Viewing Pixel Values with the Pixel Region Tool :: Displaying and Exploring Images (Image Processing Toolbox User's Guide)

Image Processing Toolbox User's Guide

Viewing Pixel Values with the Pixel Region Tool

To view the values of pixels in a specific region of an image displayed in the Image Tool, use the Pixel Region tool. The Pixel Region tool superimposes a rectangle, called the pixel region rectangle, over the image displayed in the Image Tool. This rectangle defines the group of pixels that are displayed, in extreme close-up view, in the Pixel Region tool window.

For example, view an image in the Image Tool.

```
imtool('moon.tif')
```

Start the Pixel Region tool by clicking the Pixel Region button in the Image Tool toolbar or by selecting the Pixel Region option from the Tools menu in the Image Tool. The following figure shows the Image Tool with the Pixel Region tool. For more information about using the Pixel Region tool, see these additional topics:

Image Tool with Pixel Region Tool and Pixel Region Rectangle

Selecting a Region

To examine pixels in specific regions of an image, perform this procedure:

Start the Pixel Region tool by clicking the Pixel Region button in the Image Tool toolbar or by selecting the Pixel Region option from the Tools menu. The Image Tool displays the pixel region rectangle

in the center of the target image and opens the Pixel Region tool.

Note Scrolling the image can move the pixel region rectangle off the part of the image that is currently displayed. To bring the pixel region rectangle back to the center of the part of the image that is currently visible, click the Pixel Region button again. For help finding the Pixel Region tool in large images, see Determining the Location of the Pixel Region Rectangle.

Using the mouse, position the pointer over the pixel region rectangle. The pointer changes to the fleur shape,.
Click the left mouse button and drag the pixel region rectangle to any part of the image. As you move the pixel region rectangle over the image, the Pixel Region tool updates the pixel values displayed. You can also move the pixel region rectangle by moving the scroll bars in the Pixel Region tool window.

Customizing the View

The pixel region rectangle defines the group of pixels that are displayed in the Pixel Region tool. To view a larger region, grab any side of the Pixel Region tool figure window and resize it, or use the zoom tools in the Pixel Region toolbar to zoom in or out on the image.

The Pixel Region tool displays the pixels at high magnification, overlaying each pixel with its numeric value. For RGB images, this information includes three numeric values, one for each band of the image. For indexed images, this information includes the index value and the associated RGB value. If you would rather not see the numeric values in the display, go to the Pixel Region tool Edit menu and clear the Superimpose Pixel Values option.

Pixel Region Tool Edit Menu

Determining the Location of the Pixel Region Rectangle

To determine the current location of the pixel region in the target image, you can use the pixel information given at the bottom of the tool. This information includes the x- and y-coordinates of pixels in the target image coordinate system.

You can also retrieve the current position of the pixel region rectangle by selecting the Copy Position option from the Pixel Region tool Edit menu. This option copies the position information to the clipboard. The position information is a vector of the form [xmin ymin width height].

To paste this position vector into the MATLAB workspace or another application, right-click and select Paste from the context menu.

The following figure shows these components of the Pixel Region tool.

Pixel Region Rectangle Location Information

Printing the View of the Image in the Pixel Region Tool

You can print the view of the image displayed in the Pixel Region tool. Select the Print to Figure option from the Pixel Region tool File menu. See Printing Images for more information.

Getting the Display Range of an Image Getting Information About an Image