Saving PDF files as image files using the Preview application

Question

Saving PDF files as image files using the Preview application

I'm converting PDF files into image files for use with OCR software. The problem is that changing the pixels/inch option from 150 to say 300 does not improve the resolution of the resulting image file. E.g. if I save at 150 p/i and then 300p/i both image files are the same size and resolution. I've tried JPG, JPG-2000, TIFF, and GIF. All produce the same fuzzy result. What am I doing wrong?

MacBook, Mac OS X (10.5.7)

Posted on Aug 2, 2009 11:17 PM

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Answer 1

Aug 2, 2009 11:33 PM in response to Jeffrey Young

How was the PDF created? Does it look sharp? If it contains a low resolution image, you won't be able to get it any sharper.

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Answer 2

Aug 4, 2009 3:16 PM in response to Malcolm Rayfield

The file was produced by a schematic (electronic) editor and has high resolution - vector graphics. It does not contain any images (which have a finite resolution).

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Answer 3

Aug 4, 2009 5:35 PM in response to Jeffrey Young

Are you saving the file as a pixel based file when you save it at 150ppi & then trying to upsize the pixel based file to 300ppi? If so that is your problem. I take it the OCR software will not open a PDF? Do You own a copy of Adobe Illustrator? The pdf files should open in Illustrator with vector files intact. If the file is a pdf & the text has not been turned to outlines why not just copy and paste the text from the pdf doc? Sorry, about all the questions.

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Answer 4

Aug 16, 2009 3:31 PM in response to Jeffrey Young

The schematic file is made up from vector graphics. There are no images embedded in it. For some reason the OCR software (PDF pen) will not recognize the vector drawn characters near the various components. e.g. There may be a resistor with "R5" written next to it. This is the resistors designator. The designator is what I am trying to do the search on. Since PDF pen can perform OCR on scanned (image) documents I thought that turning the PDF schematic into an image file e.g. JPG using Preview would do the trick. Unfortunately as I have already mentioned I can not seem to get Preview to improve the resolution on the resulting image file - the OCR software struggles to recognize any print.

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Answer 5

Sep 16, 2009 7:18 PM in response to Jeffrey Young

Maybe this will work?
http://www.onlineocr.net/default.aspx

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Answer 6

Sep 16, 2009 7:53 PM in response to Jeffrey Young

Do not check resample image box in Preview when changing the resolution.

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