Image Processing Toolbox

Function Reference

This chapter provides detailed descriptions of the functions in the Image Processing Toolbox. It begins with a list of functions grouped by subject area and continues with the reference entries in alphabetical order.

Functions by Category

The tables below list all functions in the Image Processing Toolbox, plus a few functions in MATLAB that are especially useful for image processing. All of the functions listed have reference entries in this User's Guide, with the following exceptions:

Most MATLAB functions. To see the reference entries for most of the MATLAB functions listed here, see the MATLAB Function Reference. The MATLAB functions imread, imfinfo, and imwrite have entries in this reference because they are essential to image file I/O.

The Image Processing Toolbox demo functions and slideshow functions. For information about any of these functions, see Image Processing Demos in the Preface.

Image Display

colorbar
Display colorbar. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

getimage
Get image data from axes

image
Create and display image object. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

imagesc
Scale data and display as image. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

immovie
Make movie from multiframe indexed image

imshow
Display image

montage
Display multiple image frames as rectangular montage

subimage
Display multiple images in single figure

truesize
Adjust display size of image

warp
Display image as texture-mapped surface

zoom
Zoom in and out of image or 2-D plot. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

Image Display
`colorbar`	Display colorbar. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`getimage`	Get image data from axes
`image`	Create and display image object. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`imagesc`	Scale data and display as image. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`immovie`	Make movie from multiframe indexed image
`imshow`	Display image
`montage`	Display multiple image frames as rectangular montage
`subimage`	Display multiple images in single figure
`truesize`	Adjust display size of image
`warp`	Display image as texture-mapped surface
`zoom`	Zoom in and out of image or 2-D plot. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

Image File I/O

imfinfo
Return information about image file. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

imread
Read image file. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

imwrite
Write image file. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

Image File I/O
`imfinfo`	Return information about image file. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`imread`	Read image file. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`imwrite`	Write image file. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

Geometric Operations

imcrop
Crop image

imresize
Resize image

imrotate
Rotate image

interp2
2-D data interpolation. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

Geometric Operations
`imcrop`	Crop image
`imresize`	Resize image
`imrotate`	Rotate image
`interp2`	2-D data interpolation. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

Pixel Values and Statistics

corr2
Compute 2-D correlation coefficient

imcontour
Create contour plot of image data

imfeature
Compute feature measurements for image regions

imhist
Display histogram of image data

impixel
Determine pixel color values

improfile
Compute pixel-value cross-sections along line segments

mean2
Compute mean of matrix elements

pixval
Display information about image pixels

std2
Compute standard deviation of matrix elements

Pixel Values and Statistics
`corr2`	Compute 2-D correlation coefficient
`imcontour`	Create contour plot of image data
`imfeature`	Compute feature measurements for image regions
`imhist`	Display histogram of image data
`impixel`	Determine pixel color values
`improfile`	Compute pixel-value cross-sections along line segments
`mean2`	Compute mean of matrix elements
`pixval`	Display information about image pixels
`std2`	Compute standard deviation of matrix elements

Image Analysis

edge
Find edges in intensity image

qtdecomp
Perform quadtree decomposition

qtgetblk
Get block values in quadtree decomposition

qtsetblk
Set block values in quadtree decomposition

Image Analysis
`edge`	Find edges in intensity image
`qtdecomp`	Perform quadtree decomposition
`qtgetblk`	Get block values in quadtree decomposition
`qtsetblk`	Set block values in quadtree decomposition

Image Enhancement

histeq
Enhance contrast using histogram equalization

imadjust
Adjust image intensity values or colormap

imnoise
Add noise to an image

medfilt2
Perform 2-D median filtering

ordfilt2
Perform 2-D order-statistic filtering

wiener2
Perform 2-D adaptive noise-removal filtering

Image Enhancement
`histeq`	Enhance contrast using histogram equalization
`imadjust`	Adjust image intensity values or colormap
`imnoise`	Add noise to an image
`medfilt2`	Perform 2-D median filtering
`ordfilt2`	Perform 2-D order-statistic filtering
`wiener2`	Perform 2-D adaptive noise-removal filtering

Linear Filtering

conv2
Perform 2-D convolution. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

convmtx2
Compute 2-D convolution matrix

convn
Perform N-D convolution. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

filter2
Perform 2-D filtering. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

fspecial
Create predefined filters

Linear Filtering
`conv2`	Perform 2-D convolution. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`convmtx2`	Compute 2-D convolution matrix
`convn`	Perform N-D convolution. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`filter2`	Perform 2-D filtering. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`fspecial`	Create predefined filters

