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imadjust

Adjust image intensity values or colormap

Description

example

J = imadjust(I) maps the intensity values in grayscale image I to new values in J. By default, imadjust saturates the bottom 1% and the top 1% of all pixel values. The function linearly maps pixel values between the saturation limits to values between 0 and 1. This operation increases the contrast of the output image J.

This syntax is equivalent to imadjust(I,stretchlim(I)).

J = imadjust(I,[low_in high_in]) maps intensity values in I to new values in J such that values between low_in and high_in linearly map to values between 0 and 1.

example

J = imadjust(I,[low_in high_in],[low_out high_out]) maps intensity values in I to new values in J such that values between low_in and high_in linearly map to values between low_out and high_out.

J = imadjust(I,[low_in high_in],[low_out high_out],gamma) maps intensity values in I to new values in J, where gamma specifies the shape of the curve describing the relationship between the values in I and J.

example

J = imadjust(RGB,[low_in high_in],___) maps the values in truecolor image RGB to new values in J. You can apply the same mapping or unique mappings for each color channel.

newcmap = imadjust(cmap,[low_in high_in],___) maps the values in colormap cmap to new values in newcmap. You can apply the same mapping or unique mappings for each color channel.

Examples

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Read a low-contrast grayscale image into the workspace and display it.

I = imread('pout.tif');
imshow(I)

Figure contains an axes object. The axes object contains an object of type image.

Adjust the contrast of the image so that 1% of the data is saturated at low and high intensities, and display it.

J = imadjust(I);
figure
imshow(J)

Figure contains an axes object. The axes object contains an object of type image.

Read a low-contrast grayscale image into the workspace and display it.

I = imread('pout.tif');
imshow(I);

Figure contains an axes object. The axes object contains an object of type image.

Adjust the contrast of the image, specifying contrast limits.

K = imadjust(I,[0.3 0.7],[]);
figure
imshow(K)

Figure contains an axes object. The axes object contains an object of type image.

Read an RGB image into the workspace and display it.

RGB = imread('football.jpg');
imshow(RGB)

Figure contains an axes object. The axes object contains an object of type image.

Adjust the contrast of the RGB image, specifying contrast limits.

RGB2 = imadjust(RGB,[.2 .3 0; .6 .7 1],[]);
figure
imshow(RGB2)

Figure contains an axes object. The axes object contains an object of type image.

Read an image into the workspace, and display it.

I = imread('pout.tif');
imshow(I)

Figure contains an axes object. The axes object contains an object of type image.

Calculate the standard deviation and the image mean for stretching.

n = 2;  
Idouble = im2double(I); 
avg = mean2(Idouble);
sigma = std2(Idouble);

Adjust the contrast based on the standard deviation.

J = imadjust(I,[avg-n*sigma avg+n*sigma],[]);

Display the adjusted image.

imshow(J)

Figure contains an axes object. The axes object contains an object of type image.

Input Arguments

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Grayscale image, specified as an m-by-n numeric matrix.

Data Types: single | double | int16 | uint8 | uint16

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

Data Types: single | double | int16 | uint8 | uint16

Colormap, specified as a c-by-3 numeric matrix with values in the range [0, 1]. Each row is a three-element RGB triplet that specifies the red, green, and blue components of a single color of the colormap.

Data Types: double

Contrast limits for the input image, specified in one of the following forms:

Input TypeValueDescription
Grayscale image1-by-2 vector of the form [low_in high_in]Specifies the contrast limits in the input grayscale image that you want to map to values in the output image. Values must be in the range [0 1.0]. The value low_in must be less than the value high_in.
RGB image or colormap2-by-3 matrix of the form [low_RGB_triplet; high_RGB_triplet]Specifies the contrast limits in the input RGB image or colormap that you want to map to values in the output image or colormap. Each row in the array is an RGB color triplet. Values must be in the range [0 1]. The value low_RGB_triplet must be less than the value high_RGB_triplet.
RGB image or colormap1-by-2 vector of the form [low_in high_in]Specifies the contrast limits in the input RGB image that you want to map to values in the output image. Each value must be in the range [0 1.0]. The value low_in must be less than the value high_in. If you specify a 1-by-2 vector with an RGB image or colormap, then imadjust applies the same adjustment to each color plane or channel.
All types[] If you specify an empty matrix ([]), then imadjust uses the default limits [0 1].

imadjust clips value below low_in and above high_in: Values below low_in map to low_out and values above high_in map to high_out.

Data Types: single | double

Contrast limits for the output image, specified in one of the following forms:

Input TypeValueDescription
Grayscale image1-by-2 vector of the form [low_out high_out]Specifies the contrast limits of the output grayscale image. Each value must be in the range [0 1].
RGB image or colormap2-by-3 matrix of the form [low_RGB_triplet; high_RGB_triplet]Specifies the contrast limits of the output RGB image or colormap. Each row in the array is an RGB color triplet. Values must be in the range [0 1].
RGB image or colormap1-by-2 vector of the form [low_out high_out]Specifies the contrast limits in the output image. Each value must be in the range [0 1]. If you specify a 1-by-2 vector with an RGB image or colormap, then imadjust applies the same adjustment to each plane or channel.
All types[] If you specify an empty matrix ([]), then imadjust uses the default limits [0 1].

If high_out is less than low_out, then imadjust reverses the output image, as in a photographic negative.

Data Types: single | double

Shape of curve describing the relationship of input and output values, specified as a nonnegative scalar or a 1-by-3 numeric vector.

  • If gamma is less than 1, then imadjust weights the mapping toward higher (brighter) output values.

  • If gamma is greater than 1, then imadjust weights the mapping toward lower (darker) output values.

  • If gamma is a 1-by-3 vector, then imadjust applies a unique gamma to each color component or channel.

  • If you omit the argument, then gamma defaults to 1 (linear mapping).

Data Types: double

Output Arguments

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Adjusted image, returned as a grayscale or RGB image. J has the same size and class as the input grayscale image I or truecolor image RGB.

Data Types: single | double | int16 | uint8 | uint16

Adjusted colormap, returned as an c-by-3 numeric matrix of the same class as the input colormap, cmap.

Data Types: single | double

Extended Capabilities

Version History

Introduced before R2006a