    /* pngtrans.c - transforms the data in a row (used by both readers and writers)
     *
     * Last changed in libpng 1.6.2 [April 25, 2013]
     * Copyright (c) 1998-2013 Glenn Randers-Pehrson
     * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
     * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
     *
     * This code is released under the libpng license.
     * For conditions of distribution and use, see the disclaimer
     * and license in png.h
     */

    #include "pngpriv.h"

    #if defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED)

    #if defined(PNG_READ_BGR_SUPPORTED) || defined(PNG_WRITE_BGR_SUPPORTED)
    /* Turn on BGR-to-RGB mapping */
    void PNGAPI
    png_set_bgr(png_structrp png_ptr)
    {
       png_debug(1, "in png_set_bgr");

       if (png_ptr == NULL)
          return;

       png_ptr->transformations |= PNG_BGR;
    }
    #endif

    #if defined(PNG_READ_SWAP_SUPPORTED) || defined(PNG_WRITE_SWAP_SUPPORTED)
    /* Turn on 16 bit byte swapping */
    void PNGAPI
    png_set_swap(png_structrp png_ptr)
    {
       png_debug(1, "in png_set_swap");

       if (png_ptr == NULL)
          return;

       if (png_ptr->bit_depth == 16)
          png_ptr->transformations |= PNG_SWAP_BYTES;
    }
    #endif

    #if defined(PNG_READ_PACK_SUPPORTED) || defined(PNG_WRITE_PACK_SUPPORTED)
    /* Turn on pixel packing */
    void PNGAPI
    png_set_packing(png_structrp png_ptr)
    {
       png_debug(1, "in png_set_packing");

       if (png_ptr == NULL)
          return;

       if (png_ptr->bit_depth < 8)
       {
          png_ptr->transformations |= PNG_PACK;
          png_ptr->usr_bit_depth = 8;
       }
    }
    #endif

    #if defined(PNG_READ_PACKSWAP_SUPPORTED)||defined(PNG_WRITE_PACKSWAP_SUPPORTED)
    /* Turn on packed pixel swapping */
    void PNGAPI
    png_set_packswap(png_structrp png_ptr)
    {
       png_debug(1, "in png_set_packswap");

       if (png_ptr == NULL)
          return;

       if (png_ptr->bit_depth < 8)
          png_ptr->transformations |= PNG_PACKSWAP;
    }
    #endif

    #if defined(PNG_READ_SHIFT_SUPPORTED) || defined(PNG_WRITE_SHIFT_SUPPORTED)
    void PNGAPI
    png_set_shift(png_structrp png_ptr, png_const_color_8p true_bits)
    {
       png_debug(1, "in png_set_shift");

       if (png_ptr == NULL)
          return;

       png_ptr->transformations |= PNG_SHIFT;
       png_ptr->shift = *true_bits;
    }
    #endif

    #if defined(PNG_READ_INTERLACING_SUPPORTED) || \
        defined(PNG_WRITE_INTERLACING_SUPPORTED)
    int PNGAPI
    png_set_interlace_handling(png_structrp png_ptr)
    {
       png_debug(1, "in png_set_interlace handling");

       if (png_ptr && png_ptr->interlaced)
       {
          png_ptr->transformations |= PNG_INTERLACE;
          return (7);
       }

       return (1);
    }
    #endif

    #if defined(PNG_READ_FILLER_SUPPORTED) || defined(PNG_WRITE_FILLER_SUPPORTED)
    /* Add a filler byte on read, or remove a filler or alpha byte on write.
     * The filler type has changed in v0.95 to allow future 2-byte fillers
     * for 48-bit input data, as well as to avoid problems with some compilers
     * that don't like bytes as parameters.
     */
    void PNGAPI
    png_set_filler(png_structrp png_ptr, png_uint_32 filler, int filler_loc)
    {
       png_debug(1, "in png_set_filler");

       if (png_ptr == NULL)
          return;

