Using Boost.GIL to convert an image into “raw” bytes

Question

Goal

I\'m trying to move towards Boost GIL to replace some similar functionality I\'ve implemented that is reaching the end of its maintainable life.

I have

Answer 1

A complete, simplified form of the actual code I ended up using is:

#include 
#include 
#include 
#include 
#include 

struct dimension {
  int w,h;
};

namespace {
struct PixelInserter {
    std::vector* storage;
    PixelInserter(std::vector* s) : storage(s) {}
    void operator()(boost::gil::rgb8_pixel_t p) const {
        using boost::gil::at_c;
        storage->push_back(at_c<0>(p));
        storage->push_back(at_c<1>(p));
        storage->push_back(at_c<2>(p));
    }
};

// This could probably share code with the PixelInserter
struct PixelWriter {
    const uint8_t *pixels;
    PixelWriter(const uint8_t *pixels) : pixels(pixels) {}
    void operator()(boost::gil::rgb8_pixel_t& p) {
        using boost::gil::at_c;
        at_c<0>(p) = *pixels++;
        at_c<1>(p) = *pixels++;
        at_c<2>(p) = *pixels++;
    }
};
}

void savePNG(const std::string& filename, const uint8_t *pixels, const dimension& d) {
    boost::gil::rgb8_image_t img(d.w, d.h);
    for_each_pixel(view(img), PixelWriter(pixels));
    boost::gil::png_write_view(filename, view(img));
}

std::vector readPNG(const std::string& fn, dimension& d) {
    boost::gil::rgb8_image_t image_type;
    image_type img;
    png_read_image(fn, img);
    d.w = img.width();
    d.h = img.height();

    std::vector storage;
    storage.reserve(d.w*d.h*boost::gil::num_channels());
    for_each_pixel(const_view(img), PixelInserter(&storage));
    return storage;
}

int main(int argc, char **argv) {
  dimension d;
  const std::vector pixels = readPNG(argv[1], d);
  savePNG(argv[2], &pixels[0], d);
}

I originally had the following before I included any of the GIL headers:

#define png_infopp_NULL (png_infopp)NULL
#define int_p_NULL (int*)NULL

I'm not sure exactly what issue they fixed with the version of boost I had at the time, but they don't seem to be required with 1.48.