Linear 2-D Filter Design

freqspace
Determine 2-D frequency response spacing. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

freqz2
Compute 2-D frequency response

fsamp2
Design 2-D FIR filter using frequency sampling

ftrans2
Design 2-D FIR filter using frequency transformation

fwind1
Design 2-D FIR filter using 1-D window method

fwind2
Design 2-D FIR filter using 2-D window method

Linear 2-D Filter Design
`freqspace`	Determine 2-D frequency response spacing. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`freqz2`	Compute 2-D frequency response
`fsamp2`	Design 2-D FIR filter using frequency sampling
`ftrans2`	Design 2-D FIR filter using frequency transformation
`fwind1`	Design 2-D FIR filter using 1-D window method
`fwind2`	Design 2-D FIR filter using 2-D window method

Image Transforms

dct2
Compute 2-D discrete cosine transform

dctmtx
Compute discrete cosine transform matrix

fft2
Compute 2-D fast Fourier transform. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

fftn
Compute N-D fast Fourier transform. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

fftshift
Reverse quadrants of output of FFT. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

idct2
Compute 2-D inverse discrete cosine transform

ifft2
Compute 2-D inverse fast Fourier transform. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

ifftn
Compute N-D inverse fast Fourier transform. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

iradon
Compute inverse Radon transform

phantom
Generate a head phantom image

radon
Compute Radon transform

Image Transforms
`dct2`	Compute 2-D discrete cosine transform
`dctmtx`	Compute discrete cosine transform matrix
`fft2`	Compute 2-D fast Fourier transform. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`fftn`	Compute N-D fast Fourier transform. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`fftshift`	Reverse quadrants of output of FFT. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`idct2`	Compute 2-D inverse discrete cosine transform
`ifft2`	Compute 2-D inverse fast Fourier transform. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`ifftn`	Compute N-D inverse fast Fourier transform. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`iradon`	Compute inverse Radon transform
`phantom`	Generate a head phantom image
`radon`	Compute Radon transform

Neighborhood and Block Processing

bestblk
Choose block size for block processing

blkproc
Implement distinct block processing for image

col2im
Rearrange matrix columns into blocks

colfilt
Perform neighborhood operations using columnwise functions

im2col
Rearrange image blocks into columns

nlfilter
Perform general sliding-neighborhood operations

Neighborhood and Block Processing
`bestblk`	Choose block size for block processing
`blkproc`	Implement distinct block processing for image
`col2im`	Rearrange matrix columns into blocks
`colfilt`	Perform neighborhood operations using columnwise functions
`im2col`	Rearrange image blocks into columns
`nlfilter`	Perform general sliding-neighborhood operations

Binary Image Operations

applylut
Perform neighborhood operations using lookup tables

bwarea
Compute area of objects in binary image

bweuler
Compute Euler number of binary image

bwfill
Fill background regions in binary image

bwlabel
Label connected components in binary image

bwmorph
Perform morphological operations on binary image

bwperim
Determine perimeter of objects in binary image

bwselect
Select objects in binary image

dilate
Perform dilation on binary image

erode
Perform erosion on binary image

makelut
Construct lookup table for use with applylut

Binary Image Operations
`applylut`	Perform neighborhood operations using lookup tables
`bwarea`	Compute area of objects in binary image
`bweuler`	Compute Euler number of binary image
`bwfill`	Fill background regions in binary image
`bwlabel`	Label connected components in binary image
`bwmorph`	Perform morphological operations on binary image
`bwperim`	Determine perimeter of objects in binary image
`bwselect`	Select objects in binary image
`dilate`	Perform dilation on binary image
`erode`	Perform erosion on binary image
`makelut`	Construct lookup table for use with `applylut`

Region-Based Processing

roicolor
Select region of interest, based on color

roifill
Smoothly interpolate within arbitrary region

roifilt2
Filter a region of interest

roipoly
Select polygonal region of interest

Region-Based Processing
`roicolor`	Select region of interest, based on color
`roifill`	Smoothly interpolate within arbitrary region
`roifilt2`	Filter a region of interest
`roipoly`	Select polygonal region of interest

Colormap Manipulation

brighten
Brighten or darken colormap. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

cmpermute
Rearrange colors in colormap

cmunique
Find unique colormap colors and corresponding image

colormap
Set or get color lookup table. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

imapprox
Approximate indexed image by one with fewer colors

rgbplot
Plot RGB colormap components. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

