example_png2bmp.cpp

/*
LodePNG Examples

Copyright (c) 2005-2012 Lode Vandevenne

This software is provided 'as-is', without any express or implied
warranty. In no event will the authors be held liable for any damages
arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:

    1. The origin of this software must not be misrepresented; you must not
    claim that you wrote the original software. If you use this software
    in a product, an acknowledgment in the product documentation would be
    appreciated but is not required.

    2. Altered source versions must be plainly marked as such, and must not be
    misrepresented as being the original software.

    3. This notice may not be removed or altered from any source
    distribution.
*/

#include "lodepng.h"
#include <iostream>

/*
This example converts a PNG file to a BMP file.
NOTE: it overwrites the output file without warning if it exists!
Give the PNG and the BMP file names as command line arguments.
*/

/*
g++ lodepng.cpp example_png2bmp.cpp -Wall -Wextra -pedantic -ansi -lSDL -O3
*/



//Input image must be RGB buffer (3 bytes per pixel), but you can easily make it
//support RGBA input and output by changing the inputChannels and/or outputChannels
//in the function to 4.
void encodeBMP(std::vector<unsigned char>& bmp, const unsigned char* image, int w, int h) {
  //3 bytes per pixel used for both input and output.
  int inputChannels = 3;
  int outputChannels = 3;

  //bytes 0-13
  bmp.push_back('B'); bmp.push_back('M'); //0: bfType
  bmp.push_back(0); bmp.push_back(0); bmp.push_back(0); bmp.push_back(0); //2: bfSize; size not yet known for now, filled in later.
  bmp.push_back(0); bmp.push_back(0); //6: bfReserved1
  bmp.push_back(0); bmp.push_back(0); //8: bfReserved2
  bmp.push_back(54 % 256); bmp.push_back(54 / 256); bmp.push_back(0); bmp.push_back(0); //10: bfOffBits (54 header bytes)

  //bytes 14-53
  bmp.push_back(40); bmp.push_back(0); bmp.push_back(0); bmp.push_back(0);  //14: biSize
  bmp.push_back(w % 256); bmp.push_back(w / 256); bmp.push_back(0); bmp.push_back(0); //18: biWidth
  bmp.push_back(h % 256); bmp.push_back(h / 256); bmp.push_back(0); bmp.push_back(0); //22: biHeight
  bmp.push_back(1); bmp.push_back(0); //26: biPlanes
  bmp.push_back(outputChannels * 8); bmp.push_back(0); //28: biBitCount
  bmp.push_back(0); bmp.push_back(0); bmp.push_back(0); bmp.push_back(0);  //30: biCompression
  bmp.push_back(0); bmp.push_back(0); bmp.push_back(0); bmp.push_back(0);  //34: biSizeImage
  bmp.push_back(0); bmp.push_back(0); bmp.push_back(0); bmp.push_back(0);  //38: biXPelsPerMeter
  bmp.push_back(0); bmp.push_back(0); bmp.push_back(0); bmp.push_back(0);  //42: biYPelsPerMeter
  bmp.push_back(0); bmp.push_back(0); bmp.push_back(0); bmp.push_back(0);  //46: biClrUsed
  bmp.push_back(0); bmp.push_back(0); bmp.push_back(0); bmp.push_back(0);  //50: biClrImportant

  /*
  Convert the input RGBRGBRGB pixel buffer to the BMP pixel buffer format. There are 3 differences with the input buffer:
  -BMP stores the rows inversed, from bottom to top
  -BMP stores the color channels in BGR instead of RGB order
  -BMP requires each row to have a multiple of 4 bytes, so sometimes padding bytes are added between rows
  */

  int imagerowbytes = outputChannels * w;
  imagerowbytes = imagerowbytes % 4 == 0 ? imagerowbytes : imagerowbytes + (4 - imagerowbytes % 4); //must be multiple of 4

  for(int y = h - 1; y >= 0; y--) { //the rows are stored inversed in bmp
    int c = 0;
    for(int x = 0; x < imagerowbytes; x++) {
      if(x < w * outputChannels) {
        int inc = c;
        //Convert RGB(A) into BGR(A)
        if(c == 0) inc = 2;
        else if(c == 2) inc = 0;
        bmp.push_back(image[inputChannels * (w * y + x / outputChannels) + inc]);
      }
      else bmp.push_back(0);
      c++;
      if(c >= outputChannels) c = 0;
    }
  }

  // Fill in the size
  bmp[2] = bmp.size() % 256;
  bmp[3] = (bmp.size() / 256) % 256;
  bmp[4] = (bmp.size() / 65536) % 256;
  bmp[5] = bmp.size() / 16777216;
}

int main(int argc, char *argv[]) {
  if(argc < 3) {
    std::cout << "Please provide input PNG and output BMP file names" << std::endl;
    return 0;
  }
  const char* infile = argv[1];
  const char* outfile = argv[2];


  std::vector<unsigned char> image; //the raw pixels
  unsigned width, height;

  unsigned error = lodepng::decode(image, width, height, infile, LCT_RGB, 8);

  if(error) {
    std::cout << "error " << error << ": " << lodepng_error_text(error) << std::endl;
    return 0;
  }

  std::vector<unsigned char> bmp;
  encodeBMP(bmp, &image[0], width, height);

  lodepng::save_file(bmp, outfile);
}