Concatenating PDF files in Linux
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Every so often I need to combine several images into a single PDF. First, to convert an image to a PDF we can use imagemagick.
convert -quality 100 Image.png Scanned.pdf
To combine or concatenate multiple PDF files, we can use ghostscript.
gs -sDEVICE=pdfwrite \
-sOUTPUTFILE=output.pdf \
-dNOPAUSE \
-dBATCH \
input0.pdf input1.pdf input2.pdf
| Flag | Description |
|---|---|
-sDEVICE |
Device used for processing the output file type. Use pdfwrite to write to a PDF file. |
-sOUTPUTFILE |
Path to save the resulting file output. |
-dNOPAUSE |
Disables the prompting and pausing at the end of each page. |
-dBATCH |
Finishes interpreting after processing the inputted files |
Alternatively you can use pdftk
pdftk input0.pdf input1.pdf input2.pdf \
cat output output.pdf
Lastly, you can also use imagemagick. Do note, however, that this program often leads to larger file sizes.
convert input0.pdf input1.pdf input2.pdf output.pdf
Aside: Pixel Densities
One issue I came across is that the pages were of different sizes. This is often because the pages can be of different pixel densities.
To check run pdfimages and look at the 3rd to last and 2nd to last columns:
pdfimages -list filename.pdf
page num type width height color comp bpc enc interp object ID x-ppi y-ppi size ratio
--------------------------------------------------------------------------------------------
1 0 image 613 77 rgb 3 8 jpeg no 8 0 1071 1076 9456B 6.7%
1 1 image 2692 3496 rgb 3 8 jpeg no 9 0 329 329 418K 1.5%
2 2 image 613 77 rgb 3 8 jpeg no 8 0 915 919 9456B 6.7%
2 3 image 2300 3016 rgb 3 8 jpeg no 15 0 282 282 322K 1.6%
3 4 image 613 77 rgb 3 8 jpeg no 8 0 937 942 9456B 6.7%
3 5 image 2356 3024 rgb 3 8 jpeg no 21 0 288 288 150K 0.7%
4 6 image 1686 2200 rgb 3 8 jpeg no 27 0 204 204 622K 5.7%
5 7 image 5100 7016 rgb 3 8 jpeg no 33 0 600 600 1193K 1.1%
6 8 image 613 77 rgb 3 8 jpeg no 8 0 1104 1110 9456B 6.7%
6 9 image 2776 3720 rgb 3 8 jpeg no 38 0 339 339 231K 0.8%
7 10 image 613 77 rgb 3 8 jpeg no 8 0 939 943 9456B 6.7%
7 11 image 2360 3072 rgb 3 8 jpeg no 44 0 289 289 151K 0.7%
We can then use imagemagick to enforce a certain pixel density. The tradeoff being that the file size might increase.
convert -density 300 input.pdf output.pdf
If you happen to know a different way to enforce a pixel density that doesn’t have a file size increase tradeoff. Please get in touch.