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  • Script name: PaperContrast
  • Author: Tintazul
  • Summary: Previous to calling PaperContrast, the user should select a small rectangle of the page background as an indication of what should be whitened out. Script operation: 1. remove transparency (if any); 2. convert to grayscale (if not already); 3. select darkest pixel from selection (if any, sampling max 8 thousand pixels); 4. auto-stretch contrast; 5. set white point to darkest pixel of selection, black point to half of white point; 6. save
#!/usr/bin/env python

from gimpfu import *

def paper_contrast (image, layer):

	max_pixels = 8000		#limits number of pixels to be sampled
	max_blackpoint = 96		#all pixels darker than this will be pure black

	#remove transparency if it has it
	if pdb.gimp_drawable_has_alpha (layer):
		layer = pdb.gimp_image_flatten (image)
	#get format
	#convert to grayscale if not already
	if not pdb.gimp_drawable_is_gray (layer):
		pdb.gimp_image_convert_grayscale (image)

	#collect min pixel from selection
	whitepoint = 255
	(non_empty, x1, y1, x2, y2) = pdb.gimp_selection_bounds (image)
	if non_empty:
		#limit number of pixels to be sampled, in case user made too big a selection
		max_cols = int (max_pixels / (y2-y1+1))
		x2 = min (x2, x1+max_cols-1)

		#collect all pixel values
		for x in range(x1,x2):
			for y in range(y1,y2):
				(channels, pixels) = pdb.gimp_drawable_get_pixel (layer,x,y)
				whitepoint = min (whitepoint, pixels[0])
		#remove selection so that levels options apply to all image

	#auto-strech, then stretch contrast
	pdb.gimp_levels_stretch (layer)
	blackpoint = min (max_blackpoint, int (whitepoint/2))
	print 'blackpoint:', blackpoint, 'whitepoint:', whitepoint
	pdb.gimp_levels (layer, 0, blackpoint, whitepoint, 1.0, 0, 255)

	#update screen, save and remove dirty bit
	pdb.gimp_displays_flush ()
	name = pdb.gimp_image_get_filename(image)
	pdb.gimp_file_save(image, layer, name, name)

	"Increases contrast of a picture with a paper background",
	"Increases contrast of a picture with a paper background. 1) flatten image; 2) convert to grayscale; 3) if there's a selection, get darkest pixel in selection; 4) auto-stretch contrast; 5) stretch levels to make darkest pixel in selection white; 6) save file.",
	"Julio Reis", #very important note: won't allow accented u
	"Julio Reis",