Image operations are procedures carried out with entire images. They include mathematical operations (addition, subtraction, multiplication, division, merge), rank operations (minimum, median, maximum), calibration (dark subtraction and flat-fielding), plus methods used to compare (blinking) and combine (track-and-stack averaging) images. Their value stems from allowing the user to create even more powerful procedures by combining point, linear, and nonlinear operators. This chapter details how those image operations are carried out.
Before going on, let us again clarify the words "image" and "frame." Both words refer to image data. A set of data that shows the bias offset, dark current, or the flat-field of the CCD is sometimes called a "frame," while a set of data that shows an object is almost always called an image. The difference is purely one of terminology: there is no intrinsic difference in how the image data are stored or processed.
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