       /* In libpng 1.6 it is possible to determine whether this is a read or write
        * operation and therefore to do more checking here for a valid call.
        */
       if (png_ptr->mode & PNG_IS_READ_STRUCT)
       {
    #     ifdef PNG_READ_FILLER_SUPPORTED
             /* On read png_set_filler is always valid, regardless of the base PNG
              * format, because other transformations can give a format where the
              * filler code can execute (basically an 8 or 16-bit component RGB or G
              * format.)
              *
              * NOTE: usr_channels is not used by the read code!  (This has led to
              * confusion in the past.)  The filler is only used in the read code.
              */
             png_ptr->filler = (png_uint_16)filler;
    #     else
             png_app_error(png_ptr, "png_set_filler not supported on read");
             PNG_UNUSED(filler) /* not used in the write case */
             return;
    #     endif
       }

       else /* write */
       {
    #     ifdef PNG_WRITE_FILLER_SUPPORTED
             /* On write the usr_channels parameter must be set correctly at the
              * start to record the number of channels in the app-supplied data.
              */
             switch (png_ptr->color_type)
             {
                case PNG_COLOR_TYPE_RGB:
                   png_ptr->usr_channels = 4;
                   break;

                case PNG_COLOR_TYPE_GRAY:
                   if (png_ptr->bit_depth >= 8)
                   {
                      png_ptr->usr_channels = 2;
                      break;
                   }

                   else
                   {
                      /* There simply isn't any code in libpng to strip out bits
                       * from bytes when the components are less than a byte in
                       * size!
                       */
                      png_app_error(png_ptr,
                         "png_set_filler is invalid for low bit depth gray output");
                      return;
                   }

                default:
                   png_app_error(png_ptr,
                      "png_set_filler: inappropriate color type");
                   return;
             }
    #     else
             png_app_error(png_ptr, "png_set_filler not supported on write");
             return;
    #     endif
       }

       /* Here on success - libpng supports the operation, set the transformation
        * and the flag to say where the filler channel is.
        */
       png_ptr->transformations |= PNG_FILLER;

       if (filler_loc == PNG_FILLER_AFTER)
          png_ptr->flags |= PNG_FLAG_FILLER_AFTER;

       else
          png_ptr->flags &= ~PNG_FLAG_FILLER_AFTER;
    }

    /* Added to libpng-1.2.7 */
    void PNGAPI
    png_set_add_alpha(png_structrp png_ptr, png_uint_32 filler, int filler_loc)
    {
       png_debug(1, "in png_set_add_alpha");

       if (png_ptr == NULL)
          return;

       png_set_filler(png_ptr, filler, filler_loc);
       /* The above may fail to do anything. */
       if (png_ptr->transformations & PNG_FILLER)
          png_ptr->transformations |= PNG_ADD_ALPHA;
    }

    #endif

    #if defined(PNG_READ_SWAP_ALPHA_SUPPORTED) || \
        defined(PNG_WRITE_SWAP_ALPHA_SUPPORTED)
    void PNGAPI
    png_set_swap_alpha(png_structrp png_ptr)
    {
       png_debug(1, "in png_set_swap_alpha");

       if (png_ptr == NULL)
          return;

       png_ptr->transformations |= PNG_SWAP_ALPHA;
    }
    #endif

    #if defined(PNG_READ_INVERT_ALPHA_SUPPORTED) || \
        defined(PNG_WRITE_INVERT_ALPHA_SUPPORTED)
    void PNGAPI
    png_set_invert_alpha(png_structrp png_ptr)
    {
       png_debug(1, "in png_set_invert_alpha");

       if (png_ptr == NULL)
          return;

       png_ptr->transformations |= PNG_INVERT_ALPHA;
    }
    #endif

    #if defined(PNG_READ_INVERT_SUPPORTED) || defined(PNG_WRITE_INVERT_SUPPORTED)
    void PNGAPI
    png_set_invert_mono(png_structrp png_ptr)
    {
       png_debug(1, "in png_set_invert_mono");

       if (png_ptr == NULL)
          return;

       png_ptr->transformations |= PNG_INVERT_MONO;
    }

    /* Invert monochrome grayscale data */
    void /* PRIVATE */
    png_do_invert(png_row_infop row_info, png_bytep row)
    {
       png_debug(1, "in png_do_invert");

