chromadapt

Adjust color balance of RGB image with chromatic adaptation

Syntax

B = chromadapt(A,illuminant)

B = chromadapt(A,illuminant,Name,Value)

Description

B = chromadapt(A,illuminant) adjusts the color balance of sRGB image A according to the scene illuminant. The illuminant must be in the same color space as the input image.

B = chromadapt(A,illuminant,Name,Value) adjusts the color balance of A using name-value arguments to control additional options.

Examples

Color Balance Image by Specifying Gray Pixel

Read and display an image with a strong yellow color cast.

A = imread('hallway.jpg');
imshow(A)
title('Original Image')

Pick a pixel in the image that should look white or gray, such as a point on a pillar. Do not pick a saturated pixel, such as a point on the ceiling light. Display the selected point in green.

x = 2800;
y = 1000;
gray_val = impixel(A,x,y);
drawpoint('Position',[x y],'Color','g');

Use the selected color as reference for the scene illumination, and correct the white balance of the image.

B = chromadapt(A,gray_val);

Display the corrected image. The pillars now appear white as expected, and the rest of the image has no yellow tint.

imshow(B)
title('White-Balanced Image')

Color Balance Image in Linear RGB Color Space

Open an image file containing minimally processed linear RGB intensities.

A = imread("foosballraw.tiff");

The image data is the raw sensor data after correcting the black level and scaling to 16 bits per pixel. Interpolate the intensities to reconstruct color. The color filter array pattern is RGGB.

A = demosaic(A,"rggb");

Display the image. Because the image is in linear RGB color space, apply gamma correction so the image appears correctly on the screen.

A_sRGB = lin2rgb(A);
imshow(A_sRGB)
title("Original Image")

The image has a ColorChecker® chart in the scene. To get the color of the ambient light, display the RGB values of a pixel in one of the neutral patches of the chart. The intensity of the red channel is lower than the intensity of the other two channels, which indicates that the light is bluish green.

x = 1510;
y = 1250;
light_color = [A(y,x,1) A(y,x,2) A(y,x,3)]

light_color = 1×3 uint16 row vector

    7361   14968   10258

Balance the color channels of the image. Use the ColorSpace name-value argument to specify that the image and the illuminant are expressed in linear RGB.

B = chromadapt(A,light_color,"ColorSpace","linear-rgb");

Display the color-balanced image with gamma correction.

B_sRGB = lin2rgb(B);
imshow(B_sRGB)
title("Color-Balanced Image")

Confirm that the gray patch has been color balanced. The three color channels in the color-balanced gray patch have similar intensities, as expected.

patch_color = [B(y,x,1) B(y,x,2) B(y,x,3)]

patch_color = 1×3 uint16 row vector

   13010   13010   13010

Input Arguments

A — RGB image

m-by-n-by-3 numeric array

RGB image, specified as an m-by-n-by-3 numeric array.

Data Types: single | double | uint8 | uint16

illuminant — Scene illuminant

3-element numeric vector

Scene illuminant, specified as a 3-element numeric vector. The illuminant must be in the same color space as the input image, A.

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: I2 = chromadapt(I,uint8([22 97 118]),ColorSpace="linear-rgb") adjusts the color balance of an image, I, in linear RGB color space.

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

Example: I2 = chromadapt(I,uint8([22 97 118]),"ColorSpace","linear-rgb") adjusts the color balance of an image, I, in linear RGB color space.

ColorSpace — Color space

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

Color space of the input image and illuminant, specified as "srgb", "adobe-rgb-1998", "prophoto-rgb", or "linear-rgb". Use the "linear-rgb" option to adjust the color balance of an RGB image whose intensities are linear.

Data Types: char | string

Method — Chromatic adaptation method

"bradford" (default) | "vonkries" | "simple"

Chromatic adaptation method used to scale the RGB values in A, specified as one of these values.

• "bradford"—Scale using the Bradford cone response model

• "vonkries"—Scale using the von Kries cone response model

• "simple"—Scale using the illuminant

Data Types: char | string

Output Arguments

B — Color-balanced RGB image

m-by-n-by-3 numeric array

Color-balanced RGB image, returned as an m-by-n-by-3 numeric array of the same data type as A.

References

[1] Lindbloom, Bruce. Chromatic Adaptation. http://www.brucelindbloom.com/index.html?Eqn_ChromAdapt.html.

Version History

Introduced in R2017b

R2022b: Support for ProPhoto (ROMM RGB) color space

chromadapt 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".