If no, the image is not displayed. The markzero task aids in the creation of region lists for removal of zeroth-order light from CNOC images. The image cursor is used to mark good and bad regions on the image display. The indicated regions are outlined, with different colors for good and bad regions, and the coordinates are saved on the output file for use with pppfixzero . The user provides the name of the image image on which to locate regions and the name of the output file zerofile to list the bad regions.
Subsequent input is read from the image cursor.
A second valid keystroke completes the definition, and the region is outlined in the specified zerocolor . Pressing any valid key begins the definition of the good region, and a second keystroke ends it. This means that only the x coordinates of the good region input are significant. The region is outlined in red on the image display. The resulting good region is outlined in green.