      /* This test removed from libpng version 1.0.13 and 1.2.0:
       *   if (row_info->bit_depth == 1 &&
       */
       if (row_info->color_type == PNG_COLOR_TYPE_GRAY)
       {
          png_bytep rp = row;
          png_size_t i;
          png_size_t istop = row_info->rowbytes;

          for (i = 0; i < istop; i++)
          {
             *rp = (png_byte)(~(*rp));
             rp++;
          }
       }

       else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA &&
          row_info->bit_depth == 8)
       {
          png_bytep rp = row;
          png_size_t i;
          png_size_t istop = row_info->rowbytes;

          for (i = 0; i < istop; i += 2)
          {
             *rp = (png_byte)(~(*rp));
             rp += 2;
          }
       }

    #ifdef PNG_16BIT_SUPPORTED
       else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA &&
          row_info->bit_depth == 16)
       {
          png_bytep rp = row;
          png_size_t i;
          png_size_t istop = row_info->rowbytes;

          for (i = 0; i < istop; i += 4)
          {
             *rp = (png_byte)(~(*rp));
             *(rp + 1) = (png_byte)(~(*(rp + 1)));
             rp += 4;
          }
       }
    #endif
    }
    #endif

    #ifdef PNG_16BIT_SUPPORTED
    #if defined(PNG_READ_SWAP_SUPPORTED) || defined(PNG_WRITE_SWAP_SUPPORTED)
    /* Swaps byte order on 16 bit depth images */
    void /* PRIVATE */
    png_do_swap(png_row_infop row_info, png_bytep row)
    {
       png_debug(1, "in png_do_swap");

       if (row_info->bit_depth == 16)
       {
          png_bytep rp = row;
          png_uint_32 i;
          png_uint_32 istop= row_info->width * row_info->channels;

          for (i = 0; i < istop; i++, rp += 2)
          {
             png_byte t = *rp;
             *rp = *(rp + 1);
             *(rp + 1) = t;
          }
       }
    }
    #endif
    #endif

    #if defined(PNG_READ_PACKSWAP_SUPPORTED)||defined(PNG_WRITE_PACKSWAP_SUPPORTED)
    static PNG_CONST png_byte onebppswaptable[256] = {
       0x00, 0x80, 0x40, 0xC0, 0x20, 0xA0, 0x60, 0xE0,
       0x10, 0x90, 0x50, 0xD0, 0x30, 0xB0, 0x70, 0xF0,
       0x08, 0x88, 0x48, 0xC8, 0x28, 0xA8, 0x68, 0xE8,
       0x18, 0x98, 0x58, 0xD8, 0x38, 0xB8, 0x78, 0xF8,
       0x04, 0x84, 0x44, 0xC4, 0x24, 0xA4, 0x64, 0xE4,
       0x14, 0x94, 0x54, 0xD4, 0x34, 0xB4, 0x74, 0xF4,
       0x0C, 0x8C, 0x4C, 0xCC, 0x2C, 0xAC, 0x6C, 0xEC,
       0x1C, 0x9C, 0x5C, 0xDC, 0x3C, 0xBC, 0x7C, 0xFC,
       0x02, 0x82, 0x42, 0xC2, 0x22, 0xA2, 0x62, 0xE2,
       0x12, 0x92, 0x52, 0xD2, 0x32, 0xB2, 0x72, 0xF2,
       0x0A, 0x8A, 0x4A, 0xCA, 0x2A, 0xAA, 0x6A, 0xEA,
       0x1A, 0x9A, 0x5A, 0xDA, 0x3A, 0xBA, 0x7A, 0xFA,
       0x06, 0x86, 0x46, 0xC6, 0x26, 0xA6, 0x66, 0xE6,
       0x16, 0x96, 0x56, 0xD6, 0x36, 0xB6, 0x76, 0xF6,
       0x0E, 0x8E, 0x4E, 0xCE, 0x2E, 0xAE, 0x6E, 0xEE,
       0x1E, 0x9E, 0x5E, 0xDE, 0x3E, 0xBE, 0x7E, 0xFE,
       0x01, 0x81, 0x41, 0xC1, 0x21, 0xA1, 0x61, 0xE1,
       0x11, 0x91, 0x51, 0xD1, 0x31, 0xB1, 0x71, 0xF1,
       0x09, 0x89, 0x49, 0xC9, 0x29, 0xA9, 0x69, 0xE9,
       0x19, 0x99, 0x59, 0xD9, 0x39, 0xB9, 0x79, 0xF9,
       0x05, 0x85, 0x45, 0xC5, 0x25, 0xA5, 0x65, 0xE5,
       0x15, 0x95, 0x55, 0xD5, 0x35, 0xB5, 0x75, 0xF5,
       0x0D, 0x8D, 0x4D, 0xCD, 0x2D, 0xAD, 0x6D, 0xED,
       0x1D, 0x9D, 0x5D, 0xDD, 0x3D, 0xBD, 0x7D, 0xFD,
       0x03, 0x83, 0x43, 0xC3, 0x23, 0xA3, 0x63, 0xE3,
       0x13, 0x93, 0x53, 0xD3, 0x33, 0xB3, 0x73, 0xF3,
       0x0B, 0x8B, 0x4B, 0xCB, 0x2B, 0xAB, 0x6B, 0xEB,
       0x1B, 0x9B, 0x5B, 0xDB, 0x3B, 0xBB, 0x7B, 0xFB,
       0x07, 0x87, 0x47, 0xC7, 0x27, 0xA7, 0x67, 0xE7,
       0x17, 0x97, 0x57, 0xD7, 0x37, 0xB7, 0x77, 0xF7,
       0x0F, 0x8F, 0x4F, 0xCF, 0x2F, 0xAF, 0x6F, 0xEF,
       0x1F, 0x9F, 0x5F, 0xDF, 0x3F, 0xBF, 0x7F, 0xFF
    };

