pngrtran.c

一个国人自己实现图像库的程序（有参考价值）

      png_error(png_ptr, msg);
#else
      png_error(png_ptr, "NULL row buffer");
#endif
   }
#endif

#if defined(PNG_READ_EXPAND_SUPPORTED)
   if (png_ptr->transformations & PNG_EXPAND)
   {
      if (png_ptr->row_info.color_type == PNG_COLOR_TYPE_PALETTE)
      {
         png_do_expand_palette(&(png_ptr->row_info), png_ptr->row_buf + 1,
            png_ptr->palette, png_ptr->trans, png_ptr->num_trans);
      }
      else
      {
         if (png_ptr->num_trans)
            png_do_expand(&(png_ptr->row_info), png_ptr->row_buf + 1,
               &(png_ptr->trans_values));
         else
            png_do_expand(&(png_ptr->row_info), png_ptr->row_buf + 1,
               NULL);
      }
   }
#endif

#if defined(PNG_READ_STRIP_ALPHA_SUPPORTED)
   if (png_ptr->transformations & PNG_STRIP_ALPHA)
      png_do_strip_filler(&(png_ptr->row_info), png_ptr->row_buf + 1,
         PNG_FLAG_FILLER_AFTER);
#endif

#if defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
   if (png_ptr->transformations & PNG_RGB_TO_GRAY)
   {
      int rgb_error =
         png_do_rgb_to_gray(png_ptr, &(png_ptr->row_info), png_ptr->row_buf + 1);
      if(rgb_error)
      {
         png_ptr->rgb_to_gray_status=1;
         if(png_ptr->transformations == PNG_RGB_TO_GRAY_WARN)
            png_warning(png_ptr, "png_do_rgb_to_gray found nongray pixel");
         if(png_ptr->transformations == PNG_RGB_TO_GRAY_ERR)
            png_error(png_ptr, "png_do_rgb_to_gray found nongray pixel");
      }
   }
#endif

/*
From Andreas Dilger e-mail to png-implement, 26 March 1998:

  In most cases, the "simple transparency" should be done prior to doing
  gray-to-RGB, or you will have to test 3x as many bytes to check if a
  pixel is transparent.  You would also need to make sure that the
  transparency information is upgraded to RGB.

  To summarize, the current flow is:
  - Gray + simple transparency -> compare 1 or 2 gray bytes and composite
                                  with background "in place" if transparent,
                                  convert to RGB if necessary
  - Gray + alpha -> composite with gray background and remove alpha bytes,
                                  convert to RGB if necessary

  To support RGB backgrounds for gray images we need:
  - Gray + simple transparency -> convert to RGB + simple transparency, compare
                                  3 or 6 bytes and composite with background
                                  "in place" if transparent (3x compare/pixel
                                  compared to doing composite with gray bkgrnd)
  - Gray + alpha -> convert to RGB + alpha, composite with background and
                                  remove alpha bytes (3x float operations/pixel
                                  compared with composite on gray background)

  Greg's change will do this.  The reason it wasn't done before is for
  performance, as this increases the per-pixel operations.  If we would check
  in advance if the background was gray or RGB, and position the gray-to-RGB
  transform appropriately, then it would save a lot of work/time.
 */

#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
   /* if gray -> RGB, do so now only if background is non-gray; else do later
    * for performance reasons */
   if ((png_ptr->transformations & PNG_GRAY_TO_RGB) &&
       !(png_ptr->mode & PNG_BACKGROUND_IS_GRAY))
      png_do_gray_to_rgb(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_BACKGROUND_SUPPORTED)
   if ((png_ptr->transformations & PNG_BACKGROUND) &&
      ((png_ptr->num_trans != 0 ) ||
      (png_ptr->color_type & PNG_COLOR_MASK_ALPHA)))
      png_do_background(&(png_ptr->row_info), png_ptr->row_buf + 1,
         &(png_ptr->trans_values), &(png_ptr->background)
#if defined(PNG_READ_GAMMA_SUPPORTED)
         , &(png_ptr->background_1),
         png_ptr->gamma_table, png_ptr->gamma_from_1,
         png_ptr->gamma_to_1, png_ptr->gamma_16_table,
         png_ptr->gamma_16_from_1, png_ptr->gamma_16_to_1,
         png_ptr->gamma_shift
#endif
);
#endif

#if defined(PNG_READ_GAMMA_SUPPORTED)
   if ((png_ptr->transformations & PNG_GAMMA) &&
#if defined(PNG_READ_BACKGROUND_SUPPORTED)
      !((png_ptr->transformations & PNG_BACKGROUND) &&
      ((png_ptr->num_trans != 0) ||
      (png_ptr->color_type & PNG_COLOR_MASK_ALPHA))) &&
#endif
      (png_ptr->color_type != PNG_COLOR_TYPE_PALETTE))
      png_do_gamma(&(png_ptr->row_info), png_ptr->row_buf + 1,
         png_ptr->gamma_table, png_ptr->gamma_16_table,
         png_ptr->gamma_shift);
#endif

