COLOR_CONVERT

The COLOR_CONVERT procedure converts colors to and from the RGB (Red Green Blue) and a number of other color spaces.

RGB values are bytes in the range 0 to 255. YCbCr values are bytes with the range indicated below. Other values are in floating point.

These color spaces and their ranges are:


HLS	Hue Lightness Saturation (double cone). Also known as HSL and HSI. Hue is measured in degrees between 0 and 360, with 0 corresponding to red, 120 to green, and 240 to blue. Lightness and Saturation are floating-point values between 0 and 1.
HSV	Hue Saturation Value (single cone). Hue is measured in degrees between 0 and 360, with 0 corresponding to red, 120 to green, and 240 to blue. Saturation and Value are floating-point values between 0 and 1.
YUV	Luminance and two Chrominance. Y is a floating-point value between 0 and 1, U is a floating-point value between -0.436 and 0.436, V is a floating-point value between -0.615 and 0.615.
YIQ	Luminance In-phase Quadrature. Y is a floating-point value between 0 and 1, I is a floating-point value between -0.596 and 0.596, Q is a floating-point value between -0.523 and 0.523.
YPbPr	Luma ChromaBlue ChromaRed (analog). Y is a floating-point value between 0 and 1, Pb and Pr are floating-point values between -0.5 to 0.5.
YCbCr	Luma ChromaBlue ChromaRed (digital). Y is a floating-point value between 16 and 235, Cb and Cr are floating-point values between 16 and 240.

The input parameters may be of one of the following forms:

Three input parameters containing the input color triple(s) which may be scalars or arrays of same size. These are followed by three output parameters for returning the result.

One image array of the form (3 x m x n, m x 3 x n, or m x n x 3), followed by a single output parameter for the result.

A reference containing a discussion of the various color systems is: Foley and Van Dam, Fundamentals of Interactive Computer Graphics, Addison-Wesley Publishing Co., 1982.

Syntax

Arguments

I₀, I₁, I₂

The input color triple(s). These arguments may be either scalars or arrays of same length.

O₀, O₁, O₂

The variables to receive the result. Their structure is copied from the input parameters.

I₀

An input image array of the form 3 x m x n, m x 3 x n, or m x n x 3.

O₀

A variable to receive the result. Its structure is copied from the input parameter, I₀.

Keywords

HLS_RGB

Set this keyword to convert from HLS to RGB.

HSV_RGB

Set this keyword to convert from HSV to RGB.

INTERLEAVE

This keyword is useful only when calling this procedure with two arguments. It is ignored when using six arguments. Set the keyword to the value that corresponds to the image array's interleave format. The second output argument uses the same interleave format when returning the result. The valid values for 2D arrays (3 x n or n x 3) are:


value	array type
0	Pixel Interleave (3 x n) (default)
1	Row Interleave (n x 3)

The valid values for 3D arrays (3xmxn, mx3xn, or mxnx3) are:


value	array type
0	Pixel Interleave (3 x m x n) (default)
1	Row Interleave (m x 3 x n)
2	Planar Interleave (m x n x 3)

RGB_HLS

Set this keyword to convert from RGB to HLS.

RGB_HSV

Set this keyword to convert from RGB to HSV.

RGB_YCBCR

Set this keyword to convert from RGB to YCbCr.

RGB_YIQ

Set this keyword to convert from RGB to YIQ.

RGB_YPBPR

Set this keyword to convert from RGB to YPbPr.

RGB_YUV

Set this keyword to convert from RGB to YUV.

YCBCR_RGB

Set this keyword to convert from YCbCr to RGB.

YIQ_RGB

Set this keyword to convert from YIQ to RGB.

YPBPR_RGB

Set this keyword to convert from YPbPr to RGB.

YUV_RGB

Set this keyword to convert from YUV to RGB.

Examples

The command:

COLOR_CONVERT, 255, 255, 0, h, s, v, /RGB_HSV

converts the RGB color triple (255, 255, 0), which is the color yellow at full intensity and saturation, to the HSV system. The resulting hue in the variable h is 60.0 degrees. The saturation and value in the variables s and v, are set to 1.0.