// load png image with freeimage.

#include <stdio.h>
#include <iostream>
#include <FreeImage.h>

const char *outfile = "out.png";

int main(int argc, char *argv[])
{
  if (argc != 2)
  {
    printf("Usage:\n\t01_load_png01.exe IN.png\n");
    return -1;
  }

  FreeImage_Initialise(FALSE);

  printf("FreeImage ver. %s\n", FreeImage_GetVersion());
  printf("%s\n\n", FreeImage_GetCopyrightMessage());

  try
  {
    auto filename = argv[1];

    // get input image format
    FREE_IMAGE_FORMAT fif = FIF_UNKNOWN;
    int flag = 0;

    fif = FreeImage_GetFileType(filename);
    if (fif == FIF_UNKNOWN)
      fif = FreeImage_GetFIFFromFilename(filename);

    if (fif == FIF_PNG)
      flag = PNG_DEFAULT;
    else if (fif == FIF_BMP)
      flag = BMP_DEFAULT;
    else if (fif == FIF_GIF)
      flag = GIF_DEFAULT;
    else if (fif == FIF_JPEG)
      flag = JPEG_DEFAULT;

    // load image
    FIBITMAP *image = FreeImage_Load(fif, filename, flag);
    if (image)
      printf("Load : %s\n", filename);
    else
      throw std::runtime_error("Load failed");

    // convert to 24bit image
    FIBITMAP *image24 = FreeImage_ConvertTo24Bits(image);

    // convert greyscale
    int width = FreeImage_GetWidth(image24);
    int height = FreeImage_GetHeight(image24);
    FIBITMAP *newimg = FreeImage_Allocate(width, height, 24);
    RGBQUAD col;

    for (int y = 0; y < height; y++)
    {
      for (int x = 0; x < width; x++)
      {
        FreeImage_GetPixelColor(image24, x, y, &col);

        double ncol = 0.299 * col.rgbRed + 0.587 * col.rgbGreen + 0.114 * col.rgbBlue;
        if (ncol < 0)
          ncol = 0;
        if (ncol > 255)
          ncol = 255;
        col.rgbRed = int(ncol);
        col.rgbGreen = int(ncol);
        col.rgbBlue = int(ncol);
        
        FreeImage_SetPixelColor(newimg, x, y, &col);
      }
    }

    // save png image
    if (FreeImage_Save(FIF_PNG, newimg, outfile, PNG_DEFAULT))
      printf("Save : %s\n", outfile);
    else
      throw std::runtime_error("Save failed");

    FreeImage_Unload(image);
    FreeImage_Unload(newimg);
  }
  catch (std::exception &e)
  {
    std::cout << "exception!\n"
              << e.what() << std::endl;
  }

  FreeImage_DeInitialise();

  return 0;
}