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Image Viewer app


imtool(I,[low high])
hfigure = imtool(...)
imtool close all


imtool opens the Image Viewer app in an empty state. Use the File menu options Open or Import from Workspace to choose an image for display.

imtool(I) displays the grayscale image I in the Image Viewer.

imtool(I,[low high]) displays the grayscale image I in the Image Viewer, specifying the display range for I in the vector [low high]. The value low (and any value less than low) is displayed as black, the value high (and any value greater than high) is displayed as white. Values in between are displayed as intermediate shades of gray. The Image Viewer uses the default number of gray levels. If you use an empty matrix ([]) for [low high], the Image Viewer uses [min(I(:)) max(I(:))]; the minimum value in I is displayed as black, and the maximum value is displayed as white.

imtool(RGB) displays the truecolor image RGB in the Image Viewer.

imtool(BW) displays the binary image BW in the Image Viewer. Pixel values of 0 display as black; pixel values of 1 display as white.

imtool(X,map) displays the indexed image X with colormap map in the Image Viewer.

imtool(filename) displays the image contained in the graphics file filename in the Image Viewer. The file must contain an image that can be read by imread or dicomread or a reduced resolution dataset (R-Set) created by rsetwrite. If the file contains multiple images, the first one is displayed. The file must be in the current directory or on the MATLAB® path.

hfigure = imtool(...) returns hfigure, a handle to the figure created by the Image Viewer. close(Hfigure) closes the Image Viewer.

imtool close all closes all open Image Viewers.

imtool(...,param1,val1,param2,val2,...) displays the image, specifying parameters and corresponding values that control various aspects of the image display. The following table lists all imshow parameters. Parameter names can be abbreviated, and case does not matter.




2-D, real, m-by-3 matrix specifying the colormap to use for the figure's colormap property. Use this parameter to view grayscale images in false color. If you specify an empty colormap ([]), imtool ignores this parameter.


Two-element vector [LOW HIGH] that controls the display range of a grayscale image. See the imtool(I,[low high]) syntax for more details about how to set this parameter.


Including the parameter name is optional, except when the image is specified by a filename. The syntax imtool(I,[LOW HIGH]) is equivalent to imtool(I,'DisplayRange',[LOW HIGH]). However, the 'DisplayRange' parameter must be specified when calling imtool with a filename, as in the syntax imtool(filename,'DisplayRange',[LOW HIGH]).


Initial magnification used to display the image, specified as 'adaptive', 'fit', or as a numeric scalar value.

When set to 'adaptive', the entire image is visible on initial display. If the image is too large to display on the screen, the Image Viewer displays the image at the largest magnification that fits on the screen.

When set to 'fit', the Image Viewer scales the entire image to fit in the window.

When set to a numeric value, the value specifies the magnification as a percentage. For example, if you specify 100, the Image Viewer displays the image at 100% magnification (one screen pixel for each image pixel).


When the image aspect ratio is such that less than one pixel would be displayed in either dimension at the requested magnification, the Image Viewer issues a warning and displays the image at 100%.

By default, the initial magnification parameter is set to the value returned by iptgetpref('ImtoolInitialMagnification').

Class Support

A truecolor image can be uint8, uint16, single, or double. An indexed image can be logical, uint8, single, or double. A grayscale image can be uint8, uint16, int16, single, or double. A binary image must be logical. A binary image is of class logical.

For all grayscale images having integer types, the default display range is [intmin(class(I)) intmax(class(I))].

For grayscale images of class single or double, the default display range is [0 1]. If the data range of a single or double image is much larger or smaller than the default display range, you might need to experiment with setting the display range to see features in the image that would not be visible using the default display range.

Large Data Support

To view very large TIFF or NITF images that will not fit into memory, you can use rsetwrite to create a reduced resolution dataset (R-Set) viewable in the Image Viewer. R-Sets can also improve performance of the Image Viewer for large images that fit in memory.

The following tools can be used with an R-Set: Overview, Zoom, Pan, Image Information, and Distance. Other tools, however, will not work with an R-Set. You cannot use the Pixel Region, Adjust Contrast, Crop Image, and Window/Level tools. Please note that the Pixel Information tool displays only the x and y coordinates of a pixel and not the associated intensity, index, or [R G B] values.

Related Toolbox Preferences

You can use the Image Processing Preferences dialog box to set toolbox preferences that modify the behavior of the Image Viewer. To access the dialog, select File > Preferences in the MATLAB desktop or Image Viewer menu. Also, you can set preferences programmatically with iptsetpref. The Image Viewer preferences include:

  • 'ImtoolInitialMagnification' controls the initial magnification for image display. To override this toolbox preference, specify the 'InitialMagnification' parameter when you call imtool, as follows:


  • 'ImtoolStartWithOverview' controls whether the Overview tool opens automatically when you open an image using the Image Viewer. Possible values:

    true— Overview tool opens when you open an image.

    {false}— Overview tool does not open when you open an image. This is the default behavior.

For more information about these preferences, see iptprefs.


Display an image from a file.


Display an indexed image.

[X,map] = imread('trees.tif');

Display a grayscale image.

I = imread('cameraman.tif');

Display a grayscale image, adjusting the display range.

h = imtool(I,[0 80]);


imshow is the toolbox's fundamental image display function, optimizing figure, axes, and image object property settings for image display. The Image Viewer provides all the image display capabilities of imshow but also provides access to several other tools for navigating and exploring images, such as the Pixel Region tool, Image Information tool, and the Adjust Contrast tool. The Image Viewer presents an integrated environment for displaying images and performing some common image processing tasks.

You can access the Image Viewer through the Apps tab. Navigate to the Image Processing and Computer Vision group and select Image Viewer.

Introduced before R2006a

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