differences V-Bandwidth 1.3 MHz

1. HLS, HSV, HVC

   These color models reflect the human color vision better than the RGB, CMY, YUV and YIQ models, which are targeted primarily for hardware applications. HLS, HSV, HVC are better suited for human than for electronic communication.

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