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Times ago I was not familiar with scanning tools on android like CamScanner or other alternatives, At that time I needed to scan some doc but I did not had a scanner but I had a phone. So I decided to take pictures with the TEXT Mode in phone's stock camera app and join them as a single PDF file. The size was about 700 MB (really high) but i didnt care.
Now I need it on my phone's SD but I dont have that much space on its SD.
I was thinking about extracting pictures from PDF file and enhance them and then make PDF of them.
So my question is: Which tool do I need to do it fast and without trouble?

  • Not a few, as I said its 700MB and has 500 pages ! I want to lower the size too! For your solution if it lowers the size, I can use a Macro. – UltraDEVV Sep 24 '14 at 15:44
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You can enhance the images and remove the gray background using ImageMagick by using auto level and specifying a white threshold:

convert book.pdf -auto-level -white-threshold 70% -quality 100 book2.pdf

You might want to test and calibrate the white threshold value on one page before converting the entire book. Around 70% should work fine. You can also control the file size using the -density and -quality options.

Seeing that your pdf file is huge, this process might take a few minutes to complete, depending on your system

  • Wait! It enhances entire PDF or just image? (it is called imageMagic not PDF one!) I mean can it function inside a PDF file too? (without need of extracting pics?) My system is Core I7 so no problem of speed. – UltraDEVV Sep 24 '14 at 19:50
  • @UltraDEVV it works for pdf files. I tested it on an 80mb book I had, and it took less than a minute. It does not need to extract images from the pdf file, although you can if you want to – Tymric Sep 24 '14 at 19:55
  • Really great. Thanks. Can u estimate the result size? BTW you are in PHD of mechanical engineering at the age of 25? WOW! My country sucks, all are lazy it will take to 30 to get PHD. – UltraDEVV Sep 24 '14 at 19:59
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    @UltraDEVV I can't test it right now since I don't have a large file at my disposal and it also depends on the photos themselves, but my 80mb book became 24mb. If sizes are proportional, then a 700mb file will end up between 200-300. Concerning your other question, thanks, and yes, it's quite common around here. – Tymric Sep 24 '14 at 20:48

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