    static PNG_CONST png_byte twobppswaptable[256] = {
       0x00, 0x40, 0x80, 0xC0, 0x10, 0x50, 0x90, 0xD0,
       0x20, 0x60, 0xA0, 0xE0, 0x30, 0x70, 0xB0, 0xF0,
       0x04, 0x44, 0x84, 0xC4, 0x14, 0x54, 0x94, 0xD4,
       0x24, 0x64, 0xA4, 0xE4, 0x34, 0x74, 0xB4, 0xF4,
       0x08, 0x48, 0x88, 0xC8, 0x18, 0x58, 0x98, 0xD8,
       0x28, 0x68, 0xA8, 0xE8, 0x38, 0x78, 0xB8, 0xF8,
       0x0C, 0x4C, 0x8C, 0xCC, 0x1C, 0x5C, 0x9C, 0xDC,
       0x2C, 0x6C, 0xAC, 0xEC, 0x3C, 0x7C, 0xBC, 0xFC,
       0x01, 0x41, 0x81, 0xC1, 0x11, 0x51, 0x91, 0xD1,
       0x21, 0x61, 0xA1, 0xE1, 0x31, 0x71, 0xB1, 0xF1,
       0x05, 0x45, 0x85, 0xC5, 0x15, 0x55, 0x95, 0xD5,
       0x25, 0x65, 0xA5, 0xE5, 0x35, 0x75, 0xB5, 0xF5,
       0x09, 0x49, 0x89, 0xC9, 0x19, 0x59, 0x99, 0xD9,
       0x29, 0x69, 0xA9, 0xE9, 0x39, 0x79, 0xB9, 0xF9,
       0x0D, 0x4D, 0x8D, 0xCD, 0x1D, 0x5D, 0x9D, 0xDD,
       0x2D, 0x6D, 0xAD, 0xED, 0x3D, 0x7D, 0xBD, 0xFD,
       0x02, 0x42, 0x82, 0xC2, 0x12, 0x52, 0x92, 0xD2,
       0x22, 0x62, 0xA2, 0xE2, 0x32, 0x72, 0xB2, 0xF2,
       0x06, 0x46, 0x86, 0xC6, 0x16, 0x56, 0x96, 0xD6,
       0x26, 0x66, 0xA6, 0xE6, 0x36, 0x76, 0xB6, 0xF6,
       0x0A, 0x4A, 0x8A, 0xCA, 0x1A, 0x5A, 0x9A, 0xDA,
       0x2A, 0x6A, 0xAA, 0xEA, 0x3A, 0x7A, 0xBA, 0xFA,
       0x0E, 0x4E, 0x8E, 0xCE, 0x1E, 0x5E, 0x9E, 0xDE,
       0x2E, 0x6E, 0xAE, 0xEE, 0x3E, 0x7E, 0xBE, 0xFE,
       0x03, 0x43, 0x83, 0xC3, 0x13, 0x53, 0x93, 0xD3,
       0x23, 0x63, 0xA3, 0xE3, 0x33, 0x73, 0xB3, 0xF3,
       0x07, 0x47, 0x87, 0xC7, 0x17, 0x57, 0x97, 0xD7,
       0x27, 0x67, 0xA7, 0xE7, 0x37, 0x77, 0xB7, 0xF7,
       0x0B, 0x4B, 0x8B, 0xCB, 0x1B, 0x5B, 0x9B, 0xDB,
       0x2B, 0x6B, 0xAB, 0xEB, 0x3B, 0x7B, 0xBB, 0xFB,
       0x0F, 0x4F, 0x8F, 0xCF, 0x1F, 0x5F, 0x9F, 0xDF,
       0x2F, 0x6F, 0xAF, 0xEF, 0x3F, 0x7F, 0xBF, 0xFF
    };

