From: Steven Lumos <steven@...>
Date: 2007-10-02T04:12:18+09:00
Subject: Re: Cut pages for OCR with RMagick?

Tim Hunter <TimHunter@nc.rr.com> writes:

> Axel Etzold wrote:
>
>> I have tried to convert my pages, which are A4 and 600 dpi, to pixel arrays,
>> but this is quite slow. Is there a better method, ie. using to_blob ?
>
> to_blob just gives you an in-memory copy of the image file. If the
> image is in JPG format, for example, then the blob is an in-memory JPG
> file. So, there's no help there.
>
> Ideally you could use some RMagick method or combination of methods to
> accomplish your goal. Since the ImageMagick/GraphicsMagick routines
> are written in C they'd be much faster. Offhand I can't think of any
> such methods, but then I'm not very clever at that sort of thing.
>
> You might try asking the ImageMagick gurus
> (http://www.imagemagick.org/discourse-server/) if there's a way to do
> it with the command-line utilities. If so, you can usually translate
> the commands and options into RMagick methods. See
> http://www.simplesystems.org/RMagick/doc/optequiv.html for help with
> that.
>
> -- 
> RMagick OS X Installer [http://rubyforge.org/projects/rmagick/]
> RMagick Hints & Tips [http://rubyforge.org/forum/forum.php?forum_id=1618]
> RMagick Installation FAQ [http://rmagick.rubyforge.org/install-faq.html]

When it comes to document imaging, the problem with most image
processing kits, including/especially ImageMagick, is that they insist
on using a 32-bit per pixel memory representation for all images.
Fine for your 200x200 web GIF, but No Fun when your ~4MB B&W scanned
page suddenly expands to 140MB in memory.

You can try NArray[1] (8x expansion is better the 32x), or use a kit
that can handle 1-bit images in memory, e.g. Leptonica[2].

Steve

[1] http://narrary.rubyforge.org/
[2] http://www.leptonica.com/