pro negative


;+
; NAME:
;	NEGATIVE
;
; PURPOSE:
;	To invert an image containing in a current graphics window. 
;
; CATEGORY:
;	Image display.
;
; CALLING SEQUENCE:
;	NEGATIVE
;
; INPUTS:
;	None
;
; OPTIONAL INPUT PARAMETERS:
;	None.
;
; KEYWORD PARAMETERS:
;	None.
;
; OUTPUTS:
;	None
;	
; COMMON BLOCKS:
;	None.
;
; SIDE EFFECTS:
;	Colors of the image displayed in the current graphics window 
;	are inverted.
;
; RESTRICTIONS:
;	Screen only is supported.
;
; PROCEDURE:
;	The contents of the graphics window is read using TVRD. After
;	that, the inverted array is redisplayed.
;
; MODIFICATION HISTORY:
;	ISTP SD RAS, Nov, 1999.
;	Victor Grechnev (grechnev@iszf.irk.ru):	
;		Initially written.
;-

w = tvrd()

tv, max(w)-w

	end