I have to clean up a large number of images. I have chosen to use unpaper for automatic deskewing. However, since unpaper only accepts pnm images I convert the images to pgm before processing.
This is, however, proving troublesome. Using imagemagick the converted image has a very low quality. If I convert manually using GIMP, the quality is *much* better (while the filesize is significantly smaller).
This is the convert command I use:
convert -verbose ${INPUT} -depth 8 -quality 100 ${BASE}.pgm
Where INPUT contains the name of the pdf file, and BASE the same, but without the extension. I already tried things like resizing to a much larger image, setting quality to 100, nothing seems to do anything.
I also looked into GIMP batch mode. This *should* be able to do what I want, however it seems quite complicated and my feeble attempts to get it to do what I want have failed miserably.
Points will be awarded to the person providing either:
- a imagemagick convert command giving a pgm with the same quality as GIMP can do
- a GIMP batch command creating a good quality pgm.
Some notes: the resulting pgm should be 8 bits. Unpaper will not accept a single bit more.
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changing -quality 100 to -quality 100% does not give any changes in result (the result is bit for bit the same)
-compress None results in an ascii pgm file which is not supported by unpaper
-antialias does not do anything either
The pdf file does not contain text, it is an image coming from one of our scanners,
It basically looks very blocky. I cannot attach the original images since they contain confidential information, but I scanned a random picture.
In the image itself you can see quite a big quality difference, but it is most clear in the text at the top. The jpg file is actually a pgm file, but EE does not appear to accept that extension, so if you use an operating system that depends on file extensions to determine file type you will need to rename it.
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by: JIEXAPosted on 2009-09-08 at 06:05:39ID: 25281409
1. Try to use "-quality 100%" instead of "-quality 100"
2. Try to use "-compress None"
3. Try to use "-antialias"