Multipage PDF watermarking

[miragium]

Hello IM people,

I'm on linux and I want to put together a command that can take a pdf from the standard input, watermark it, and write it on the standard output. I turned to ImageMagick because of all the features and also because the rasterisation of pdfs was perfect for my use case.

After skimming this forum and some other ressources, I managed to put together this command :

Code: Select all

convert pdf:- -write mpr:base \
\( mask.png -shade 30x30 -blur 0x1 +level 45%,55% -write mpr:water +delete \) \ # create the watermark logo from a black and white image
\( +clone -tile mpr:water -draw "color 0,0 reset" -write mpr:tile +delete \) \ # tile it to the input image
+delete \
mpr:tile mpr:base \ # the order is important here, so that the compose effect can work the way I want
-compose Overlay -composite \
pdf:-

This does what I want, but only work for single page document. I can't find how to make it treat all the pages of a document. I know about the use of bracket to select pages, but I don't know how to apply it here.

Is it possible to do this with ImageMagick (I'm using 6.8, but could deploy 7 if necessary), or should I just split and merge the pdfs with something like pdftk ?

The latter solution would be suboptimal for me, as this would mean I would need to create temporary files, and because the pdfs are coming from and going to another machine through a http service, this would slow down the process.

[snibgo]

"-composite" works with two input files: a destination and a source.

You want multiple destinations and a single source, or single destination and multiple sources. "-layers composite" does that. It needs a "null:" image between the destination(s) and source(s). See http://www.imagemagick.org/script/comma ... php#layers

The command could be something like this (untested):

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convert pdf:- -write mpr:base -delete 0--1 \
 \( mask.png -shade 30x30 -blur 0x1 +level 45%,55% -write mpr:water +delete \) \ # create the watermark logo from a black and white image 
\( +clone -tile mpr:water -draw "color 0,0 reset" -write mpr:tile +delete \) \ # tile it to the input image 
+delete \
 mpr:tile mull: mpr:base \ # the order is important here, so that the compose effect can work the way I want 
-compose Overlay -layers composite \
 pdf:-

[miragium]

Thanks. This was not enough to do it, but put me on the right track, and I think I'm starting to grasp how this all work.

To correctly handle multiple pages, I also had to change some of the other delete and the clone like you did with the first delete, to correctly manipulated all pages.

Here is the final command :

Code: Select all

convert pdf:- -write mpr:base \
\( mask.png -shade 30x30 -blur 0x1 +level 45%,55% -write mpr:water +delete \) \
\( -clone 0--1 -tile mpr:water -draw "color 0,0 reset" -write mpr:tile -delete 0--1 \) \
-delete 0--1 \
mpr:tile null: mpr:base \
-compose Overlay -layers composite \
pdf:-

I'm wondering if I could make it faster (the pdfs are sometime very large), but at least it's working.

If anyone has tips I'm listening, but anyway my main issue is resolved. Thanks again.

[snibgo]

Are all the PDF pages the same size? Your mpr:tile will contain one image per page. If the pages are the same size, then all the mpr:tile images will be identical, so effort has been duplicated. You can reduce this duplication by cloning just one page.

[miragium]

Sometimes not, so I will leave it like this.

I tried to avoid the unnecessary writes and deletes, but it didn't made any noticeable difference.

Also, will doing that, I noticed that the Overlay effect that I'm using doesn't have the same result between version 6 and 7. Is that normal ? Should I open an new topic about this ? If this is normal, where can I find updated explanation of the different compose algorithm (I'm currently using this ressource which use v6.6 apparently, and I find the dest / src grayscale graphs very useful).

[snibgo]

Cloning, and writing to "mpr:", create new image structures with a pointer to the original pixels so don't actually copy pixels, so they are fast.

"-compose overlay" should have the same effect between v6 and v7. If they don't, please post a simple example in bugs, with the exact command, and input and output images.