How to downsample images within PDF file?

Question

Need a Java-based solution or, at the worst, command-line for Linux.

I tried to use Ghostscript:

gs -sDEVICE=pdfwrite -dPDFA -dBATCH -dNOPAUSE -dUseCIEColor \    -sProcessColorModel=DeviceCMYK -sPDFACompatibilityPolicy=1 \    -sOutputFile=downgraded.pdf leon_range_my12_w22_brochure.pdf 

but I got a lot of errors...

Answer 1

Here's an example of how you can downsample all (color, gray and mono) images to 72dpi with a Ghostscript commandline:

gs \   -o downsampled.pdf \   -sDEVICE=pdfwrite \   -dDownsampleColorImages=true \   -dDownsampleGrayImages=true \   -dDownsampleMonoImages=true \   -dColorImageResolution=72 \   -dGrayImageResolution=72 \   -dMonoImageResolution=72 \   -dColorImageDownsampleThreshold=1.0 \   -dGrayImageDownsampleThreshold=1.0 \   -dMonoImageDownsampleThreshold=1.0 \    input.pdf 

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Update:
The *ImageDownsampleThreshold=1.0 parameters enforce that all Images with a resolution higher than the target resolution of 72 dpi will be downsampled. If this parameter is not given (or set to a different value), the default values will be used: *ImageDownsampleThreshold=1.5. This default value will only downsample images with a value of 108 dpi (or higher) and leave the other ones untouched.

Answer 2

This is what I am using:

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH -sOutputFile=OUTPUT.pdf INPUT.pdf

For your reference:

-dPDFSETTINGS=/screen (screen-view-only quality, 72 dpi images)

-dPDFSETTINGS=/ebook (low quality, 150 dpi images)

-dPDFSETTINGS=/printer (high quality, 300 dpi images)

-dPDFSETTINGS=/prepress (high quality, color preserving, 300 dpi imgs)

-dPDFSETTINGS=/default (almost identical to /screen)