    static PNG_CONST png_byte fourbppswaptable[256] = {
       0x00, 0x10, 0x20, 0x30, 0x40, 0x50, 0x60, 0x70,
       0x80, 0x90, 0xA0, 0xB0, 0xC0, 0xD0, 0xE0, 0xF0,
       0x01, 0x11, 0x21, 0x31, 0x41, 0x51, 0x61, 0x71,
       0x81, 0x91, 0xA1, 0xB1, 0xC1, 0xD1, 0xE1, 0xF1,
       0x02, 0x12, 0x22, 0x32, 0x42, 0x52, 0x62, 0x72,
       0x82, 0x92, 0xA2, 0xB2, 0xC2, 0xD2, 0xE2, 0xF2,
       0x03, 0x13, 0x23, 0x33, 0x43, 0x53, 0x63, 0x73,
       0x83, 0x93, 0xA3, 0xB3, 0xC3, 0xD3, 0xE3, 0xF3,
       0x04, 0x14, 0x24, 0x34, 0x44, 0x54, 0x64, 0x74,
       0x84, 0x94, 0xA4, 0xB4, 0xC4, 0xD4, 0xE4, 0xF4,
       0x05, 0x15, 0x25, 0x35, 0x45, 0x55, 0x65, 0x75,
       0x85, 0x95, 0xA5, 0xB5, 0xC5, 0xD5, 0xE5, 0xF5,
       0x06, 0x16, 0x26, 0x36, 0x46, 0x56, 0x66, 0x76,
       0x86, 0x96, 0xA6, 0xB6, 0xC6, 0xD6, 0xE6, 0xF6,
       0x07, 0x17, 0x27, 0x37, 0x47, 0x57, 0x67, 0x77,
       0x87, 0x97, 0xA7, 0xB7, 0xC7, 0xD7, 0xE7, 0xF7,
       0x08, 0x18, 0x28, 0x38, 0x48, 0x58, 0x68, 0x78,
       0x88, 0x98, 0xA8, 0xB8, 0xC8, 0xD8, 0xE8, 0xF8,
       0x09, 0x19, 0x29, 0x39, 0x49, 0x59, 0x69, 0x79,
       0x89, 0x99, 0xA9, 0xB9, 0xC9, 0xD9, 0xE9, 0xF9,
       0x0A, 0x1A, 0x2A, 0x3A, 0x4A, 0x5A, 0x6A, 0x7A,
       0x8A, 0x9A, 0xAA, 0xBA, 0xCA, 0xDA, 0xEA, 0xFA,
       0x0B, 0x1B, 0x2B, 0x3B, 0x4B, 0x5B, 0x6B, 0x7B,
       0x8B, 0x9B, 0xAB, 0xBB, 0xCB, 0xDB, 0xEB, 0xFB,
       0x0C, 0x1C, 0x2C, 0x3C, 0x4C, 0x5C, 0x6C, 0x7C,
       0x8C, 0x9C, 0xAC, 0xBC, 0xCC, 0xDC, 0xEC, 0xFC,
       0x0D, 0x1D, 0x2D, 0x3D, 0x4D, 0x5D, 0x6D, 0x7D,
       0x8D, 0x9D, 0xAD, 0xBD, 0xCD, 0xDD, 0xED, 0xFD,
       0x0E, 0x1E, 0x2E, 0x3E, 0x4E, 0x5E, 0x6E, 0x7E,
       0x8E, 0x9E, 0xAE, 0xBE, 0xCE, 0xDE, 0xEE, 0xFE,
       0x0F, 0x1F, 0x2F, 0x3F, 0x4F, 0x5F, 0x6F, 0x7F,
       0x8F, 0x9F, 0xAF, 0xBF, 0xCF, 0xDF, 0xEF, 0xFF
    };

