CPSC 120 Example of creating an image using nested for loops and GraphicsMagick.

cpsc120_image.cc

// Gist https://gist.github.com/mshafae/1e50f814b084f19af6a702ba8f1b9d6d
// Filename cpsc120_image.cc
// CompileCommand clang++ -std=c++17 -I /usr/include/GraphicsMagick -lGraphicsMagick++ cpsc120_image.cc
// Create a simple, small image from a given
// filename. GraphicsMagick will figure out how to output to the given file
// format.
// Supported formats: http://www.graphicsmagick.org/formats.html
// Example:
// clang++ -std=c++17 -I /usr/include/GraphicsMagick -lGraphicsMagick++
// cpsc120_image.cc
// ./a.out my_image.jpg
// ./a.out my_image.png

#include <Magick++.h>

#include <cmath>
#include <iostream>
#include <sstream>
#include <string>
#include <vector>

int main(int argc, char* argv[]) {
  // Set these to whatever dimensions you want the output image to be.
  // Warning: don't make this too big or your program will take a long time
  // to execute.
  const int kImageWidth{512};
  const int kImageHeight{512};
  // This initializes the image library we are using.
  Magick::InitializeMagick(*argv);
  std::vector<std::string> args{argv, argv + argc};
  if (args.size() < 2) {
    std::cout << "Please provide a path to a file.\n";
    std::cout << "For example: " << args.at(0) << " my_image.jpg\n";
    return 1;
  }
  std::string output_file_name;
  output_file_name = args.at(1);

  // Colors are defined with three channels: Red, Green, Blue.
  // The value for each channel is a floating point number between 0 and 1.
  // Black is all 0 values and white is all 1 values.
  Magick::ColorRGB white(1, 1, 1);
  Magick::Image image(Magick::Geometry(kImageWidth, kImageHeight), white);

  // We have a white image that is kImageWidth x kImageHeight. Let's
  // change the pixels in the image to a different color.
  // For every row, go through each pixel from left to right.
  // Think of the upper left hand corner of the image as the origin.
  // The rows go up and down (like a y-axis) and the columns go
  // left and right (like an x-axis).
  for (int row = 0; row < image.rows(); row++) {
    for (int column = 0; column < image.columns(); column++) {
      // Let's make red go from 0 to 1, from left to right
      double red{double(column) / double(image.columns() - 1)};
      // Let's make the green stay 0.0
      double green{0.0};
      // Let's make the blue stay 0.0
      double blue{0.0};
      // If you want to see what the image looks one color at a time
      // just use one of the colors instead of all three.
      // Just red
      // Magick::ColorRGB color{red, 0, 0};
      // Just green
      // Magick::ColorRGB color{0, green, 0};
      // Just blue
      // Magick::ColorRGB color{0, 0, blue};
      // We create a new color given the values of red, green, and blue.
      Magick::ColorRGB color{red, green, blue};

      // We set the pixel to the color we just created. The pixel
      // is located at (column, row)
      image.pixelColor(column, row, color);
    }
  }

  image.write(output_file_name);

  return 0;
}