convolution menu

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This menu is designed to let you perform general linear filtering on images. For example, you might want to average each image pixel with its neighbors, or selectively enhance horizontal image features. These are the sorts of things that you can do with this menu.

The procedure is:

  1. You set the Kernel width and Kernel height fields according to the size of the filter kernel you want to use. For example, if you were averaging a 3 by 3 neighborhood of each image pixel, you would set both fields to 3.
  2. You load the numerical values into the kernel. Negative values are OK, and the software will automatically compensate for unbalanced filters.
  3. You click on the FILTER field to start the filtering process.
  4. You click on the DISPLAY field to see the result of the filtering.

The Auto-stretch? toggle lets you control the normalization of the image after the filter has been applied. If set to Yes, the system will automatically clip 0.05% of the image pixels to black, and 0.05% to white. If set to No, the system will display a histogram of the filtered data, and permit you to set the clipping levels yourself. Since the filtering calculations are carried out to full 16-bit accuracy, you can selectively stretch that portion of the image you are interested in, without losing data to round-off error.

You can also save filter kernels to disk, by clicking on the SAVE FILTER DEFINITION field, or recall them by clicking on the RECALL FILTER DEFINITION field.

You can restrict the filter 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 apply the filter, 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.