Save RGB image as PPM format - c++

Question

I am trying to create RGB image in C++. I am not using any image libraries like OpenCv.
Firstly, I tried to create grayscale image. I want to draw rectangle to image. I am giving parameters at function like starting points, width, height etc. This code lines are working good for this grayscale challenge but I am trying to increase color channels to 3 like RGB. Then, I am setting Red, Green and Blue values but it is not working. This is my problem.
How can I work correctly?
x => starting point where x coordinate
y => starting point where y coordinate
width => rectangle width
height => rectangle height
value => RGB or Grayscale color value
My codes
Image::Image(int width, int height, int n_channels, int step)
{
cout << "Image constructor is running!" << endl;
m_width = width;
m_height = height;
m_n_channels = n_channels;
m_step = m_width*m_n_channels;
if (m_step < step)
m_step = step;
m_data = new uchar[m_step*height];
}
Image* Image::new_gray(int width, int height)
{
cout << "New gray image is creating!" << endl;
return new Image(width, height, 1);
}
Image* Image::new_rgb(int width, int height)
{
cout << "New RGB image is creating!" << endl;
return new Image(width, height, 3);
}
void Image::set_rect(int x, int y, int width, int height, uchar value)
{
if (x < 0) {
width += x;
x = 0;
}
if (y < 0) {
height += y;
y = 0;
}
for (int j = y; j < y+height; ++j) {
if (j >= m_height)
break;
uchar* row_data = data(j);
for (int i = x; i < x+width; ++i) {
if (i >= m_width)
break;
for (int c = 0; c < m_n_channels; ++c)
if (c == 0) {
row_data[i*m_n_channels + c] = value;
} else if (c == 1) {
row_data[i*m_n_channels + c] = value;
} else if (c == 2) {
row_data[i*m_n_channels + c] = value;
}
}
}
}
bool Image::write_pnm(const std::string& filename) const
{
if (m_n_channels != 1) {
const string magic_head = "P6";
ofstream fout;
string extended_name = filename + ".ppm";
fout.open(extended_name.c_str(), ios::out | ios::binary);
fout << magic_head << "\n";
fout << m_width << " " << m_height << " 255\n";
for (int y = 0; y < m_height; ++y) {
const uchar *row_data = data(y);
cout << reinterpret_cast<const char*>(row_data);
fout.write(reinterpret_cast<const char*>(row_data), m_width*sizeof(uchar));
}
fout.close();
return true;
}
const string magic_head = "P5";
ofstream fout;
string extended_name = filename + ".pgm";
fout.open(extended_name.c_str(), ios::out | ios::binary);
fout << magic_head << "\n";
fout << m_width << " " << m_height << " 255\n";
for (int y = 0; y < m_height; ++y) {
const uchar *row_data = data(y);
fout.write(reinterpret_cast<const char*>(row_data), m_width*sizeof(uchar));
}
fout.close();
return true;
}
My main function
#include <cstdlib>
#include <iostream>
#include "image.h"
using std::cout;
using std::endl;
using ceng391::Image;
int main(int argc, char** argv)
{
Image* gray = Image::new_gray(128, 128);
cout << "(" << gray->w() << "x" << gray->h() << ") channels: "
<< gray->n_ch() << " step: " << gray->step() << endl;
gray->set_zero();
gray->set_rect(32, 32, 64, 64, 255);
gray->write_pnm("/tmp/test_image");
Image* rgb_image = Image::new_rgb(128,128);
cout << "(" << rgb_image->w() << "x" << rgb_image->h() << ") channels: "
<< rgb_image->n_ch() << " step: " << rgb_image->step() << endl;
rgb_image->set_zero_rgb();
rgb_image->set_rect(32, 32, 64, 64, 150);
rgb_image->write_pnm("/tmp/test_image_rgb");
delete gray;
delete rgb_image;
return EXIT_SUCCESS;
}

Answer 1

This code is working for grayscale images because grayscale images have same number of pixels with width.
fout.write(reinterpret_cast<const char*>(row_data), m_width*sizeof(uchar));
But when I wanted to save RGB images, increased number of pixels 3 times. One pixel respresents via 3 channels so need to multiply stream size with 3 (R,G,B channels) for one pixel.
fout.write(reinterpret_cast<const char*>(row_data), m_width*sizeof(uchar)*3);