rgb2xyz

Convert RGB to CIE 1931 XYZ

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Syntax

XYZ = rgb2xyz(RGB)
XYZ = rgb2xyz(RGB,Name,Value)

Description

XYZ = rgb2xyz(RGB) converts the red, green, and blue values of an sRGB image to CIE 1931 XYZ values (2° observer).

example

XYZ = rgb2xyz(RGB,Name,Value) specifies additional conversion options, such as the color space of the RGB image, using one or more name-value pair arguments.

Examples

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Open Live Script

Convert images and color values from RGB to CIE 1931 XYZ color space.

Convert RGB Image to XYZ

Read an RGB image into the workspace.

RGB = imread('peppers.png');

Convert the image to XYZ color space.

XYZ = rgb2xyz(RGB);

Display the original image alongside the new image.

figure
imshowpair(RGB,XYZ,'montage');
title('Image in RGB Color Space (Left) and XYZ Color Space (Right)');

Convert RGB Color Value to XYZ

Convert the value of white from RGB to XYZ color space. In RGB, white is represented by the vector [1 1 1].

rgb2xyz([1 1 1])
ans = 1×3

    0.9505    1.0000    1.0888

Convert RGB Color to XYZ using D50 as Reference White

XYZ_D50 = rgb2xyz(RGB,'WhitePoint','d50');

Display the first output XYZ image alongside the XYZ image with D50 as reference white.

figure
imshowpair(XYZ,XYZ_D50,'montage');
title('XYZ Image, Without (Left) and With (Right) Reference White');

Convert Adobe RGB (1998) Color to XYZ

XYZ_Adobe = rgb2xyz(RGB,'ColorSpace','adobe-rgb-1998');

Display the XYZ images generated from the default RGB and the Adobe RGB (1998) color spaces.

figure
imshowpair(XYZ,XYZ_Adobe,'montage');
title(['XYZ Image, Starting From Default RGB (Left) and Adobe RGB ',...
  '(Right) Color Space']);

Input Arguments

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RGB color values to convert, specified as a numeric array in one of these formats.

  • c-by-3 colormap. Each row specifies one RGB color value.

  • m-by-n-by-3 image

  • m-by-n-by-3-by-p stack of images

Data Types: single | double | uint8 | uint16

Name-Value Pair Arguments

Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside quotes. You can specify several name and value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

Example: rgb2xyz([.2 .3 .4],'WhitePoint','d50')

Color space of the input RGB values, specified as the comma-separated pair consisting of 'ColorSpace' and one of 'srgb', 'adobe-rgb-1998', or 'linear-rgb'. If you specify 'linear-rgb', then rgb2xyz assumes the input RGB values are linearized sRGB values.

Data Types: char

Reference white point, specified as the comma-separated pair consisting of 'WhitePoint' and a 1-by-3 vector or one of the CIE standard illuminants listed in the table.

ValueWhite Point
'a'

CIE standard illuminant A, [1.0985, 1.0000, 0.3558]. Simulates typical, domestic, tungsten-filament lighting with correlated color temperature of 2856 K. 

'c'CIE standard illuminant C, [0.9807, 1.0000, 1.1822]. Simulates average or north sky daylight with correlated color temperature of 6774 K. Deprecated by CIE.
'e'Equal-energy radiator, [1.000, 1.000, 1.000]. Useful as a theoretical reference.
'd50'CIE standard illuminant D50, [0.9642, 1.0000, 0.8251]. Simulates warm daylight at sunrise or sunset with correlated color temperature of 5003 K. Also known as horizon light.

'd55'

CIE standard illuminant D55, [0.9568, 1.0000, 0.9214]. Simulates mid-morning or mid-afternoon daylight with correlated color temperature of 5500 K.  

'd65'CIE standard illuminant D65, [0.9504, 1.0000, 1.0888]. Simulates noon daylight with correlated color temperature of 6504 K. 
'icc'Profile Connection Space (PCS) illuminant used in ICC profiles. Approximation of [0.9642, 1.000, 0.8249] using fixed-point, signed, 32-bit numbers with 16 fractional bits. Actual value: [31595,32768, 27030]/32768.

Data Types: single | double | char

Output Arguments

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Converted XYZ color values, returned as a numeric array of the same size as the input. The output type is class double unless the input type is single, in which case the output type is also single.

Tips

  • If you specify the input RGB color space as 'linear-rgb', then rgb2xyz assumes the input values are linearized sRGB values. If instead you want the input color space to be linearized Adobe RGB (1998), then you can use the lin2rgb function.

    For example, to convert linearized Adobe RGB (1998) image RGBlinadobe to CIE 1931 XYZ color space, perform the conversion in two steps:

    RGBadobe = lin2rgb(RGBlinadobe,'ColorSpace','adobe-rgb-1998');
XYZ = rgb2xyz(RGBadobe,'ColorSpace','adobe-rgb-1998');

See Also

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Topics

Introduced in R2014b

Image Processing Toolbox Documentation

Support