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More sophisticated image processing

The following are several sophisticated image mode commands for processes such as distortion mapping, bad data etc.:

• FIT looks at rectangular regions within an image to find the positions of peaks. It works by finding a simple centroid, or, by use of /GAUSSIAN, by fitting a 2D gaussian, with some attempt at background subtraction. The /LINE qualifier invokes a centroiding routine appropriate for a linear image such as an arc-line or the direct image of a slit. The output is stored in a CLIST. The regions themselves may be defined in a FIBOX list.

  If the /MASK qualifier is specified then the FIBOX list is created from the positions defined in a MASK list, along with user defined extensions to the slit size, to be taken as the regions. This tool might be used to find the actual positions of the mask slits on a direct image, by looking in a region around where they are expected.

• MAP searches a region of an image for peaks which are the stored in a list slot. A peak is defined as a local maximum, which is above a given threshold, and with all of its immediate neighbours also above the threshold.

  In some cases it might be useful to smooth the image first to minimise noise spikes. For example, MAP could be applied to a matrix image and used in distortion mapping.

• RIDGE maps the positions of ridge-like peaks in the current image. The user defines the direction of the ridges in the spectra (ie. vertical or horizontal centroiding), a threshold and a box width for centroiding.
• SUBSET takes a subset of the current image, by default the current region, and interpolates it to fill the next image slot.
• SQUASH creates a profile of a specified BOX by squashing the data in one direction. By default SQUASH uses a specified box, and adds up the pixels in the direction, producing an XPROF list. Further options are /X, which produces a YPROF list, and /WEIGHT which weights the summation according to the position of the object within the box.
• CUT is similar to SQUASH but works on the current region.