This example shows how to read an image into the workspace, adjust the contrast in the image, and then write the adjusted image to a file.
Step 1: Read and Display an Image
First, clear the workspace of any variables and close open figure windows.
clear close all
Read an image into the workspace, using the
imread command. The example reads one of the sample images included with the toolbox, an image of a young girl in a file named
pout.tif , and stores it in an array named
imread infers from the file that the graphics file format is Tagged Image File Format (TIFF).
I = imread('pout.tif');
Display the image, using the
imshow function. You can also view an image in the Image Viewer app. The
imtool function opens the Image Viewer app which presents an integrated environment for displaying images and performing some common image processing tasks. The Image Viewer app provides all the image display capabilities of
imshow but also provides access to several other tools for navigating and exploring images, such as scroll bars, the Pixel Region tool, Image Information tool, and the Contrast Adjustment tool.
Step 2: Check How the Image Appears in the Workspace
Check how the
imread function stores the image data in the workspace, using the
whos command. You can also check the variable in the Workspace Browser. The
imread function returns the image data in the variable
I , which is a 291-by-240 element array of
Name Size Bytes Class Attributes I 291x240 69840 uint8
Step 3: Improve Image Contrast
View the distribution of image pixel intensities. The image
pout.tif is a somewhat low contrast image. To see the distribution of intensities in the image, create a histogram by calling the
imhist function. (Precede the call to
imhist with the figure command so that the histogram does not overwrite the display of the image
I in the current figure window.) Notice how the histogram indicates that the intensity range of the image is rather narrow. The range does not cover the potential range of [0, 255], and is missing the high and low values that would result in good contrast.
Improve the contrast in an image, using the
histeq function. Histogram equalization spreads the intensity values over the full range of the image. Display the image. (The toolbox includes several other functions that perform contrast adjustment, including
adapthisteq, and interactive tools such as the Adjust Contrast tool, available in the Image Viewer.)
I2 = histeq(I); figure imshow(I2)
imhist function again to create a histogram of the equalized image
I2 . If you compare the two histograms, you can see that the histogram of
I2 is more spread out over the entire range than the histogram of
Step 4: Write the Adjusted Image to a Disk File
Write the newly adjusted image
I2 to a disk file, using the
imwrite function. This example includes the filename extension
'.png' in the file name, so the
imwrite function writes the image to a file in Portable Network Graphics (PNG) format, but you can specify other formats.
imwrite (I2, 'pout2.png');
Step 5: Check the Contents of the Newly Written File
imwrite wrote to the disk file, using the
imfinfo function. The
imfinfo function returns information about the image in the file, such as its format, size, width, and height.
ans = Filename: '/tmp/Bdoc15a_200152_161220/tpf05ecb51_9f0a_4e...' FileModDate: '23-Feb-2015 09:38:29' FileSize: 36938 Format: 'png' FormatVersion:  Width: 240 Height: 291 BitDepth: 8 ColorType: 'grayscale' FormatSignature: [137 80 78 71 13 10 26 10] Colormap:  Histogram:  InterlaceType: 'none' Transparency: 'none' SimpleTransparencyData:  BackgroundColor:  RenderingIntent:  Chromaticities:  Gamma:  XResolution:  YResolution:  ResolutionUnit:  XOffset:  YOffset:  OffsetUnit:  SignificantBits:  ImageModTime: '23 Feb 2015 14:38:29 +0000' Title:  Author:  Description:  Copyright:  CreationTime:  Software:  Disclaimer:  Warning:  Source:  Comment:  OtherText: