Gimp layer and pdf


I am using gimp to mask batches of pdf technical drawings.
The way I work is I import several pdf drawings as layers. Then I make a transparent layer with black boxes on it so some parts of the pdf is masked.
I print the drawing as a pdf so the pdf has the black boxes and are invisible. Unfortunately the file size of the new pdf is crazy. For example the original pdf is 80kb, the same pdf masked in gimp and saved as pdf is 600kb.

Is there any way to solve this problem, because I need to email these files.

Many thanks

If I need to place it in another topic/forum then please let me know.

Bennie from Holland

If these are technical drawings, I would guess that they are vector graphics. GIMP converts them to a raster format. PDF (and PS) can contain vector and raster information. If you combine several PDFs into a single one, converting it to a raster format and then export it as a PDF (containing raster data), this will tend to increase the size, possibly by a large amount.

There are various ways of dealing with this problem, depending on circumstances. One way would be to export the file as a JPEG instead. In the menu for exporting JPEGs, there is a slider which allows you to reduce the quality. I believe this largely affects the number of colors represented. Technical drawings don’t usually contain very many colors, so it shouldn’t make much difference. I’ve had good results reducing the quality by 25% to 50%, depending on the graphics. You could try converting the JPEGs to PDF afterwards. I wouldn’t expect a huge increase in file size, but you’d have to test this.

600K isn’t much these days.

Your problem is that being a bitmap/raster editor Gimp converts the vector graphics in the PDF to raster which is somewhat bulky (the output PDF becomes merely a container for JPEG images)… A vector graphics editor would create a much smaller output PDF, with actual vector graphics
Note that for your specific purpose the raster output may be better: it you add a mask in a vector editor it covers an existing object but that object is still in the exported file, and a knowledgeable person could unmask it. With a raster image what has been covered is irrecoverable.

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