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rgbyiq

Converts RGB color values to YIQ values.

Available in version 5.0.0 and later.

Prototype

	function rgbyiq (
		rgb  : numeric   
	)

	return_val  :  numeric

Arguments

rgb

An array of Red, Green, Blue (RGB) color values. This array can be of any shape, but the rightmost dimension must be 3 for specifying the RGB values. The Red, Green, and Blue values are intensities in the range [0.,1.].

Return value

The returned value is an array of the same dimensions and dimension sizes as the input array. The input RGB values will have been replaced with their YIQ equivalents. If any values in the input array are double precision, the returned array will be double precision.

Description

This function determines the YIQ equivalents to RGB color values. The YIQ color model is used in U.S. commercial analog television and is a recoding of RGB for transmission efficiency.

The Y component (luma) is the only component used by black and white TVs. Y minimizes the effect of two colors appearing different to the human eye but mapping to similar monochrome intensities. Y values range between 0. and 1. inclusive.

The I (in-phase) component is in the range [-0.6, 0.6]. It attains its maximum when the input RGB triple is (1.,0.,0.); it attains its minimum when the input RGB triple is (0.,1.,1.) .

The Q (quadrature) component is in the range [-0.53, 0.53]. Q attains its maximum when the input RGB triple is (1.,0.,1.) and it attains its minimum when the input triple is (0.,1.,0.).

For a complete description of the algorithm see:

  1. Foley, James D. and van Dam, Andries,"Fundamentals of Interactive Computer Graphics",Addison-Wesley Publishing Company, 1982.

Missing values are not honored.

See Also

yiqrgb, hsvrgb, rgbhsv, hlsrgb, rgbhls

Examples

Example 1

The following:

begin
  yiq = rgbyiq((/1.0, 0.0, 1.0/))
  print (yiq)
end
produces:

Variable: yiq
Type: float
Total Size: 12 bytes
            3 values
Number of Dimensions: 1
Dimensions and sizes:   [3]
Coordinates: 
(0)     0.4129853
(1)     0.2743087
(2)     0.5229881
Example 2

The following:

begin
  rgb = (/ (/1.d, 0.d, 1.d/), (/0.d, 1.d, 0.d/) /)
  yiq = rgbyiq(rgb)
  print (yiq)
end
produces:

Variable: yiq
Type: double
Total Size: 48 bytes
            6 values
Number of Dimensions: 2
Dimensions and sizes:   [2] x [3]
Coordinates: 
(0,0)   0.4129853
(0,1)   0.2743087
(0,2)   0.5229881
(1,0)   0.5870147
(1,1)  -0.2743087
(1,2)  -0.5229881