    /* Swaps pixel packing order within bytes */
    void /* PRIVATE */
    png_do_packswap(png_row_infop row_info, png_bytep row)
    {
       png_debug(1, "in png_do_packswap");

       if (row_info->bit_depth < 8)
       {
          png_bytep rp;
          png_const_bytep end, table;

          end = row + row_info->rowbytes;

          if (row_info->bit_depth == 1)
             table = onebppswaptable;

          else if (row_info->bit_depth == 2)
             table = twobppswaptable;

          else if (row_info->bit_depth == 4)
             table = fourbppswaptable;

          else
             return;

          for (rp = row; rp < end; rp++)
             *rp = table[*rp];
       }
    }
    #endif /* PNG_READ_PACKSWAP_SUPPORTED or PNG_WRITE_PACKSWAP_SUPPORTED */

    #if defined(PNG_WRITE_FILLER_SUPPORTED) || \
        defined(PNG_READ_STRIP_ALPHA_SUPPORTED)
    /* Remove a channel - this used to be 'png_do_strip_filler' but it used a
     * somewhat weird combination of flags to determine what to do.  All the calls
     * to png_do_strip_filler are changed in 1.5.2 to call this instead with the
     * correct arguments.
     *
     * The routine isn't general - the channel must be the channel at the start or
     * end (not in the middle) of each pixel.
     */
    void /* PRIVATE */
    png_do_strip_channel(png_row_infop row_info, png_bytep row, int at_start)
    {
       png_bytep sp = row; /* source pointer */
       png_bytep dp = row; /* destination pointer */
       png_bytep ep = row + row_info->rowbytes; /* One beyond end of row */

       /* At the start sp will point to the first byte to copy and dp to where
        * it is copied to.  ep always points just beyond the end of the row, so
        * the loop simply copies (channels-1) channels until sp reaches ep.
        *
        * at_start:        0 -- convert AG, XG, ARGB, XRGB, AAGG, XXGG, etc.
        *            nonzero -- convert GA, GX, RGBA, RGBX, GGAA, RRGGBBXX, etc.
        */

       /* GA, GX, XG cases */
       if (row_info->channels == 2)
       {
          if (row_info->bit_depth == 8)
          {
             if (at_start) /* Skip initial filler */
                ++sp;
             else          /* Skip initial channel and, for sp, the filler */
                sp += 2, ++dp;

             /* For a 1 pixel wide image there is nothing to do */
             while (sp < ep)
                *dp++ = *sp, sp += 2;

             row_info->pixel_depth = 8;
          }

          else if (row_info->bit_depth == 16)
          {
             if (at_start) /* Skip initial filler */
                sp += 2;
             else          /* Skip initial channel and, for sp, the filler */
                sp += 4, dp += 2;

             while (sp < ep)
                *dp++ = *sp++, *dp++ = *sp, sp += 3;

             row_info->pixel_depth = 16;
          }

          else
             return; /* bad bit depth */

          row_info->channels = 1;

          /* Finally fix the color type if it records an alpha channel */
          if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
             row_info->color_type = PNG_COLOR_TYPE_GRAY;
       }

       /* RGBA, RGBX, XRGB cases */
       else if (row_info->channels == 4)
       {
          if (row_info->bit_depth == 8)
          {
             if (at_start) /* Skip initial filler */
                ++sp;
             else          /* Skip initial channels and, for sp, the filler */
                sp += 4, dp += 3;

             /* Note that the loop adds 3 to dp and 4 to sp each time. */
             while (sp < ep)
                *dp++ = *sp++, *dp++ = *sp++, *dp++ = *sp, sp += 2;

             row_info->pixel_depth = 24;
          }

          else if (row_info->bit_depth == 16)
          {
             if (at_start) /* Skip initial filler */
                sp += 2;
             else          /* Skip initial channels and, for sp, the filler */
                sp += 8, dp += 6;

             while (sp < ep)
             {
                /* Copy 6 bytes, skip 2 */
                *dp++ = *sp++, *dp++ = *sp++;
                *dp++ = *sp++, *dp++ = *sp++;
                *dp++ = *sp++, *dp++ = *sp, sp += 3;
             }

             row_info->pixel_depth = 48;
          }

          else
             return; /* bad bit depth */

          row_info->channels = 3;

