is_compressed.i4.v = chkcmp(vun.i2.r, record_number.i4.r,
				    rows.i4.r, columns.i4.r)

	This routine will check a file record to see if it is a compressed
	TV image.  If it is, the number of rows and columns that make up
	the image will be returned.  The file must have been opened before
	calling this routine.

	vun		VUN for previously opened file
	record_number	record number of image to check
	rows		number of rows in image
	columns		number of columns in image

	This function returns status values as follows:

	FALSE			record does not contain a compressed image
	otherwise		length of the compressed image in bytes

	This function requires the following include files:

	cnsparam_h, cbslib_h

	Related functions:

	window_tvdisp(_c), window_tvsave_c, fm_open(_c)