rgb2xyz

Convert RGB to CIE 1931 XYZ

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).

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

Examples

Convert RGB to XYZ

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

RGB — RGB color values

numeric array

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 Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: xyz = rgb2xyz([.2 .3 .4],WhitePoint="d50")

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: xyz = rgb2xyz([.2 .3 .4],"WhitePoint","d50")

ColorSpace — Color space of input RGB values

"srgb" (default) | "adobe-rgb-1998" | "prophoto-rgb" | "linear-rgb"

Color space of the input RGB values, specified as "srgb", "adobe-rgb-1998", "prophoto-rgb", or "linear-rgb". If you specify "linear-rgb", then rgb2xyz assumes the input RGB values are linearized sRGB values.

Data Types: string | char

WhitePoint — Reference white point

"d65" (default) | "a" | "c" | "e" | "d50" | "d55" | "icc" | 1-by-3 vector

Reference white point, specified as a 1-by-3 vector or one of the CIE standard illuminants listed in the table.

Value	White 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 | string | char

Output Arguments

XYZ — Converted XYZ color values

numeric array

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");
  

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• rgb2xyz supports the generation of C code (requires MATLAB^® Coder™). For more information, see Code Generation for Image Processing.

• If Whitepoint is a character vector, it must be compile-time constant.

• ColorSpace must be a compile-time constant.

Version History

Introduced in R2014b

R2024b: Generate C code using MATLAB Coder

rgb2xyz now supports the generation of C code (requires MATLAB Coder).

R2022b: Support for ProPhoto (ROMM RGB) color space

rgb2xyz now supports the ProPhoto (ROMM RGB) color space, which has a wider gamut than the sRGB and Adobe RGB 1998 color spaces. To use the ProPhoto color space, specify the ColorSpace name-value argument as "prophoto-rgb".