          /* Finally fix the color type if it records an alpha channel */
          if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
             row_info->color_type = PNG_COLOR_TYPE_RGB;
       }

       else
          return; /* The filler channel has gone already */

       /* Fix the rowbytes value. */
       row_info->rowbytes = dp-row;
    }
    #endif

    #if defined(PNG_READ_BGR_SUPPORTED) || defined(PNG_WRITE_BGR_SUPPORTED)
    /* Swaps red and blue bytes within a pixel */
    void /* PRIVATE */
    png_do_bgr(png_row_infop row_info, png_bytep row)
    {
       png_debug(1, "in png_do_bgr");

       if ((row_info->color_type & PNG_COLOR_MASK_COLOR))
       {
          png_uint_32 row_width = row_info->width;
          if (row_info->bit_depth == 8)
          {
             if (row_info->color_type == PNG_COLOR_TYPE_RGB)
             {
                png_bytep rp;
                png_uint_32 i;

                for (i = 0, rp = row; i < row_width; i++, rp += 3)
                {
                   png_byte save = *rp;
                   *rp = *(rp + 2);
                   *(rp + 2) = save;
                }
             }

             else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
             {
                png_bytep rp;
                png_uint_32 i;

                for (i = 0, rp = row; i < row_width; i++, rp += 4)
                {
                   png_byte save = *rp;
                   *rp = *(rp + 2);
                   *(rp + 2) = save;
                }
             }
          }

    #ifdef PNG_16BIT_SUPPORTED
          else if (row_info->bit_depth == 16)
          {
             if (row_info->color_type == PNG_COLOR_TYPE_RGB)
             {
                png_bytep rp;
                png_uint_32 i;

                for (i = 0, rp = row; i < row_width; i++, rp += 6)
                {
                   png_byte save = *rp;
                   *rp = *(rp + 4);
                   *(rp + 4) = save;
                   save = *(rp + 1);
                   *(rp + 1) = *(rp + 5);
                   *(rp + 5) = save;
                }
             }

             else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
             {
                png_bytep rp;
                png_uint_32 i;

                for (i = 0, rp = row; i < row_width; i++, rp += 8)
                {
                   png_byte save = *rp;
                   *rp = *(rp + 4);
                   *(rp + 4) = save;
                   save = *(rp + 1);
                   *(rp + 1) = *(rp + 5);
                   *(rp + 5) = save;
                }
             }
          }
    #endif
       }
    }
    #endif /* PNG_READ_BGR_SUPPORTED or PNG_WRITE_BGR_SUPPORTED */

    #if defined(PNG_READ_CHECK_FOR_INVALID_INDEX_SUPPORTED) || \
        defined(PNG_WRITE_CHECK_FOR_INVALID_INDEX_SUPPORTED)
    /* Added at libpng-1.5.10 */
    void /* PRIVATE */
    png_do_check_palette_indexes(png_structrp png_ptr, png_row_infop row_info)
    {
       if (png_ptr->num_palette < (1 << row_info->bit_depth) &&
          png_ptr->num_palette > 0) /* num_palette can be 0 in MNG files */
       {
          /* Calculations moved outside switch in an attempt to stop different
           * compiler warnings.  'padding' is in *bits* within the last byte, it is
           * an 'int' because pixel_depth becomes an 'int' in the expression below,
           * and this calculation is used because it avoids warnings that other
           * forms produced on either GCC or MSVC.
           */
          int padding = (-row_info->pixel_depth * row_info->width) & 7;
          png_bytep rp = png_ptr->row_buf + row_info->rowbytes;

          switch (row_info->bit_depth)
          {
             case 1:
             {
                /* in this case, all bytes must be 0 so we don't need
                 * to unpack the pixels except for the rightmost one.
                 */
                for (; rp > png_ptr->row_buf; rp--)
                {
                  if (*rp >> padding != 0)
                     png_ptr->num_palette_max = 1;
                  padding = 0;
                }

