; 210_contrast_auto-contrast.scm
; last modified/tested by Paul Sherman [gimphelp.org]
; Wednesday, 07/01/2020 on GIMP 2.10.20
;==================================================
;
; Installation:
; This script should be placed in the user or system-wide script folder.
;
;	Windows 7/10
;	C:\Program Files\GIMP 2\share\gimp\2.0\scripts
;	or
;	C:\Users\YOUR-NAME\AppData\Roaming\GIMP\2.10\scripts
;	
;    
;	Linux
;	/home/yourname/.config/GIMP/2.10/scripts  
;	or
;	Linux system-wide
;	/usr/share/gimp/2.0/scripts
;
;==================================================
;
; LICENSE
;
;    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 3 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, see <http://www.gnu.org/licenses/>.
;
;==============================================================
; Original information 
;
; Automatically adjusts contrast of the current
; drawable by duplicating the layer, setting the
; new layer to Value blend mode, then running
; Auto Levels on the Value layer.
;==============================================================
(define (210-auto-contrast 
		img 
		drawable 
		merge-flag
	)
	(gimp-image-undo-group-start img)
	(if (not (= RGB (car (gimp-image-base-type img))))
			 (gimp-image-convert-rgb img))   
   ; Create a new layer
   (define value-layer (car (gimp-layer-copy drawable 0)))
   ; Give it a name
   (gimp-item-set-name value-layer "Contrast Adjustment Layer")
   ; Add the new layer to the image
   (gimp-image-insert-layer img value-layer 0 0)
   ; Set opacity to 100%
   (gimp-layer-set-opacity value-layer 100)
   ; Set the layer mode to Value
   (gimp-layer-set-mode value-layer 14)
   ; Adjust contrast
   (gimp-levels-stretch value-layer)
   ; Merge down, if required
   (if (equal? merge-flag TRUE)
       (gimp-image-merge-down img value-layer 1 )
       ()
   )
   (gimp-image-undo-group-end img)
   (gimp-displays-flush)   
)
(script-fu-register "210-auto-contrast"
	"Auto Contrast"
	"Automatically adjust contrast of drawable"
	"Mark Lowry"
	"Mark Lowry"
	"2006"
	"*"
	SF-IMAGE 	"Image" 		0
	SF-DRAWABLE "Current Layer" 0
	SF-TOGGLE 	"Merge Layers?" FALSE
 )
(script-fu-menu-register "210-auto-contrast" "<Image>/Script-Fu/Contrast")