png_error(png_ptr, "Invalid bit depth for grayscale+alpha image");
         png_ptr->channels = 2;
         break;
      case PNG_COLOR_TYPE_RGB_ALPHA:
         if (bit_depth != 8 && bit_depth != 16)
            png_error(png_ptr, "Invalid bit depth for RGBA image");
         png_ptr->channels = 4;
         break;
      default:
         png_error(png_ptr, "Invalid image color type specified");
   }

   if (compression_type != PNG_COMPRESSION_TYPE_BASE)
   {
      png_warning(png_ptr, "Invalid compression type specified");
      compression_type = PNG_COMPRESSION_TYPE_BASE;
   }

   /* Write filter_method 64 (intrapixel differencing) only if
    * 1. Libpng was compiled with PNG_MNG_FEATURES_SUPPORTED and
    * 2. Libpng did not write a PNG signature (this filter_method is only
    *    used in PNG datastreams that are embedded in MNG datastreams) and
    * 3. The application called png_permit_mng_features with a mask that
    *    included PNG_FLAG_MNG_FILTER_64 and
    * 4. The filter_method is 64 and
    * 5. The color_type is RGB or RGBA
    */
   if (
#if defined(PNG_MNG_FEATURES_SUPPORTED)
      !((png_ptr->mng_features_permitted & PNG_FLAG_MNG_FILTER_64) &&
      ((png_ptr->mode&PNG_HAVE_PNG_SIGNATURE) == 0) &&
      (color_type == PNG_COLOR_TYPE_RGB ||
       color_type == PNG_COLOR_TYPE_RGB_ALPHA) &&
      (filter_type == PNG_INTRAPIXEL_DIFFERENCING)) &&
#endif
      filter_type != PNG_FILTER_TYPE_BASE)
   {
      png_warning(png_ptr, "Invalid filter type specified");
      filter_type = PNG_FILTER_TYPE_BASE;
   }

#ifdef PNG_WRITE_INTERLACING_SUPPORTED
   if (interlace_type != PNG_INTERLACE_NONE &&
      interlace_type != PNG_INTERLACE_ADAM7)
   {
      png_warning(png_ptr, "Invalid interlace type specified");
      interlace_type = PNG_INTERLACE_ADAM7;
   }
#else
   interlace_type=PNG_INTERLACE_NONE;
#endif

   /* save off the relevent information */
   png_ptr->bit_depth = (png_byte)bit_depth;
   png_ptr->color_type = (png_byte)color_type;
   png_ptr->interlaced = (png_byte)interlace_type;
#if defined(PNG_MNG_FEATURES_SUPPORTED)
   png_ptr->filter_type = (png_byte)filter_type;
#endif
   png_ptr->compression_type = (png_byte)compression_type;
   png_ptr->width = width;
   png_ptr->height = height;

   png_ptr->pixel_depth = (png_byte)(bit_depth * png_ptr->channels);
   png_ptr->rowbytes = PNG_ROWBYTES(png_ptr->pixel_depth, width);
   /* set the usr info, so any transformations can modify it */
   png_ptr->usr_width = png_ptr->width;
   png_ptr->usr_bit_depth = png_ptr->bit_depth;
   png_ptr->usr_channels = png_ptr->channels;

   /* pack the header information into the buffer */
   png_save_uint_32(buf, width);
   png_save_uint_32(buf + 4, height);
   buf[8] = (png_byte)bit_depth;
   buf[9] = (png_byte)color_type;
   buf[10] = (png_byte)compression_type;
   buf[11] = (png_byte)filter_type;
   buf[12] = (png_byte)interlace_type;

   /* write the chunk */
   png_write_chunk(png_ptr, (png_bytep)png_IHDR, buf, (png_size_t)13);