                break;
             }

             case 2:
             {
                for (; rp > png_ptr->row_buf; rp--)
                {
                  int i = ((*rp >> padding) & 0x03);

                  if (i > png_ptr->num_palette_max)
                     png_ptr->num_palette_max = i;

                  i = (((*rp >> padding) >> 2) & 0x03);

                  if (i > png_ptr->num_palette_max)
                     png_ptr->num_palette_max = i;

                  i = (((*rp >> padding) >> 4) & 0x03);

                  if (i > png_ptr->num_palette_max)
                     png_ptr->num_palette_max = i;

                  i = (((*rp >> padding) >> 6) & 0x03);

                  if (i > png_ptr->num_palette_max)
                     png_ptr->num_palette_max = i;

                  padding = 0;
                }

                break;
             }

             case 4:
             {
                for (; rp > png_ptr->row_buf; rp--)
                {
                  int i = ((*rp >> padding) & 0x0f);

                  if (i > png_ptr->num_palette_max)
                     png_ptr->num_palette_max = i;

                  i = (((*rp >> padding) >> 4) & 0x0f);

                  if (i > png_ptr->num_palette_max)
                     png_ptr->num_palette_max = i;

                  padding = 0;
                }

                break;
             }

             case 8:
             {
                for (; rp > png_ptr->row_buf; rp--)
                {
                   if (*rp > png_ptr->num_palette_max)
                      png_ptr->num_palette_max = (int) *rp;
                }

                break;
             }

             default:
                break;
          }
       }
    }
    #endif /* PNG_CHECK_FOR_INVALID_INDEX_SUPPORTED */

    #if defined(PNG_READ_USER_TRANSFORM_SUPPORTED) || \
        defined(PNG_WRITE_USER_TRANSFORM_SUPPORTED)
    #ifdef PNG_USER_TRANSFORM_PTR_SUPPORTED
    void PNGAPI
    png_set_user_transform_info(png_structrp png_ptr, png_voidp
       user_transform_ptr, int user_transform_depth, int user_transform_channels)
    {
       png_debug(1, "in png_set_user_transform_info");

       if (png_ptr == NULL)
          return;

    #ifdef PNG_READ_USER_TRANSFORM_SUPPORTED
       if ((png_ptr->mode & PNG_IS_READ_STRUCT) != 0 &&
          (png_ptr->flags & PNG_FLAG_ROW_INIT) != 0)
       {
          png_app_error(png_ptr,
                "info change after png_start_read_image or png_read_update_info");
          return;
       }
    #endif

       png_ptr->user_transform_ptr = user_transform_ptr;
       png_ptr->user_transform_depth = (png_byte)user_transform_depth;
       png_ptr->user_transform_channels = (png_byte)user_transform_channels;
    }
    #endif

    /* This function returns a pointer to the user_transform_ptr associated with
     * the user transform functions.  The application should free any memory
     * associated with this pointer before png_write_destroy and png_read_destroy
     * are called.
     */
    #ifdef PNG_USER_TRANSFORM_PTR_SUPPORTED
    png_voidp PNGAPI
    png_get_user_transform_ptr(png_const_structrp png_ptr)
    {
       if (png_ptr == NULL)
          return (NULL);

       return png_ptr->user_transform_ptr;
    }
    #endif

    #ifdef PNG_USER_TRANSFORM_INFO_SUPPORTED
    png_uint_32 PNGAPI
    png_get_current_row_number(png_const_structrp png_ptr)
    {
       /* See the comments in png.h - this is the sub-image row when reading and
        * interlaced image.
        */
       if (png_ptr != NULL)
          return png_ptr->row_number;

       return PNG_UINT_32_MAX; /* help the app not to fail silently */
    }

    png_byte PNGAPI
    png_get_current_pass_number(png_const_structrp png_ptr)
    {
       if (png_ptr != NULL)
          return png_ptr->pass;
       return 8; /* invalid */
    }
    #endif /* PNG_USER_TRANSFORM_INFO_SUPPORTED */
    #endif /* PNG_READ_USER_TRANSFORM_SUPPORTED ||
              PNG_WRITE_USER_TRANSFORM_SUPPORTED */
    #endif /* PNG_READ_SUPPORTED || PNG_WRITE_SUPPORTED */