YIQ Color Model
- As we know RGB monitors requires separates signals for a red, green, and blue component of an image but television monitors use single composite signals.
- For this composite signal, NTSC use YIQ color model.
- Here parameter Y represented as luminance (brightness) while chromaticity information (hue and purity) is specified into I and Q parameter.
- Combination of all red, green, and blue intensities chosen for Y so black and white television monitors only use signal Y for brightness.
- So largest bandwidth (about 4 MHz) is assigned to Y information signal.
- The parameter I contain orange-cyan hue information that provides the flesh-tone shading and occupies a bandwidth approximately 1.5 MHz.
- Parameter Q carries green-magenta hue information in a bandwidth of about 0.6 MHz.
- An RGB signal can convert to a television signal using an encoder which converts RGB to YIQ values.
This conversion by transformation is given by:
- Similarly, the reverse of this performed by a decoder and by transformation using the inverse of above matrix as.
CMY Color Model
- A color model CMY used for hardcopy devices as we produce the picture by coating a paper with color pigments, we see the color by reflected light a subtractive process.
- When white light reflected from cyan colored ink the reflected light must have no red component that red light absorbed or subtracted from the ink.
- Similarly, magenta subtracting green component.
- Unit cube for CMY model shown in the figure below.
- Point (1,1,1) represents black because all components subtracted and origin represents white light.
- Gray can produce among main diagonal by using all three color in equal amount.
- Printing process often uses CMY model generates a color point with a collection of four ink dots, one for each primary color C, M, and Y and one dot is black.