Image Processing Toolbox User's Guide Previous page   Next Page

3. Improve Image Contrast

pout.tif is a somewhat low contrast image. To see the distribution of intensities in pout.tif, you can 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 intensity range is rather narrow. It does not cover the potential range of [0, 255], and is missing the high and low values that would result in good contrast.

The toolbox provides several ways to improve the contrast in an image. One way is to call the histeq function to spread the intensity values over the full range of the image, a process called histogram equalization.

Display the new equalized image, I2, in a new figure window.

Equalized Version of pout.tif

Call imhist again to create a histogram of the equalized image I2. If you compare the two histograms, the histogram of I2 is more spread out than the histogram of I1.

The toolbox includes several other functions that perform contrast adjustment, including the imadjust and adapthisteq functions. See Intensity Adjustment for more information. In addition, the toolbox includes an interactive tool, called the Adjust Contrast tool, that you can use to adjust the contrast and brightness of an image interactively. To start this tool, call the imcontrast function. For more information, see Adjusting the Contrast and Brightness of an Image.

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