CODEWITHSUNDEEP
ruby-on-railsrubyimagepdfpdf-generation
letronje
letronje

Reputation: 9148

Finding coordinates of an image in a pdf to replace it with another one

I have a pdf which I would like to use as a template to create a new pdf. The goal is to place an image inside a particular placeholder rectangle in the original pdf. The creation of the original pdf is under my control but the placeholder rectangle/bounds might be anywhere in the pdf. I am thinking of using a dummy image(of same dimensions) as the placeholder rectangle in the original pdf.

The Prawn gem supports placing an image at a given absolute/relative position within a page.

The trouble is that since the rectangle or dummy-image could be anywhere in the original pdf, I don't know what values to use for the following

pdf.image "/path/to/image", :at => [x,y] prawn call

Is there a way to get the coordinates of an image in the original pdf. My primitive understanding tells me that one would have to render the entire pdf to know this. Is that right ? If yes, what would be a good way to render pdf in memory (headless) and get the co-ordinates of various pdf objects(like bounding rectangles, images, etc).

I am not limited by language/runtime here as long as I can trigger it programmatically.

What could be other approaches to this problem ?

Upvotes: 0

Views: 568

Answers (1)

user2846289
user2846289

Reputation: 2215

Not an answer (e.g. I don't know the Ruby language), but in lieu of any others, and because I can't post a comment yet, here's what I think.

If conditions stated above are true (placeholder and replacement images are exactly same size + same color model e.g. RGB 24 bps) and you control template creation (therefore you can store placeholder inside PDF uncompressed), it can be as quick and dirty as raw replacement in a file treated as byte string. E.g. placeholder filled with red, then you search for pattern (0xFF0000) x W*H and replace it with raw image data. Which, of course, you can get any way you like, e.g.:

convert my_image.jpg RGB:- | ...

If this solution is too dirty or conditions not exact, then parse page content stream for construct like

width 0 0 height x y cm
/name Do

It's not cleanest, either, but for vast number of simple page descriptions x and y are the coordinates you are looking for.

Further, if you control template creation, why don't you store additional information inside pdf as e.g. custom keys in Info dictionary, and then read them back when using the template.

Upvotes: 1

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