"Peter Desjardins" on wrote...
| I am using Imagemagick to bring scanned images that are in a variety of
| conditions into line with a set of requirements. The images are being
| used by another piece of software that has a maximum allowable file
| size.
|
| I've been trying to get Imagemagick to do three things:
|
| 1. Limit the number of pixels to 150ppi. The scans are of 8.5 inch by
| 11 inch paper
| so we want no more than 1276 x 1650 pixels. These are images of
| forms and they
| only need to be legible, not photo quality.
|
| 2. Remove all color information. Black and white is sufficient.
|
| 3. Convert to GIF.
|
| The source images are in most cases PDF and often 300ppi with color.
| The results I get with the following command are not legible.
|
| convert -resample "150" -monochrome too-big-scan.pdf
| just-right-size.gif
|
| Using Adobe Photoshop and Imageready I can convert the same file to
| 150ppi, black and white GIF and the results are legible (reasonable fax
| quality). This needs to be scripted for people who don't have Photoshop
| though.
|
| Am I choosing the wrong options? Is there a better way to perform this
| task?
Did the image come out the right size?
You could just -resize or -scale the image directly to the right
pixel size needed.
Next, you need to consider cleaning up 'speckles' that may be present
from the scanning process. -despeckle and -median are two such ways.
Another is to blur the image slightly before trying to convert to black
and white.
As for the conversion to black and white....
You can
grey scale the image, then threshold it at an appropriate level,
dithered monocrome,
(which you said came out horible, probably due to the dithering)
two color quantization (dithered or un-dithered)
user supplied colormap reduction.
Just to name a few.
Most of these are exampled in IM Examples, Quantization and Dithering.
http://www.imagemagick.org/Usage/quantize/
And please give us some feedback on your success and failures, and what
you found was the right solution.
For example I would like to add a 'scanning' section to IM examples
but have no small but difficult examples (Say a 100x100 pixel
area cropped from a real scan) to work/play with.
You should have no problem with saving B&W images to GIF, shold work
very well as is.
Anthony Thyssen ( System Programmer ) <[EMAIL PROTECTED]>
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"Mr. Worf, scan that ship." "Aye, Captain... 300 DPI?"
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Anthony's Home is his Castle http://www.cit.gu.edu.au/~anthony/
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