Convert Grayscale Scanned PDF to Monochrome PDF

[gethmed]

Hi,

I would like to convert scanned PDFs that have greyish backgrounds, into black and white (monochrome) i.e. strictly only two "colors", black (ink or toner) and white (no ink or toner) - all printed characters are black, and the background white (unprinted).

I've tried the process of saving as a TIFF image in Acrobat, with "Monochrome" from the "Colorspace" drop-down menu, but the output was far from ideal.

I wish to avoid
1. exporting / converting a PDF page into an image file, and
2. processing it using other image editing softwares, before
3. re-adding it back into the original PDF,

not just to avoid the hassle, but to avoid any loss in resolution.

Can this be done entirely in Acrobat? 

I've done the conversion to two-tone (black and white) TIFF images on AbbyFine Reader (on a trial of the paid version) with great success and output resolution, but I really hope to do this all-in-one in Acrobat.

If not, am open to other software suggestions. Thanks!

[try67]

See: https://community.adobe.com/t5/acrobat-discussions/convert-pdf-to-100-black-and-white-not-grayscale/...

[gethmed]

Thanks for the link! I've tried both solutions that you posted in that thread. Attaching the raw file and the output files here for your further advice.

13-4_downloaded profile_bw is the output using your GDrive file, "Convert to B&W.kfp".

13-4_bw is the output using the Fixup per your step by step settings.

[try67]

Sorry, I can't help you further. As I wrote in that other thread, this is really a job for an image editing application, not for Acrobat.

[gary_sc]

Hi, @gethmed; I'm sorry, but the problem you're having is that you're trying to fix the problem you (inadvertently) created.

Any photographer will tell you that the more you do in the camera, the less you need to do later to "fix it in Photoshop." The same goes for scanning in preparation for OCR: the more you fix the image at the time of scanning, the less you need to do later in Photoshop, Acrobat, or whatever. By the way, you do NOT want a full 2-bit image (black and white) as that removes the antialiasing that fills out the pixelation that otherwise occurs. You DO want grayscale pixels, just not where you do not want it. 

I go into how to do proper scanning in this blog I wrote for Adobe years ago. The one change that's happened is that software companies continue to offer "one button success" to make it more sellable. Sadly, the more that things are simplified, the harder it is to deal with things that are more challenging.

Nonetheless, I do hope you find your answer here; if you have any questions, please ask.

Good luck!

https://community.adobe.com/t5/adobe-community-professionals/scanning-clean-searchable-pdfs/m-p/4785...

[gethmed]

Thank you for clarifying the difference between 2-bit image and grayscale pixels, + the helpful, detailed post.

With @try67's suggestion I've edited it in Photoshop using Levels adjustment i.e. applying the same concept from your article, that light gray pixels should be considered white.

Yep, still wish and looking forward to the day that will be greater background adjustment controls in Acrobat!