   /* initialize zlib with PNG info */
   png_ptr->zstream.zalloc = png_zalloc;
   png_ptr->zstream.zfree = png_zfree;
   png_ptr->zstream.opaque = (voidpf)png_ptr;
   if (!(png_ptr->do_filter))
   {
      if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE ||
         png_ptr->bit_depth < 8)
         png_ptr->do_filter = PNG_FILTER_NONE;
      else
         png_ptr->do_filter = PNG_ALL_FILTERS;
   }
   if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_STRATEGY))
   {
      if (png_ptr->do_filter != PNG_FILTER_NONE)
         png_ptr->zlib_strategy = Z_FILTERED;
      else
         png_ptr->zlib_strategy = Z_DEFAULT_STRATEGY;
   }
   if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_LEVEL))
      png_ptr->zlib_level = Z_DEFAULT_COMPRESSION;
   if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_MEM_LEVEL))
      png_ptr->zlib_mem_level = 8;
   if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_WINDOW_BITS))
      png_ptr->zlib_window_bits = 15;
   if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_METHOD))
      png_ptr->zlib_method = 8;
   deflateInit2(&png_ptr->zstream, png_ptr->zlib_level,
      png_ptr->zlib_method, png_ptr->zlib_window_bits,
      png_ptr->zlib_mem_level, png_ptr->zlib_strategy);
   png_ptr->zstream.next_out = png_ptr->zbuf;
   png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;

   png_ptr->mode = PNG_HAVE_IHDR;
}

/* write the palette.  We are careful not to trust png_color to be in the
 * correct order for PNG, so people can redefine it to any convenient
 * structure.
 */
void /* PRIVATE */
png_write_PLTE(png_structp png_ptr, png_colorp palette, png_uint_32 num_pal)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_PLTE;
#endif
   png_uint_32 i;
   png_colorp pal_ptr;
   png_byte buf[3];

   png_debug(1, "in png_write_PLTE\n");
   if ((
#if defined(PNG_MNG_FEATURES_SUPPORTED)
        !(png_ptr->mng_features_permitted & PNG_FLAG_MNG_EMPTY_PLTE) &&
#endif
        num_pal == 0) || num_pal > 256)
   {
     if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
     {
        png_error(png_ptr, "Invalid number of colors in palette");
     }
     else
     {
        png_warning(png_ptr, "Invalid number of colors in palette");
        return;
     }
   }

   if (!(png_ptr->color_type&PNG_COLOR_MASK_COLOR))
   {
      png_warning(png_ptr,
        "Ignoring request to write a PLTE chunk in grayscale PNG");
      return;
   }

   png_ptr->num_palette = (png_uint_16)num_pal;
   png_debug1(3, "num_palette = %d\n", png_ptr->num_palette);

   png_write_chunk_start(png_ptr, (png_bytep)png_PLTE, num_pal * 3);
#ifndef PNG_NO_POINTER_INDEXING
   for (i = 0, pal_ptr = palette; i < num_pal; i++, pal_ptr++)
   {
      buf[0] = pal_ptr->red;
      buf[1] = pal_ptr->green;
      buf[2] = pal_ptr->blue;
      png_write_chunk_data(png_ptr, buf, (png_size_t)3);
   }
#else
   /* This is a little slower but some buggy compilers need to do this instead */
   pal_ptr=palette;
   for (i = 0; i < num_pal; i++)
   {
      buf[0] = pal_ptr[i].red;
      buf[1] = pal_ptr[i].green;
      buf[2] = pal_ptr[i].blue;
      png_write_chunk_data(png_ptr, buf, (png_size_t)3);
   }
#endif
   png_write_chunk_end(png_ptr);
   png_ptr->mode |= PNG_HAVE_PLTE;
}

/* write an IDAT chunk */
void /* PRIVATE */
png_write_IDAT(png_structp png_ptr, png_bytep data, png_size_t length)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_IDAT;
#endif
   png_debug(1, "in png_write_IDAT\n");

