YIQ
The YIQ color model is a color system, the luminance Y and the color differences of I ( cyan orange balance ) and Q ( magenta-green balance). Compared with the related YUV color model the color plane by 33 ° clockwise.
The YIQ color space was used exclusively in the U.S. standard for analog NTSC television. Because since the 1970 years here the YUV color model was preferred, there are no application for the YIQ color model more.
The motives for the creation of the YIQ color model in the context of the development of color television are the same as in the YUV color model. However, it was created by the rotation by 33 °, the possibility of the single color to be transmitted with different carrier bandwidth, 1.3 MHz with I and Q 400 kHz. So the human visual sensitivity is better taken into account, because the human eye is more sensitive to color impressions on the I- line cyan-orange than on the Q -Line magenta-green. In the YUV color model, the color proportions of these two lines unevenly distributed on the two color signals U and V, so that no bandwidth reduction and thus no efficient transmission is possible.
The YIQ system for B / W ( black and white) television compatible, which represents only the Y signal as a color TV map all three channels. The Y component has the largest share of the bandwidth of the television signal transmitted. This will appear Pictures of b / w TVs sharper than images of color televisions.
Conversion
The conversion of linear to the light intensity R'G'B values ( ie any existing gamma correction must first be undone ) to YIQ is in matrix notation:
To convert Y'UV according Y'IQ the components U and V are rotated by 33 ° in the counterclockwise direction, and then reversed ( U corresponds to the Q- axis). As a combined rotation and transformation matrix yields:
Due to the symmetry of this matrix, it can also be used directly for conversion back to Y'UV.