CLIP will search through the 'source' image and replace all pixels with intensities above MAX with VMAX and all pixels below MIN with VMIN. If VMIN and VMAX are not specified, they default to zero.
If VMIN or VMAX are specified, but no MIN or MAX are not, the routine clips at the values given by VMIN or VMAX. If neither MAX nor VMAX are specified, no upper level clipping will be performed. Similarly, if neither MIN nor VMIN is specified, but MAX or VMAX is, no lower level clipping will be performed.
If no keywords are given, CLIP will set all negative pixels to zero.
You can use the 'BOX=n' keyword to only clip those portions of the image within box 'n'. Multiple boxes can also be specified on the command line to clip within more than one region at a time.
If the MASK keywords is given, a MASK is created (see the MASK command) of the pixels that are being clipped. The related MASKONLY keyword will create a mask without doing the actual clipping. Masks can also be used for clipping with the VMASK=n keyword. All masked pixels will be replaced with the value 'n' in this option. The various MASK options are useful with commands such as the SURFACE command that permit the use of image masks to tag certain pixels before a surface is fit to an image. Note, however, that not all commands recognize masks.
If the RAD=r keyword is used, all pixels within r pixels of the selected pixels will be clipped to the specified value. If the PHOT=r keyword is used, all pixels within r pixels of all the locations on the current VISTA photometry list that satisfy the clipping criteria will be clipped to the values specified with VMAX= and VMIN=. This is a way to clip and/or mask out stars on an image previously identified with the VISTA stellar photometry routines.