   /* Optimize the CMF field in the zlib stream. */
   /* This hack of the zlib stream is compliant to the stream specification. */
   if (!(png_ptr->mode & PNG_HAVE_IDAT) &&
       png_ptr->compression_type == PNG_COMPRESSION_TYPE_BASE)
   {
      unsigned int z_cmf = data[0];  /* zlib compression method and flags */
      if ((z_cmf & 0x0f) == 8 && (z_cmf & 0xf0) <= 0x70)
      {
         /* Avoid memory underflows and multiplication overflows. */
         /* The conditions below are practically always satisfied;
            however, they still must be checked. */
         if (length >= 2 &&
             png_ptr->height < 16384 && png_ptr->width < 16384)
         {
            png_uint_32 uncompressed_idat_size = png_ptr->height *
               ((png_ptr->width *
               png_ptr->channels * png_ptr->bit_depth + 15) >> 3);
            unsigned int z_cinfo = z_cmf >> 4;
            unsigned int half_z_window_size = 1 << (z_cinfo + 7);
            while (uncompressed_idat_size <= half_z_window_size &&
                   half_z_window_size >= 256)
            {
               z_cinfo--;
               half_z_window_size >>= 1;
            }
            z_cmf = (z_cmf & 0x0f) | (z_cinfo << 4);
            if (data[0] != (png_byte)z_cmf)
            {
               data[0] = (png_byte)z_cmf;
               data[1] &= 0xe0;
               data[1] += (png_byte)(0x1f - ((z_cmf << 8) + data[1]) % 0x1f);
            }
         }
      }
      else
         png_error(png_ptr,
            "Invalid zlib compression method or flags in IDAT");
   }

   png_write_chunk(png_ptr, (png_bytep)png_IDAT, data, length);
   png_ptr->mode |= PNG_HAVE_IDAT;
}

/* write an IEND chunk */
void /* PRIVATE */
png_write_IEND(png_structp png_ptr)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_IEND;
#endif
   png_debug(1, "in png_write_IEND\n");
   png_write_chunk(png_ptr, (png_bytep)png_IEND, png_bytep_NULL,
     (png_size_t)0);
   png_ptr->mode |= PNG_HAVE_IEND;
}

#if defined(PNG_WRITE_gAMA_SUPPORTED)
/* write a gAMA chunk */
#ifdef PNG_FLOATING_POINT_SUPPORTED
void /* PRIVATE */
png_write_gAMA(png_structp png_ptr, double file_gamma)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_gAMA;
#endif
   png_uint_32 igamma;
   png_byte buf[4];

   png_debug(1, "in png_write_gAMA\n");
   /* file_gamma is saved in 1/100,000ths */
   igamma = (png_uint_32)(file_gamma * 100000.0 + 0.5);
   png_save_uint_32(buf, igamma);
   png_write_chunk(png_ptr, (png_bytep)png_gAMA, buf, (png_size_t)4);
}
#endif
#ifdef PNG_FIXED_POINT_SUPPORTED
void /* PRIVATE */
png_write_gAMA_fixed(png_structp png_ptr, png_fixed_point file_gamma)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_gAMA;
#endif
   png_byte buf[4];

   png_debug(1, "in png_write_gAMA\n");
   /* file_gamma is saved in 1/100,000ths */
   png_save_uint_32(buf, (png_uint_32)file_gamma);
   png_write_chunk(png_ptr, (png_bytep)png_gAMA, buf, (png_size_t)4);
}
#endif
#endif

#if defined(PNG_WRITE_sRGB_SUPPORTED)
/* write a sRGB chunk */
void /* PRIVATE */
png_write_sRGB(png_structp png_ptr, int srgb_intent)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_sRGB;
#endif
   png_byte buf[1];

   png_debug(1, "in png_write_sRGB\n");
   if(srgb_intent >= PNG_sRGB_INTENT_LAST)
         png_warning(png_ptr,
            "Invalid sRGB rendering intent specified");
   buf[0]=(png_byte)srgb_intent;
   png_write_chunk(png_ptr, (png_bytep)png_sRGB, buf, (png_size_t)1);
}
#endif

