Basic Image Import, Processing, and Export

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 I . 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.

imshow(I)

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 uint8 data.

whos
  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.

figure
imhist(I)

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 imadjust and adapthisteq, and interactive tools such as the Adjust Contrast tool, available in the Image Viewer.)

I2 = histeq(I);
figure
imshow(I2)

Call the 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 I .

figure
imhist(I2)

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

View what 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.

imfinfo('pout2.png')
ans = 

                  Filename: '/tmp/Bdoc14b_152206_2461/tp3b323b87_55cd_4890...'
               FileModDate: '20-Sep-2014 02:19:25'
                  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: '20 Sep 2014 06:19:25 +0000'
                     Title: []
                    Author: []
               Description: []
                 Copyright: []
              CreationTime: []
                  Software: []
                Disclaimer: []
                   Warning: []
                    Source: []
                   Comment: []
                 OtherText: []

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