YIQ Color Space

The YIQ color space
YIQ is derived from the YUV color space
and is optionally used by the NTSC composite
color video standard. (The “I” stands for “inphase”
and the “Q” for “quadrature,” which is
the modulation method used to transmit the
color information.) The basic equations to convert
between R´G´B´ and YIQ are:

For digital R´G´B´ values with a range of 0– 255, Y has a range of 0–255, I has a range of 0 to ±152, and Q has a range of 0 to ±134. I and Q are obtained by rotating the U and V axes 33°. These equations are usually scaled to simplify the implementation in an actual NTSC digital encoder or decoder. Note that for digital data, 8-bit YIQ and R´G´B´ data should be saturated at the 0 and 255 levels to avoid underflow and overflow wrap-around problems.