Use this filter to measure the distance between objects. The distances will be coded in gray values. With a binary image the object is white against a black background.
You'll find the Distance Dark filter in the Process > Morphological Filter menu.
Before using the filter
This filter can only be applied to binary images. Therefore, you have to first binarize the image by using the Image > Mode > Binary... command. Otherwise, in the menu for morphological filters, the Distance Dark command is grayed out. You can find more information on binarizing here.
Resulting images
Even if the source image is a binary image, the resulting image is always a gray value image. For this reason, in the dialog box for image processing operations, a message appears at the bottom left when you have clicked the Apply button.
See also
Overview - Morphological Filter
Working with morphological filters
Settings for the filter
The dialog box that is opened when you use an image processing operation is made up in the same way for every operation. Click here to switch to a description of this dialog box.
Application
The Distance Dark filter is often applied as a preprocessing step. With this filter, you can for example analyze the distances between objects.
The way the Distance filter works can be demonstrated on a simple binary image. You'll find the source image (1) on the left-hand side. With the Distance Dark (2) filter, the black image segment is interpreted as an image object and is then coded in gray values, just like the Distance Bright filter. The example also shows that the edge of the image is interpreted as the edge of the object. In the resulting image, the object from the original image is black.
Exactly what happens?
The way the Distance Dark filter works is exactly the same as the way the Distance Bright filter works. The resulting images of both filters are the same if they are applied to two images with inverse contrast.
The resulting image may possibly appear black. In this case, the objects are so small that the filter has only assigned the pixels low gray values for a short distance from the edge of the object. In this case, optimize the image contrast.
Optimizing image contrast
1.Use the View > Tool Windows > Adjust Display command to make the Adjust Display tool window appear.
2.Select the Auto Contrast option in the Histogram group.
3.Click the Search button.
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