A nondestructive overlay enables you to annotate the display of an image with useful information without actually modifying the image. You can overlay text, lines, points, complex geometric shapes, and bitmaps on top of your image without changing the underlying pixel values in your image; only the display of the image is affected. You can also group several different overlays together to indicate a similarity between the overlays. Overlay groups act as a single overlay and allow you to apply common overlay functions to the entire group, such as clear, copy, and merge. The following figure shows how you can use the overlay to depict the orientation of each particle in the image.

When to Use

You can use nondestructive overlays for many purposes, such as the following:

  • Highlighting the location in an image where objects have been detected.
  • Adding quantitative or qualitative information to the displayed image, such as the match score from a pattern matching function.
  • Displaying ruler grids or alignment marks.

Concepts

Overlays do not affect the results of any analysis or processing functions—they affect only the display. The overlay is associated with an image, so there are no special overlay data types. You need only to add the overlay to your image. By default, Vision clears the overlay anytime you change the size or orientation of the image because the overlay ceases to have meaning. However, you can set the properties for an overlay group so that transformations applied to the image are also applied to the overlay group. You can save overlays with images using the PNG file format.