The Image Viewer app is an image display and exploration tool that presents an integrated environment for displaying images and performing common image processing tasks. The Image Viewer provides access to several other tools:
Pixel Information tool — for getting information about the pixel under the pointer
Pixel Region tool — for getting information about a group of pixels
Distance tool — for measuring the distance between two pixels
Image Information tool — for getting information about image and image file metadata
Adjust Contrast tool and associated Window/Level tool — for adjusting the contrast of the image displayed in the Image Viewer and modifying the actual image data. You can save the adjusted data to the workspace or a file.
Crop Image tool — for defining a crop region on the image and cropping the image. You can save the cropped image to the workspace or a file.
Display Range tool — for determining the display range of the image data
In addition, the Image Viewer provides several navigation aids that can help explore large images:
Overview tool — for determining what part of the image is currently visible in the Image Viewer and changing this view.
Pan tool — for moving the image to view other parts of the image
Zoom tool — for getting a closer view of any part of the image.
Scroll bars — for navigating over the image.
The following figure shows the image displayed in the Image Viewer app with many of the related tools open and active.
To start the Image Viewer, click Image Viewer on the
Apps tab, or use the
imtool function. You can also
start another Image Viewer from within an existing Image Viewer by using the New option from the File
To bring image data into the Image Viewer, you can use either the Open or Import from Workspace options from the File menu — see Import Image Data from the Workspace into the Image Viewer App.
You can also specify the name of the MATLAB® workspace variable that contains image data when you call
imtool, as follows:
moon = imread('moon.tif'); imtool(moon)
Alternatively, you can specify the name of the graphics file containing the image. This syntax can be useful for scanning through graphics files.
When you specify a file name, the image data is not stored in a MATLAB workspace variable. To bring the image displayed in the Image Viewer into
the workspace, you must use the
getimage function or the Export to Workspace option from the Image Viewer File menu — see Export Image Data from the Image Viewer App to the Workspace.
The Image Viewer attempts to display an image in its entirety at 100% magnification (one
screen pixel for each image pixel) and always honors any magnification value you specify. If
the image is too big to fit in a figure on the screen, the Image Viewer shows only a portion
of the image, adding scroll bars to allow navigation to parts of the image that are not
currently visible. If the specified magnification would make the image too large to fit on
the screen, the Image Viewer scales the image to fit, without issuing a warning. This is the
default behavior, specified by the
'InitialMagnification' parameter value
To override this default initial magnification behavior for a particular call to
imtool, specify the
For example, to view an image at 150% magnification, use this code.
pout = imread('pout.tif'); imtool(pout, 'InitialMagnification', 150)
You can also specify the
'fit' as the initial magnification value. In
imtool scales the image to fit the default size of a figure
Another way to change the default initial magnification behavior of the Image Viewer is
to set the
ImtoolInitialMagnification toolbox preference. The
magnification value you specify remains in effect until you change it. To set the
iptsetpref or open the Image Processing
Toolbox™ Preferences panel. To open the preferences panel, call
iptprefs or select File > Preferences in the Image Viewer menu. To learn more about toolbox preferences, see
When the Image Viewer scales an image, it uses interpolation to determine the values for screen pixels that do not directly correspond to elements in the image matrix. For more information about specifying an interpolation method, see Resize an Image with imresize Function.
A colormap is a matrix that can have any number of rows, but must have three columns. Each row in the colormap is interpreted as a color, with the first element specifying the intensity of red, the second green, and the third blue.
To specify the color map used to display an indexed image or a grayscale image in the Image Viewer, select the Choose Colormap option on the Tools menu. This activates the Choose Colormap tool. Using this tool you can select one of the MATLAB colormaps or select a colormap variable from the MATLAB workspace.
When you select a colormap, the Image Viewer executes the colormap function you specify and updates the image displayed. You can edit the colormap command in the Evaluate Colormap text box; for example, you can change the number of entries in the colormap (default is 256). You can enter your own colormap function in this field. Press Enter to execute the command.
When you choose a colormap, the image updates to use the new map. If you click OK, the Image Viewer applies the colormap and closes the Choose Colormap tool. If you click Cancel, the image reverts to the previous colormap.
To import image data from the MATLAB workspace into the Image Viewer, use the Import from Workspace option on the Image Viewer File menu. In the dialog box, shown below, you select the workspace variable that you want to import into the workspace.
The following figure shows the Import from Workspace dialog box. You can use the Filter menu to limit the images included in the list to certain image types, i.e., binary, indexed, intensity (grayscale), or truecolor.
To export the image displayed in the Image Viewer to the MATLAB workspace, you can use the Export to
Workspace option on the Image Viewer File
menu. (Note that when exporting data, changes to the display range will not be preserved.)
In the dialog box, shown below, you specify the name you want to assign to the variable in
the workspace. By default, the Image Viewer prefills the variable name field with
BW, for binary images,
RGB, for truecolor images,
I for grayscale or indexed images.
If the Image Viewer contains an indexed image, this dialog box also contains a field where you can specify the name of the associated colormap.
You can also use the
getimage function to bring image data from the
Image Viewer into the MATLAB workspace.
getimage function retrieves the image data
CData) from the current image object. You must use the toolbox
imgca to get the image object displayed in the Image Viewer.
The following example assigns the image data from
moon.tif to the
moon if the figure window in which it is displayed is
moon = getimage(imgca);
To save the image data displayed in the Image Viewer, select the Save
as option from the Image Viewer File menu.
The Image Viewer opens the Save Image dialog box, shown in the following figure. Use this
dialog box to navigate your file system to determine where to save the image file and
specify the name of the file. Choose the graphics file format you want to use from among
many common image file formats listed in the Files of Type menu. If you do not specify a
file name extension, the Image Viewer adds an extension to the file associated with the file
format selected, such as
.jpg for the JPEG format.
Changes you make to the display range will not be saved. If you would like to preserve
your changes, use
To close the Image Viewer, use the Close button in the
window title bar or select the Close option from the Image Viewer
File menu. If you used the
function to start the Image Viewer you can get the figure object that contains the app. You
can use this object to close the app. When you close the Image Viewer, any related tools
that are currently open also close.
Because the Image Viewer does not make its component graphics objects visible, the Image
Viewer does not close when you call the MATLAB
close all command. If you want to close multiple Image Viewers, use the
or select Close all from the Image Viewer File menu.
To print the image displayed in the Image Viewer, select the Print to Figure option from the File menu. The Image Viewer opens another figure window and displays the image. Use the Print option on the File menu of this figure window to print the image. See Print Images for more information.