title: libpng error: Read Error
body: <p>I has some png image. I open it. Than i save it to file. And when i try to open saved image i have the problem. <strong>libpng error: Read Error</strong> on <code>png_read_rows</code></p>
  
  <p><strong>Here is the writing code:</strong></p>
  
  <pre><code>png_structp png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
  png_infop info_ptr = png_create_info_struct(png_ptr);
  //created png struct
  
  setjmp(png_jmpbuf(png_ptr))
  //signed
  png_init_io(png_ptr, file);
  
  png_set_IHDR(png_ptr, info_ptr, width, height, 8, PNG_COLOR_TYPE_RGBA, PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
  //set header
  unsigned char * buffer = (unsigned char*)malloc(4 *width * height);
  // created buffer
  unsigned char ** row_pointers = (unsigned char**) malloc(height * sizeof(unsigned char *)); // created rows pointers
  for (int i= 0; i&lt; height ; i++) {
      row_pointers[i] = buffer + i * 4 * width;
  }
  
  memset(buffer, 255, 4 * height * width); // fill buffer with white image for example.
  // **I mean that the same problem is even when i do not write the opened image, 
  //but just fill it with white**.
  
  png_write_image(png_ptr, row_pointers);
  //write data
  
  png_write_end(png_ptr, NULL);
  
  png_destroy_write_struct(&amp;png_ptr, (png_infopp)NULL);
  </code></pre>