imadjust

Adjust image intensity values or colormap

Syntax

J = imadjust(I)

J = imadjust(I,[low_in high_in])

J = imadjust(I,[low_in high_in],[low_out high_out])

J = imadjust(I,[low_in high_in],[low_out high_out],gamma)

J = imadjust(RGB,[low_in high_in],___)

newcmap = imadjust(cmap,[low_in high_in],___)

Description

J = imadjust(I) maps the intensity values in grayscale image I to new values in J. When you use this syntax, 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.

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.

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

Adjust Contrast of Grayscale Image

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

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

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)

Adjust Contrast of Grayscale Image Specifying Contrast Limits

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

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

Adjust the contrast of the image, specifying contrast limits.

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

Adjust Contrast of Color Image

Read an RGB image into the workspace and display it.

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

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

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

Standard Deviation Based Image Stretching

Read an image into the workspace, and display it.

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

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)

Input Arguments

I — Grayscale image

m-by-n numeric matrix

Grayscale image, specified as an m-by-n numeric matrix. If I is an integer data type, then imadjust first rescales the pixel values to the range [0, 1] by using im2double. After adjusting the contrast by mapping values between the input and output contrast limits, the function converts the output image back to the original data type of I.

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

RGB — Truecolor image

m-by-n-by-3 numeric array

Truecolor image, specified as an m-by-n-by-3 numeric array. If RGB is an integer data type, then imadjust first rescales the pixel values to the range [0, 1] by using im2double. After adjusting the contrast by mapping values between the input and output contrast limits, the function converts the output image back to the original data type of RGB.

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

cmap — Colormap

c-by-3 numeric matrix

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

[low_in high_in] — Contrast limits for input image

2-element numeric vector | 2-by-3 numeric matrix

Contrast limits for the input image, specified as one of the values in the table.

Input Type	Value	Description
Grayscale image	1-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.
Grayscale image	Unspecified	If you specify only one input argument using the syntax imadjust(I), the function sets low_in and high_in based on the input image values so that the bottom 1% and top 1% of all pixel values are saturated.
RGB image or colormap	2-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 colormap	1-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 limits [0 1].

The imadjust function 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

[low_out high_out] — Contrast limits for output image

[0 1] (default) | 2-element numeric vector | 2-by-3 numeric matrix

Contrast limits for the output image, specified as one of the values in the table.

Input Type	Value	Description
Grayscale image	1-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 colormap	2-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 colormap	1-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	Unspecified or []	If you do not specify the output contrast limits, or 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

gamma — Shape of curve describing relationship of input and output values

1 (default) | nonnegative scalar | 1-by-3 numeric vector

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).

This graphic illustrates the shape of the transformation curves when gamma is less than 1, equal to 1, and greater than 1. In each graph, the x-axis represents the intensity values in the input image, and the y-axis represents the intensity values in the output image.

Data Types: double

Output Arguments

J — Adjusted image

grayscale image | RGB image

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

newcmap — Adjusted colormap

c-by-3 numeric matrix

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

C/C++ Code Generation

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

Usage notes and limitations:

• imadjust supports the generation of C code (requires MATLAB^® Coder™). Note that if you choose the generic MATLAB Host Computer target platform, imadjust generates code that uses a precompiled, platform-specific shared library. Use of a shared library preserves performance optimizations but limits the target platforms for which code can be generated. For more information, see Types of Code Generation Support in Image Processing Toolbox.

• When generating code, imadjust does not support indexed images.

GPU Code Generation

Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.

Usage notes and limitations:

• When generating code, imadjust does not support indexed images.

GPU Arrays

Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

This function fully supports GPU arrays. For more information, see Image Processing on a GPU.

Version History

Introduced before R2006a