standardRGB {colorSpec}

Convert from XYZ to some standard RGB spaces

Description

To display an XYZ value, it typically must be converted to a standard RGB space. This is the function to do it.

Usage

RGBfromXYZ( XYZ, space )

Arguments

XYZ

a 3-vector, or a matrix with 3 columns with XYZs in the rows

space

the name of the RGB space - either 'sRGB' or 'Adobe RGB'. The match is case-insensitive, and spaces in the string are ignored.

Details

The input XYZ is multiplied by the appropriate 3x3 conversion matrix (for sRGB or Adobe RGB). These matrices are taken from Lindbloom and not from the corresponding Wikipedia articles; for the reason why see Note.

Value

An Mx3 matrix where M is the number of rows in XYZ, or M=1 if XYZ is a 3-vector. Each row of the returned matrix is filled with linear RGB in the appropriate RGB space. Values outside the unit cube are not clamped. To compute non-linear display RGB, see DisplayRGBfromLinearRGB().
In case of error the function returns NULL.

WARNING

This function is deprecated. New software should use spacesRGB::RGBfromXYZ() instead. The new function returns "signal RGB" instead of linear RGB.

Note

An RGB space is normally defined by the xy chromaticities of the 3 primaries and the white point. We follow Lindbloom in using the 'official' XYZ of the white point from ASTM E308. Using this XYZ of the white point makes the color space a little more consistent with other areas of color.
For example, from IEC 61966-2-1 we have D65 xyY=(0.3127,0.3290,1) -> XYZ=(0.9504559,1,1.0890578). But from ASTM E308, D65 XYZ=(0.95047,1,1.08883), which is a little different.

Source

IEC 61966-2-1:1999. Multimedia systems and equipment - Colour measurement and management. Part 2-1: Colour management - Default RGB colour space - sRGB. https://webstore.iec.ch/publication/6169

Lindbloom, Bruce. RGB/XYZ Matrices. http://brucelindbloom.com/index.html?Eqn_RGB_XYZ_Matrix.html

Wikipedia. sRGB. https://en.wikipedia.org/wiki/SRGB

Wikipedia. Adobe RGB. https://en.wikipedia.org/wiki/Adobe_RGB_color_space

See Also

D65, officialXYZ, DisplayRGBfromLinearRGB

Examples

RGBfromXYZ( officialXYZ('D65'), 'sRGB' )
#      R G B
# [1,] 1 1 1    # not really 1s, but difference < 1.e-7

RGBfromXYZ( c(.3127,0.3290,0.3583)/0.3290, 'sRGB' )
#              R        G       B
# [1,] 0.9998409 1.000023 1.00024    difference > 1.e-5