Colormap Manipulation
`brighten`	Brighten or darken colormap. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`cmpermute`	Rearrange colors in colormap
`cmunique`	Find unique colormap colors and corresponding image
`colormap`	Set or get color lookup table. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`imapprox`	Approximate indexed image by one with fewer colors
`rgbplot`	Plot RGB colormap components. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

Color Space Conversions

hsv2rgb
Convert HSV values to RGB color space. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

ntsc2rgb
Convert NTSC values to RGB color space

rgb2hsv
Convert RGB values to HSV color space. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

rgb2ntsc
Convert RGB values to NTSC color space

rgb2ycbcr
Convert RGB values to YCbCr color space

ycbcr2rgb
Convert YCbCr values to RGB color space

Color Space Conversions
`hsv2rgb`	Convert HSV values to RGB color space. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`ntsc2rgb`	Convert NTSC values to RGB color space
`rgb2hsv`	Convert RGB values to HSV color space. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`rgb2ntsc`	Convert RGB values to NTSC color space
`rgb2ycbcr`	Convert RGB values to YCbCr color space
`ycbcr2rgb`	Convert YCbCr values to RGB color space

Image Types and Type Conversions

dither
Convert image using dithering

double
Convert data to double precision. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

gray2ind
Convert intensity image to indexed image

grayslice
Create indexed image from intensity image by thresholding

im2bw
Convert image to binary image by thresholding

im2double
Convert image array to double precision

im2uint16
Convert image array to 16-bit unsigned integers

im2uint8
Convert image array to 8-bit unsigned integers

ind2gray
Convert indexed image to intensity image

ind2rgb
Convert indexed image to RGB image

isbw
Return true for binary image

isgray
Return true for intensity image

isind
Return true for indexed image

isrgb
Return true for RGB image

mat2gray
Convert matrix to intensity image

rgb2gray
Convert RGB image or colormap to grayscale

rgb2ind
Convert RGB image to indexed image

uint16
Convert data to unsigned 16-bit integers. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

uint8
Convert data to unsigned 8-bit integers. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

Image Types and Type Conversions
`dither`	Convert image using dithering
`double`	Convert data to double precision. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`gray2ind`	Convert intensity image to indexed image
`grayslice`	Create indexed image from intensity image by thresholding
`im2bw`	Convert image to binary image by thresholding
`im2double`	Convert image array to double precision
`im2uint16`	Convert image array to 16-bit unsigned integers
`im2uint8`	Convert image array to 8-bit unsigned integers
`ind2gray`	Convert indexed image to intensity image
`ind2rgb`	Convert indexed image to RGB image
`isbw`	Return true for binary image
`isgray`	Return true for intensity image
`isind`	Return true for indexed image
`isrgb`	Return true for RGB image
`mat2gray`	Convert matrix to intensity image
`rgb2gray`	Convert RGB image or colormap to grayscale
`rgb2ind`	Convert RGB image to indexed image
`uint16`	Convert data to unsigned 16-bit integers. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)
`uint8`	Convert data to unsigned 8-bit integers. (This is a MATLAB function. See the online MATLAB Function Reference for its reference page.)

Toolbox Preferences

iptgetpref
Get value of Image Processing Toolbox preference

iptsetpref
Set value of Image Processing Toolbox preference

Toolbox Preferences
`iptgetpref`	Get value of Image Processing Toolbox preference
`iptsetpref`	Set value of Image Processing Toolbox preference

Demos

dctdemo
2-D DCT image compression demo

edgedemo
Edge detection demo

firdemo
2-D FIR filtering and filter design demo

imadjdemo
Intensity adjustment and histogram equalization demo

nrfiltdemo
Noise reduction filtering demo

qtdemo
Quadtree decomposition demo

roidemo
Region-of-interest processing demo

Demos
`dctdemo`	2-D DCT image compression demo
`edgedemo`	Edge detection demo
`firdemo`	2-D FIR filtering and filter design demo
`imadjdemo`	Intensity adjustment and histogram equalization demo
`nrfiltdemo`	Noise reduction filtering demo
`qtdemo`	Quadtree decomposition demo
`roidemo`	Region-of-interest processing demo

Slide Shows

ipss001
Region labeling of steel grains

ipss002
Feature-based logic

ipss003
Correction of nonuniform illumination

Slide Shows
`ipss001`	Region labeling of steel grains
`ipss002`	Feature-based logic
`ipss003`	Correction of nonuniform illumination

Reference Alphabetical List of Functions