Read/Write to PPM Image File C++

Question

Trying to read and write to/from a PPM Image file (.ppm) in the only way I know how:

std::istream& operator >>(std::istream &inputStream, PPMOb         


        

Answer 1

Based on http://fr.wikipedia.org/wiki/Portable_pixmap, P6 is a binary image. This reads a single image. Note that no checking is performed. This needs to be added.

std::istream& operator >>(std::istream &inputStream, PPMObject &other)
{
    inputStream >> other.magicNum;
    inputStream >> other.width >> other.height >> other.maxColVal;
    inputStream.get(); // skip the trailing white space
    size_t size = other.width * other.height * 3;
    other.m_Ptr = new char[size];
    inputStream.read(other.m_Ptr, size);
    return inputStream;
}

This code writes a single image.

std::ostream& operator <<(std::ostream &outputStream, const PPMObject &other)
{
    outputStream << "P6"     << "\n"
        << other.width       << " "
        << other.height      << "\n"
        << other.maxColVal   << "\n"
       ;
    size_t size = other.width * other.height * 3;
    outputStream.write(other.m_Ptr, size);
    return outputStream;
}

m_Ptr contains only the RGB pixel values.

I tested the code on an image I downloaded from the web (http://igm.univ-mlv.fr/~incerti/IMAGES/COLOR/Aerial.512.ppm) and using the following structure PPMObject it worked.

struct PPMObject
{
  std::string magicNum;
  int width, height, maxColVal;
  char * m_Ptr;
};