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You can save the contents of the Display Window to a picture file. TkMedit uses the TIFF format, a standard format readable by most image programs. To save a single picture, choose Tools->Save TIFF.... You may want to turn off the cursor or other view items in the View menu before saving your picture.
You can also save a series of images with the Tools->Save TIFF Series... command. This command steps through slices in the current orientation and saves an image of each. You choose a directory and prefix for the file names as well as the range of slices to step through. For example, if you choose /tmp for the directory, image for the prefix, and 5 and 8 for the start and end, it will create /tmp/image005.tiff, /tmp/image006.tiff, /tmp/image007.tiff, and /tmp/image008.tiff.