convert video into ppm files

Question

I have found a tutorial to convert a video into ppm. http://webcache.googleusercontent.com/search?q=cache:http://dranger.com/ffmpeg/tutorial01.html&gws_rd=cr&ei=BU9tWNyFNsvCjwTXqbuwDg

However, I don't get why width*3 here.

void SaveFrame(AVFrame *pFrame, int width, int height, int iFrame) {
  FILE *pFile;
  char szFilename[32];
  int  y;

  // Open file
  sprintf(szFilename, "frame%d.ppm", iFrame);
  pFile=fopen(szFilename, "wb");
  if(pFile==NULL)
    return;

  // Write header
  fprintf(pFile, "P6\n%d %d\n255\n", width, height);

  // Write pixel data
  for(y=0; y<height; y++) {

    fwrite(pFrame->data[0]+y*pFrame->linesize[0], 1, width*3, pFile);
  }

  // Close file
  fclose(pFile);
}

Answer 1

Probably because for every image point you have three channels (RGB).