CODEWITHSUNDEEP
pdfimagemagickgraphicsmagick
Hayden
Hayden

Reputation: 163

Converting ImageMagick command to GraphicsMagick

In order to increase speed of a conversion, and avoid bugs, I'd like to convert the following ImageMagick command to a GraphicsMagick command.

This upcasts a PDF of any size to 300 DPI, then converts that PDF to a high quality 8.5x11 PDF in ImageMagick.

convert -density 300 ~/Desktop/10x11.pdf -density 300 -resize 2550x3300 -gravity center -extent 2550x3300 -colorspace Gray ~/Desktop/8.5x11.pdf

Running the same command in GraphicsMagick yields a PDF that is 35x45 inches. This is because the interpreted density of the final PDF is 72 (rather than 300) for some reason. 

gm convert -density 300 ~/Desktop/10x11.pdf -density 300 -resize 2550x3300 -gravity center -extent 2550x3300 -colorspace Gray ~/Desktop/35x45.pdf

The following yields a (blurry) 8.5x11inch PDF.

gm convert -density 300 ~/Desktop/10x11.pdf -density 300 -resize 612x792 -gravity center -extent 612x792 -colorspace Gray ~/Desktop/8.5x11.pdf

Any ideas on what I am doing wrong here? The aim to generate crisp 8.5x11 inch PDFs using GraphicsMagick.

Upvotes: 0

Views: 967

Answers (1)

jcupitt
jcupitt

Reputation: 11220

I realize you asked for a graphicsmagick solution, but if you're open to other libraries, libvips is usually faster at tasks like this.

Imagemagick and Graphicsmagick use Ghostscript for PDF rendering. libvips uses poppler instead: this library can generate high-quality anti-aliased bitmaps from PDFs at any size. You don't need to render at high resolution and then downsize.

On this laptop, I see:

$ /usr/bin/time -f %M:%e convert -density 300 ISO_12233-reschart.pdf -density 300 -resize 2550x3300 -gravity center -extent 2550x3300 -colorspace Gray x.pdf
250460:2.51

So 250MB of memory and 2.5s to generate your PDF.

The libvips equivalent would be:

#!/bin/bash

vips thumbnail $1 t1.v 2550 --height 3300 
vips colourspace t1.v t2.v b-w
# drop any alpha channels
if [ $(vipsheader -f bands t2.v) -gt 1 ]; then
        vips extract_band t2.v t3.v 0
        mv t3.v t2.v
fi
vips gravity t2.v t3.v centre 2550 3300 --extend white
vips magicksave t3.v $2

I see:

$ /usr/bin/time -f %M:%e ./process.sh ISO_12233-reschart.pdf x.pdf
110168:1.05

110MB of memory and 1.05s.

Are you sure you need PDF output? The PDFs you are generating are not "real" PDFs, they are bitmaps with a PDF wrapper. I would use PNG instead:

#!/bin/bash

vips thumbnail $1 t1.v 2550 --height 3300 
vips colourspace t1.v t2.v b-w
# drop any alpha channels
if [ $(vipsheader -f bands t2.v) -gt 1 ]; then
        vips extract_band t2.v t3.v 0
        mv t3.v t2.v
fi
vips gravity t2.v $2 centre 2550 3300 --extend white

I now see:

$ /usr/bin/time -f %M:%e ./process.sh ~/pics/ISO_12233-reschart.pdf x.png
58324:0.59

60MB of memory and 0.6s.

If you're able to use something like Python instead of bash, you can get it a bit quicker still.

#!/usr/bin/python3

import sys
import pyvips

x = pyvips.Image.thumbnail(sys.argv[1], 2550, height=3300)
x = x.colourspace("b-w")
if x.bands > 1:
    x = x.extract_band(0)
x = x.gravity("centre", 2550, 3300, extend="white")
x.write_to_file(sys.argv[2])

Now 0.5s because there are no temporary files.

Upvotes: 2

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