May 08

Quickly: How to render a PDF to an image in C++?

Using Poppler, of course!
Poppler is a very useful tool for handling PDF, so I've discovered lately. Having tried both muPDF and ImageMagick's Magick++ and failed, Poppler stepped up to the challenge and paid off.

So here's a small example of how work the API (with OpenCV, naturally):

#include <iostream>
#include <fstream>
#include <sstream>
#include <opencv2/opencv.hpp>
#include <poppler-document.h>
#include <poppler-page.h>
#include <poppler-page-renderer.h>
#include <poppler-image.h>

using namespace cv;
using namespace std;
using namespace poppler;

Mat readPDFtoCV(const string& filename,int DPI) {
    document* mypdf = document::load_from_file(filename);
    if(mypdf == NULL) {
        cerr << "couldn't read pdf\n";
        return Mat();
    cout << "pdf has " << mypdf->pages() << " pages\n";
    page* mypage = mypdf->create_page(0);

    page_renderer renderer;
    image myimage = renderer.render_page(mypage,DPI,DPI);
    cout << "created image of  " << myimage.width() << "x"<< myimage.height() << "\n";

    Mat cvimg;
    if(myimage.format() == image::format_rgb24) {
    } else if(myimage.format() == image::format_argb32) {
    } else {
        cerr << "PDF format no good\n";
        return Mat();
    return cvimg;

All you have to do is give it the DPI (say you want to render in 100 DPI) and a filename.
Keep in mind it only renders the first page, but getting the other pages is just as easy.

That's it, enjoy!