Read/Write to PPM Image File C++
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;
};
user4640007
Updated on November 23, 2020Comments
-
user4640007 over 3 years
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, PPMObject &other) { inputStream.seekg(0, ios::end); int size = inputStream.tellg(); inputStream.seekg(0, ios::beg); other.m_Ptr = new char[size]; while (inputStream >> other.m_Ptr >> other.width >> other.height >> other.maxColVal) { other.magicNum = (string) other.m_Ptr; } return inputStream; }
My values correspond to the actual file. So I cheerfully attempt to write the data:
std::ostream& operator <<(std::ostream &outputStream, const PPMObject &other) { outputStream << "P6" << " " << other.width << " " << other.height << " " << other.maxColVal << " " ; outputStream << other.m_Ptr; return outputStream; }
I am making sure to open the file using std::ios::binary for both reading and writing:
int main () { PPMObject ppmObject = PPMObject(); std::ifstream image; std::ofstream outFile; image.open("C:\\Desktop\\PPMImage.ppm", std::ios::binary); image >> ppmObject; image.clear(); image.close(); outFile.open("C:\\Desktop\\NewImage.ppm", std::ios::binary); outFile << ppmObject; outFile.clear(); outFile.close(); return 0; }
Logic Error:
I am only writing a portion of the image. There is no problem with the header or opening the file manually.
Class public member variables:
The m_Ptr member variable is a char * and height, width maxColrVal are all integers.
Attempted Solution:
Using inputStream.read and outputStream.write to read and write data but I don't know how and what I have tried doesn't work.
Since my char * m_Ptr contains all of the pixel data. I can iterate through it:
for (int I = 0; I < other.width * other.height; I++) outputStream << other.m_Ptr[I];
But this causes a run-time error for some reason..