Get Started with Image Viewer App

The Image Viewer app presents an integrated environment for displaying images and performing common image processing tasks. The workflow for using Image Viewer typically involves a combination of these steps:

• Open the app and read an image.

• Navigate the image.

• Get information about the image data.

• Modify the image data.

• Save and export results.

The figure shows an image displayed in Image Viewer, highlighting the contrast adjustment, colormap, and pixel values view options.

Note

You can access individual tools outside the Image Viewer app. To do so, display an image in a figure window by using a function such as imshow, and then create one or more tools using toolbox functions. You can build an image processing app with custom layout and behavior using a combination of individual tools. For more information, see Interactive Image Viewing and Processing Tools.

Open Image Viewer App

You can open the Image Viewer app programmatically or from the MATLAB^® toolstrip. In both cases, you can load an image from a workspace variable or from a file. Image Viewer can open any file that the imread function can read, plus formats such as DICOM, NITF, and RAW.

• Open the Image Viewer app from the command line by using the imageViewer function. Use this function when you want to specify the image to display upon opening, as well as control various aspects of the initial image display, such as the initial magnification, colormap, or display range, by using name-value arguments. For example, this code opens Image Viewer and displays the image with filename cameraman.tif at 200% of the original image dimensions.

  imageViewer("cameraman.tif",InitialMagnification=200)

• Open the Image Viewer app from the Apps tab of the MATLAB toolstrip, under Image Processing and Computer Vision. To import an image from a file, on the Viewer tab of the app toolstrip, select Import Image > From File. To import image data from the workspace, click the import button or select Import Image > From Workspace. Select the image you want to import from the dialog box and click OK.

  

Navigate Image in Image Viewer App

After you open Image Viewer and import an image, you can use navigation aids and tools to explore the image in detail.

Action	Tools and Navigation Aids	Example
See image overview	An image overview helps you navigate a zoomed in image. To open the Overview pane, on the Viewer tab of the app toolstrip, select Image Overview. The Overview pane displays the entire image with a rectangle that indicates which portion of the image is currently visible in the main display pane. You can pan the image in the main display by moving the rectangle in the Overview pane.
Magnify image	Zoom in and out using the mouse scroll wheel. You can also zoom in or out by pressing Ctrl+Plus or Ctrl+Minus keys, respectively. When Image Viewer scales an image, it uses interpolation to determine the values for screen pixels that do not directly correspond to pixel elements in the image matrix. You can change the interpolation method in the app toolstrip under Interpolation Method. Select nearest to view image data as a grid of pixel elements, such as when viewing pixel values. Select bilinear to view smoothed pixel intensities without visible pixel elements. For more information about the interpolation methods used for resizing images, see imshow.
Pan image	To pan an image that is too large to fit in the Image Viewer window, use the arrow keys or the Overview pane. Alternatively, in the top-right corner of the main display pane, select Pan , and then drag the image to move around.
Choose image colormap	To enhance the visibility of features in grayscale and indexed images, you can change the image colormap on the Colormap tab of the app toolstrip. You can select a predefined MATLAB colormap such as jet or parula, or a colormap variable from the workspace. You can also create a colormap by entering a MATLAB expression that, when evaluated, generates an m-by-3 colormap. Note The Colormap tab is not available for RGB images.

Get Information About Image Data

Image Viewer provides information about pixel values and other aspects of the image data. These tools are all available on the Viewer tab of the app toolstrip.

Information	Description	Example
Image metadata	View information about the image by selecting Image Metadata in the app toolstrip. The app provides basic information about the width, height, number of color channels, data type, and image type of the image. If you load an image from a file, then the app also displays the file metadata. This metadata is the same information returned by the information function for that file format, such as the imfinfo, dicominfo, rawinfo, or nitfinfo function.
Pixel information	When you pause the mouse pointer on a pixel, the bottom-left corner of the main display pane shows the xy-coordinates and value of that pixel. For more information, see Determine Individual Pixel Values in Image Viewer.
Pixel values	When you zoom far enough into the image, the app superimposes the pixel values on the image in the main display pane. For more information, see View Pixel Values in Image Region. To view pixel values, zoom in on the image and, on the Viewer tab of the app toolstrip, select Show Pixel Value. You can manually zoom in until the pixel values appear, or, in the drop-down menu in the Zoom section of the app toolstrip, select Zoom To Pixels. When viewing pixel values, in the Viewer tab of the app toolstrip, set Interpolation Method to nearest.
Image height and width	The bottom-right corner of the main display pane shows the height and width of the image, in pixels.
Measure distance or area	Measure the Euclidean distance between two pixels, or the area within a polygon. For more information, see Measure Distances and Areas Using Image Viewer App

Modify Image Data

Using Image Viewer, you can adjust image contrast and crop an image.

By default, when you close Image Viewer, the app does not save the modified image data. However, you can export the modified image to a file or save the modified data in a workspace variable. For more information, see Save and Export Results.

Modification	Description	Example
Adjust contrast	Adjust the contrast of grayscale images, on the Contrast tab of the app toolstrip, by using an interactive histogram, or by entering values for the window bounds, window width, and window center. For more information, see Adjust Image Contrast in Image Viewer App. Note The Contrast tab is not available for RGB or binary images.
Crop image	To crop an image to a rectangular region of interest, on the Viewer tab of the app toolstrip, select Crop Image. For more information, see Crop Image Using Image Viewer App.

Save and Export Results

Image Viewer enables you to export image data to the workspace or save image data to a file. The exported image data includes any cropping or contrast adjustment changes you perform in the app. The exported image does not include any colormap changes. The exported image has the same number of channels and is of the same data type as the imported image. You can also export area and distance measurements to the workspace.

Action	Description	Example
Export image as workspace variable	On the Viewer tab of the app toolstrip, click the export button or select Export > Export Image > To Workspace. In the Export To Workspace dialog box, specify a workspace variable name, and click OK.
Save image to file	On the Viewer tab of the app toolstrip, select Export > Export Image > To Image File. In the Save Image To File dialog box, navigate to the location where you want to save the image file. Specify a filename and format, and click Save.
Export measurements to workspace	On the Viewer tab of the app toolstrip, select Export > Export Measurements. In the Export To Workspace dialog box, select which measurements to export and specify a variable name for each measurement. Then, click OK.