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The Sum Function

==================== The Sum function adds the pixel by pixel value of the data contained in the A buffer to the data contained in the B buffer, storing the result in the C buffer. The resulting contents of the C buffer are displayed using the Examine mode. The data in Buffers A and B are unchanged.

Use the Sum function after you have aligned the two images in A and B. If you are going to be adding more than two images, Copy the summed image in C into Buffer B before aligning with the next image to keep all your images registered.

When aligning summed images to single images in this manner, remember that the background threshold will be different between the two images and you will need to set the threshold value each time you switch images.