#if defined(PNG_WRITE_iCCP_SUPPORTED)
/* write an iCCP chunk */
void /* PRIVATE */
png_write_iCCP(png_structp png_ptr, png_charp name, int compression_type,
   png_charp profile, int profile_len)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_iCCP;
#endif
   png_size_t name_len;
   png_charp new_name;
   compression_state comp;

   png_debug(1, "in png_write_iCCP\n");
   if (name == NULL || (name_len = png_check_keyword(png_ptr, name,
      &new_name)) == 0)
   {
      png_warning(png_ptr, "Empty keyword in iCCP chunk");
      return;
   }

   if (compression_type != PNG_COMPRESSION_TYPE_BASE)
      png_warning(png_ptr, "Unknown compression type in iCCP chunk");

   if (profile == NULL)
      profile_len = 0;

   if (profile_len)
       profile_len = png_text_compress(png_ptr, profile, (png_size_t)profile_len,
          PNG_COMPRESSION_TYPE_BASE, &comp);

   /* make sure we include the NULL after the name and the compression type */
   png_write_chunk_start(png_ptr, (png_bytep)png_iCCP,
          (png_uint_32)name_len+profile_len+2);
   new_name[name_len+1]=0x00;
   png_write_chunk_data(png_ptr, (png_bytep)new_name, name_len + 2);

   if (profile_len)
      png_write_compressed_data_out(png_ptr, &comp);

   png_write_chunk_end(png_ptr);
   png_free(png_ptr, new_name);
}
#endif

#if defined(PNG_WRITE_sPLT_SUPPORTED)
/* write a sPLT chunk */
void /* PRIVATE */
png_write_sPLT(png_structp png_ptr, png_sPLT_tp spalette)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_sPLT;
#endif
   png_size_t name_len;
   png_charp new_name;
   png_byte entrybuf[10];
   int entry_size = (spalette->depth == 8 ? 6 : 10);
   int palette_size = entry_size * spalette->nentries;
   png_sPLT_entryp ep;
#ifdef PNG_NO_POINTER_INDEXING
   int i;
#endif

   png_debug(1, "in png_write_sPLT\n");
   if (spalette->name == NULL || (name_len = png_check_keyword(png_ptr,
      spalette->name, &new_name))==0)
   {
      png_warning(png_ptr, "Empty keyword in sPLT chunk");
      return;
   }

   /* make sure we include the NULL after the name */
   png_write_chunk_start(png_ptr, (png_bytep)png_sPLT,
          (png_uint_32)(name_len + 2 + palette_size));
   png_write_chunk_data(png_ptr, (png_bytep)new_name, name_len + 1);
   png_write_chunk_data(png_ptr, (png_bytep)&spalette->depth, 1);

   /* loop through each palette entry, writing appropriately */
#ifndef PNG_NO_POINTER_INDEXING
   for (ep = spalette->entries; ep<spalette->entries+spalette->nentries; ep++)
   {
       if (spalette->depth == 8)
       {
           entrybuf[0] = (png_byte)ep->red;
           entrybuf[1] = (png_byte)ep->green;
           entrybuf[2] = (png_byte)ep->blue;
           entrybuf[3] = (png_byte)ep->alpha;
           png_save_uint_16(entrybuf + 4, ep->frequency);
       }
       else
       {
           png_save_uint_16(entrybuf + 0, ep->red);
           png_save_uint_16(entrybuf + 2, ep->green);
           png_save_uint_16(entrybuf + 4, ep->blue);
           png_save_uint_16(entrybuf + 6, ep->alpha);
           png_save_uint_16(entrybuf + 8, ep->frequency);
       }
       png_write_chunk_data(png_ptr, entrybuf, (png_size_t)entry_size);
   }
#else
   ep=spalette->entries;
   for (i=0; i>spalette->nentries; i++)
   {
       if (spalette->depth == 8)
       {
           entrybuf[0] = (png_byte)ep[i].red;
           entrybuf[1] = (png_byte)ep[i].green;