It is a common situation for the user to want to process a limited subset
of an image. It is also common for an image to contain pixels which are
``blanked'' or have an ``undefined value''. Miriad routines are available to
treat these two pixel selection operations together. The input to these
routines are the task parameters which describe the subregion the user
is interested in, and a masking item that may be associated with an image.
The output is a description of the pixels selected.
Region of Interest and Pixel Blanking
Each image dataset may have a masking item. This
is a bitmap containing a flag for each pixel, indicating
whether the pixel is good or bad. For bad pixels, the pixel value actually
in the image is not defined, though it will be a legal or typical value.
Zero, or the value of the pixel before blanking, is a good choice.