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I have handwritten notes, with black and red. I color-scanned the notes and made a PDF file. I want to have two very obvious colors in my PDF: black and red. The scanned images contains some near-black colors and some near-red colors, but I just want to make all kinds of near-black colors really black and near-red colors really red. That is, I want to use a colorspace that consists of only black, red, and white (white background).

How can I do this? I have the following software installed:

  • Adobe Acrobat 9
  • Paint.Net
  • Inkscape
  • GIMP
  • ImageMagick
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Do you have white (i.e the background) as well? – ChrisF Oct 19 '11 at 13:45
@ChrisF Oh, yes, I have white background. :) I modified the description. – Chang Oct 19 '11 at 13:53
Thanks - a 3 colour problem is different to a 2 colour problem ;) – ChrisF Oct 19 '11 at 13:59
up vote 1 down vote accepted

One solution and one idea:

Solution: if you can open you PDF with gimp, you can use the "select by color" option, adjust the tolerance, then click over anything red. Afterwards, paint all the selection with red. Then do the same with black. And, finally, select the white background and fill with white.

It'll take a bit long if you have lots os pdfs.

Idea: I'm not sure which format is used by PDF to store your images. If you could re-scan them, do it in .GIF format, or even try to export your PDF as .GIF format. Then, using imageMagick, reduce the color pallete to just 3 possibilities: white, black, red. You won't have the "noise" again.

I'm not sure whether you can do that directly using imageMagick, right from the PDFs.

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Adobe photoshop will open adobe PDF reader docs pretty well usually… – Psycogeek Oct 19 '11 at 15:43
@Psyco :) But I don't work with photoshop, don't know how to select colors, etc, in it... and he didn't said he has a photoshop, just some other programs. – woliveirajr Oct 19 '11 at 15:50
ok i am awake, specifically has 2 "other" paint programs – Psycogeek Oct 19 '11 at 16:13

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