NAME:
	diffmag_izrgu
 PURPOSE:
       this program makes differential magnitude plots of objects from a 
	'izrgu' database produced from a merged file for different 
	classifications, for each ccd. 
	Only does i-band currently
	It produces a ps file or 5 gif files or outputs to screen
 CALLING SEQUENCE:
	diffmag_izrgu,wfcdb,wfc_image[,ps=ps,gif=gif,col=col]
 INPUTS:
	wfcdb:The wfc database to be searched. Must start with 'dbase/... '
	wfc_image: the image 
 OPTIONAL OUTPUT KEYOWRDS:
	ps: root file name of the 4 output ps files 
		(will have ps1.ps,ps2.ps,etc....)
	gif:root file name of the 16 output gif files. Only active if ps is 
		not set. (will have gif_1_all.gif, gif_1_stars.gif,...)
	If neither set the output is sent to an IDL graphics window
	field: STRING: name of field ie directory where the wfc/ dir is
 EXAMPLE:
	diffmag_izrgu,'wfc','r219698'[,ps='diff_i_wfc']
 CALLED PROCEDURES:
	astrolib procedures,select_classes,wcs_zpn,mk_plot_diff
 MODIFICATION HISTORY:
	31-Oct-2000  Original by Suzanne Aigrain
	09-Nov-2000  S. Aigrain: adapt to merged db

(See /home/xmmssc/soft/idl/pro/wfcqc/diffmag_izrgu.pro)