YIQ
Other TV systems used different color spaces, such as YUV for PAL or YDbDr for SECAM.
These color spaces are all broadly related, and work based on the principle of adding a color component named chrominance, to a black and white image named luma.
I and Q can be thought of as a second pair of axes on the same graph as the YUV color space, rotated 33°; therefore IQ and UV represent different coordinate systems on the same plane.
The YIQ system is intended to take advantage of human color-response characteristics.
In YUV systems, since U and V both contain information in the orange-blue range, both components must be given the same amount of bandwidth as I to achieve similar color fidelity.
Very few television sets perform true I and Q decoding, due to the high costs of such an implementation.
The Rockwell Modular Digital Radio (MDR) was one I and Q decoding set, which in 1997 could operate in frame-at-a-time mode with a PC or in realtime with the Fast IQ Processor (FIQP).
Some RCA "Colortrak" home TV receivers made circa 1985 not only used I/Q decoding, but also advertised its benefits along with its comb filtering benefits as full "100 percent processing" to deliver more of the original color picture content.
Around 1990, at least one manufacturer (Ikegami) of professional studio picture monitors advertised I/Q decoding.
The YIQ representation is sometimes employed in color image processing transformations.
These formulas allow conversion between YIQ and RGB color spaces, where R, G, and B are gamma-corrected values.
The following formulas assume: The ranges for I and Q[1][2] are a result of the coefficients in the 2nd and 3rd rows of the RGB-to-YIQ equation matrix below, respectively.
These formulas approximate the conversion between the original 1953 color NTSC specification and YIQ.
[3][4][5] Note that the top row is identical to that of the YUV color space In 1987, the Society of Motion Picture and Television Engineers (SMPTE) Committee on Television Technology, Working Group on Studio Monitor Colorimetry, adopted the SMPTE C.[7][8][9] The previous conversion formulas were deprecated, and the NTSC standard contained in the FCC rules for over-the-air analog color TV broadcasting adopted a different matrix:[10][11] in matrix notation, that equation system is written as: Where: To convert from FCC YIQ to RGB: in matrix notation, that equation system is written as: Where:
For broadcasting in the United States, NTSC (and with it, YIQ) remained in use only for low-power television stations as of July 2011[update], well after full-power analog transmissions was ended by the Federal Communications Commission (FCC) on June 12, 2009, however these were also required to be shut down by the FCC on July 13, 2021,[13] thereby ending the use of NTSC (and YIQ for that matter) completely in that region.
