;;;
;;;  autogamma.scm - automatically tweak gamma of dark images
;;;  to look good on my monitor (and maybe elsewhere)
;;;
;;;
;;; --------------------------------------------------------------------
;;; version 0.1  by Jeff Trefftzs <trefftzs@tcsn.net>
;;;     - Initial relase
;;; version 0.2 Raymond Ostertag <r.ostertag@caramail.com>
;;;     - ported to Gimp 2.0
;;; --------------------------------------------------------------------
;;;
;;; This program is free software; you can redistribute it and/or modify
;;; it under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 2 of the License, or
;;; (at your option) any later version.
;;; 
;;; This program is distributed in the hope that it will be useful,
;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;; 
;;; You should have received a copy of the GNU General Public License
;;; along with this program; if not, write to the Free Software
;;; Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

;;; Define the function:

(define (script-fu-autogamma inImage inLayer inMonitor)
  (let* (
	 (histogram (gimp-histogram inLayer
					 HISTOGRAM-VALUE
					 0
					 255))
	 (mean (car histogram))
	 (stdev (cadr histogram))
	 (median (caddr histogram))
	 (pow (/ (- 128 median) 128))	; raise 10 to this power
	 (gamma (* (exp (* pow (log 10))) inMonitor))
	 (gamma (cond (( > gamma 10) 10)
		      (t gamma)))
	 )
    
    (gimp-levels inLayer
		 HISTOGRAM-VALUE
		 0
		 255
		 gamma
		 0
		 255)
    )

  (gimp-displays-flush)
)

(script-fu-register
 "script-fu-autogamma"
 _"<Image>/Script-Fu/Enhance/Gamma Correction..."
 "Corrects an image's gamma by centering the gamma slider under the \
  median value and multiplying the resulting gamma by a monitor-specific \
  constant."
 "Jeff Trefftzs"
 "Copyright 2003, Jeff Trefftzs"
 "ENTER DATE HERE"
 "RGB* GRAY* INDEXED*"
 SF-IMAGE "The Image" 0
 SF-DRAWABLE "The Layer" 0
 SF-ADJUSTMENT "Monitor Correction" '(1.5 .01 10 .1 1 3 1)
)