convert multi-page colour pdfs to high contrast black & white

[stozi]

Hi I want to convert multi-page colour scan-based pdfs to high contrast black & white. I've tried
$ convert input.pdf -level 50%,50% output.pdf
and
$ convert input.pdf -density 300 -level 50%,50% output.pdf

but in both the text in the scans becomes unclear and pixelly. How do I retain the original 'sharpness ' of the text while making this conversion? Thank you.

[fmw42]

try supersampling, by providing a high density before reading the image, then resize afterwards.

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convert -density 288 image.pdf ... your processing ... -resize 25% output.pdf

or just

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convert -density 288 image.pdf ... your processing ... output.pdf

But perhaps you should post an example image and also provide us with your IM version and platform.

Perhaps you want -threshold 50% rather than -level.

[stozi]

ok. I'm on Arch Linux with imagemagick 6.9.2.0-1.
All the pdfs are quite similar to this one, mostly made with the same book-scanner http://vk.com/doc269758631_424827626
I got

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$ convert -density 288 input.pdf -density 300 -threshold 50% output.pdf
convert: unable to extent pixel cache `No such file or directory' @ fatal/cache.c/CacheSignalHandler/3390.

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$ convert -density 288 input.pdf -density 300 -level 50%,50% output.pdf
convert: unable to extent pixel cache `No such file or directory' @ fatal/cache.c/CacheSignalHandler/3390.

[snibgo]

As each page contains a single raster image and nothing else, IM is not the obvious tool to extract the images. A more suitable tool is pdfimages:

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pdfimages -all Gilmour_fascist_italy.pdf gilm

Then process each image as you want.

[stozi]

one by one? I have a few pdfs with over 600 pages. any way to do them as a batch?

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$ convert in.pdf -threshold 50% out.pdf

does the job on a single image.

[fmw42]

mogrify will do a whole folder of images. I suggest you create a new empty directory to hold the output images so you do not write over the originals. Say you have images in folder1 and create an empty folder2


change directory to folder1

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mogrify -path path2/folder2 -format pdf -threshold 50% *.pdf

See http://www.imagemagick.org/Usage/basics/#mogrify

[stozi]

that gave me a complicated fail,

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$ mogrify -path ./ -format pdf -threshold 50% *.pdf
libpng error: Write Error
mogrify: PDFDelegateFailed `[ghostscript library 9.18] -q -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=2 "-sDEVICE=pngalpha" -dTextAlphaBits=4 -dGraphicsAlphaBits=4 "-r72x72"  "-sOutputFile=/tmp/magick-2377mnK6ZlxULIWr%d" "-f/tmp/magick-2377AhoF2ccOVk4y" "-f/tmp/magick-2377UaWJjhh3SCfG"': Error: /VMerror in --showpage--
VM status: 3 12019364 13454248
Current allocation mode is local
Last OS error: 28
GPL Ghostscript 9.18: Unrecoverable error, exit code 1
 @ error/pdf.c/InvokePDFDelegate/271.

but this set of commands seems to work ok

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$ pdfimages -all input.pdf name

$ find . -maxdepth 1 -iname '*jpg' -exec convert -threshold 50% {} ouputdirectory/{} \;

$ mogrify -format pdf -- *.jpg

$ pdfunite *.pdf output.pdf

but can anyone tell my why if try

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find . -maxdepth 1 -iname '*jpg' -exec convert -threshold 50% -format pdf {} ./{} \;

the threshold works but not the format, without giving any error

[fmw42]

libpng error: Write Error

Try changing the delegates.xml file entry for ps (pdf) to pnmraw rather than pngalpha

Or try downgrading GS to at least GS 9.15 (9.16 has been known to have bugs and I do not know about 9.18)


The following seems to work for me. IM 6.9.2.3 Q16 Mac OSX with GS 9.10 and

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<delegate decode="pdf" encode="eps" mode="bi" command=""gs" -q -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=2 "-sDEVICE=epswrite" "-sOutputFile=%o" "-f%i""/>

<delegate decode="pdf" encode="ps" mode="bi" command=""gs" -q -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=2 "-sDEVICE=ps2write" "-sOutputFile=%o" "-f%i""/>

<delegate decode="ps:alpha" stealth="True" command=""gs" -q -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=2 "-sDEVICE=pngalpha" -dTextAlphaBits=%u -dGraphicsAlphaBits=%u "-r%s" %s "-sOutputFile=%s" "-f%s" "-f%s""/>

<delegate decode="ps:cmyk" stealth="True" command=""gs" -q -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=2 "-sDEVICE=pamcmyk32" -dTextAlphaBits=%u -dGraphicsAlphaBits=%u "-r%s" %s "-sOutputFile=%s" "-f%s" "-f%s""/>

<delegate decode="ps:color" stealth="True" command=""gs" -q -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=2 "-sDEVICE=pnmraw" -dTextAlphaBits=%u -dGraphicsAlphaBits=%u "-r%s" %s "-sOutputFile=%s" "-f%s" "-f%s""/>

<delegate decode="ps" encode="eps" mode="bi" command=""gs" -q -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=2 "-sDEVICE=epswrite" "-sOutputFile=%o" "-f%i""/>

<delegate decode="ps" encode="pdf" mode="bi" command=""gs" -q -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=2 "-sDEVICE=pdfwrite" "-sOutputFile=%o" "-f%i""/>

<delegate decode="ps" encode="print" mode="encode" command="lpr "%i""/>

<delegate decode="ps:mono" stealth="True" command=""gs" -q -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=2 "-sDEVICE=pbmraw" -dTextAlphaBits=%u -dGraphicsAlphaBits=%u "-r%s" %s "-sOutputFile=%s" "-f%s" "-f%s""/>

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convert rose: rose: rose: rose: rose: rose.pdf

Then I duplicated it twice and put it into test1 and created an empty test2

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cd test1
mogrify -path ../test2 -format pdf -threshold 50% *.pdf

The results look fine


Also for you last question
convert needs an explicit input image and output image

[snibgo]

... can anyone tell my why if try

find . -maxdepth 1 -iname '*jpg' -exec convert -threshold 50% -format pdf {} ./{} \;

the threshold works but not the format, without giving any error

Because "-format" in convert does something different to "-format" in mogrify. See http://www.imagemagick.org/script/comma ... php#format

[stozi]

Ok, fmw42, that's all way above my head. Anyway, the important thing is I got what I wanted with

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$ pdfimages -all input.pdf name

$ find . -maxdepth 1 -iname '*jpg' -exec convert -threshold 50% {} ouputdirectory/{} \;

$ mogrify -format pdf -- *.jpg

$ pdfunite *.pdf output.pdf

Thank you all.