[snip] > I have tried converting the files to B/W TIFF myself, using Gimp. But > no matter how much I fiddle around with contrast settings, etc., the > black and white images are pathetic. I cannot believe that conversion of > grayscale images to black/white cannot be better than this. > > Any recommendations from others who have already gone through this agony? > How can we improve the input images of OCR programs like tesseract? [snip]
hi sandeep, long time! :-) howto improve grayscale images while converting them to black&white: a) using brightness/contrast is a quick and not so efficient method, as you've discovered. b) use the 'levels' command. the histogram that shows up allows you to choose what should be considered black, and what should be considered white. so anything lighter than the 'white' you choose also becomes white, and anything darker than the 'black' you choose also becomes black. the grayscale in the middle allows you to choose what will be neutral grey. don't worry, it's a playful thing, just drag around with your mouse on all the settings in 'levels' and you'll see how it dramatically alters the image. c) 'posterize' is another in-between step. it reduces grayscale of 256 shades, to far less shades, which is the equivalent of enhancing contrast. d) play around with 'curves' which also dramatically alters tonality. think of 'curves' as a graphic equalizer normally used on a stereo system, used for visual images. e) more advanced techniques call for using 'chops' which stand for channel operations, first hacked together by kai krause. oh! i could go on with several dozen more creative hacks for enhancing contrasts! i recall when long ago i used to conduct workshops around 'digital image-editing' i'd spend about 2 hours just explaining all the techniques around this one single topic. it is really quite fascinating! but am sure the above could help you out with your problem. see ya around at one of our LUG or similar meets, buddy. :-) niyam bhushan _______________________________________________ ilugd mailinglist -- ilugd@lists.linux-delhi.org http://frodo.hserus.net/mailman/listinfo/ilugd Archives at: http://news.gmane.org/gmane.user-groups.linux.delhi http://www.mail-archive.com/ilugd@lists.linux-delhi.org/
