b w illumination menu

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False Illumination is a technique that lets you selectively enhance image features. It is especially useful for bringing out details in smooth, relatively featureless images.

To understand false illumination, you have to think of the image as a three-dimensional surface. Imagine that your image is a special kind of contour map, where elevation is indicated by intensity rather than contour lines. That is, places that are dark represent low elevations, and lighter grey shades represent higher altitudes. In this scheme, the image would represent a surface, with hills and valleys. Now suppose you made a plaster of paris model of the surface, and shone a light on it at an angle. Your light would illuminate some areas of the image and other areas would be in shadow. False illumination lets you do this with the computer, and see what the result would look like.

To see how false illumination can be useful, go back to the plaster model. Suppose you had such a model, and it was very nearly flat, but you suspected some imperceptible ridges were on the surface. If you shone your light at a very low angle, almost horizontally, you could make even the slightest of bumps show up. Similarly, false illumination can be used to enhance very small deviations in image intensity.

The procedure for using false illumination is:

  1. Adjust the "position" of your light source by setting the Elevation angle and Azimuth angle menu fields. The elevation angle is how far above the horizon the light would appear to someone standing on the surface of the image. The azimuth angle it the compass direction in which the light is pointed, with zero=north.
  2. Click on the CALCULATE IMAGE menu field. This creates the falsely-illuminated image.
  3. To see the results, click on the DISPLAY IMAGE menu field.

You can restrict the processing to work on only a portion of the image by specifying an Area of Interest (AOI). The AOI can be either rectangular or polygonal. To specify a rectangular AOI, first display the image, then click on USE RECTANGULAR AREA. The system will prompt you to indicate the rectangular area on the image. Do so with two clicks. When you then initiate the processing, only the pixels in the rectangular area will be affected. Similarly, you can make an irregular AOI by first clicking on USE POLYGONAL AREA and then outlining the AOI with a series of clicks on mouse button 1. Terminate the drawing of the AOI by clicking with button 2. If you have restricted processing to an AOI and you want to make it apply to the entire image again, click on USE ENTIRE IMAGE.