#if defined(PNG_READ_16_TO_8_SUPPORTED)
   if (png_ptr->transformations & PNG_16_TO_8)
      png_do_chop(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_DITHER_SUPPORTED)
   if (png_ptr->transformations & PNG_DITHER)
   {
      png_do_dither((png_row_infop)&(png_ptr->row_info), png_ptr->row_buf + 1,
         png_ptr->palette_lookup, png_ptr->dither_index);
      if(png_ptr->row_info.rowbytes == (png_uint_32)0)
         png_error(png_ptr, "png_do_dither returned rowbytes=0");
   }
#endif

#if defined(PNG_READ_INVERT_SUPPORTED)
   if (png_ptr->transformations & PNG_INVERT_MONO)
      png_do_invert(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_SHIFT_SUPPORTED)
   if (png_ptr->transformations & PNG_SHIFT)
      png_do_unshift(&(png_ptr->row_info), png_ptr->row_buf + 1,
         &(png_ptr->shift));
#endif

#if defined(PNG_READ_PACK_SUPPORTED)
   if (png_ptr->transformations & PNG_PACK)
      png_do_unpack(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_BGR_SUPPORTED)
   if (png_ptr->transformations & PNG_BGR)
      png_do_bgr(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_PACKSWAP_SUPPORTED)
   if (png_ptr->transformations & PNG_PACKSWAP)
      png_do_packswap(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
   /* if gray -> RGB, do so now only if we did not do so above */
   if ((png_ptr->transformations & PNG_GRAY_TO_RGB) &&
       (png_ptr->mode & PNG_BACKGROUND_IS_GRAY))
      png_do_gray_to_rgb(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_FILLER_SUPPORTED)
   if (png_ptr->transformations & PNG_FILLER)
      png_do_read_filler(&(png_ptr->row_info), png_ptr->row_buf + 1,
         (png_uint_32)png_ptr->filler, png_ptr->flags);
#endif

#if defined(PNG_READ_INVERT_ALPHA_SUPPORTED)
   if (png_ptr->transformations & PNG_INVERT_ALPHA)
      png_do_read_invert_alpha(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_SWAP_ALPHA_SUPPORTED)
   if (png_ptr->transformations & PNG_SWAP_ALPHA)
      png_do_read_swap_alpha(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_SWAP_SUPPORTED)
   if (png_ptr->transformations & PNG_SWAP_BYTES)
      png_do_swap(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_USER_TRANSFORM_SUPPORTED)
   if (png_ptr->transformations & PNG_USER_TRANSFORM)
    {
      if(png_ptr->read_user_transform_fn != NULL)
        (*(png_ptr->read_user_transform_fn)) /* user read transform function */
          (png_ptr,                    /* png_ptr */
           &(png_ptr->row_info),       /* row_info:     */
             /*  png_uint_32 width;          width of row */
             /*  png_uint_32 rowbytes;       number of bytes in row */
             /*  png_byte color_type;        color type of pixels */
             /*  png_byte bit_depth;         bit depth of samples */
             /*  png_byte channels;          number of channels (1-4) */
             /*  png_byte pixel_depth;       bits per pixel (depth*channels) */
           png_ptr->row_buf + 1);      /* start of pixel data for row */
#if defined(PNG_USER_TRANSFORM_PTR_SUPPORTED)
      if(png_ptr->user_transform_depth)
         png_ptr->row_info.bit_depth = png_ptr->user_transform_depth;
      if(png_ptr->user_transform_channels)
         png_ptr->row_info.channels = png_ptr->user_transform_channels;
#endif
      png_ptr->row_info.pixel_depth = (png_byte)(png_ptr->row_info.bit_depth *
         png_ptr->row_info.channels);
      png_ptr->row_info.rowbytes = (png_ptr->row_info.width *
         png_ptr->row_info.pixel_depth+7)>>3;
   }
#endif

}

#if defined(PNG_READ_PACK_SUPPORTED)
/* Unpack pixels of 1, 2, or 4 bits per pixel into 1 byte per pixel,
 * without changing the actual values.  Thus, if you had a row with
 * a bit depth of 1, you would end up with bytes that only contained
 * the numbers 0 or 1.  If you would rather they contain 0 and 255, use
 * png_do_shift() after this.
 */
void /* PRIVATE */
png_do_unpack(png_row_infop row_info, png_bytep row)
{
   png_debug(1, "in png_do_unpack\n");
#if defined(PNG_USELESS_TESTS_SUPPORTED)
   if (row != NULL && row_info != NULL && row_info->bit_depth < 8)
#else
   if (row_info->bit_depth < 8)
#endif
   {
      png_uint_32 i;
      png_uint_32 row_width=row_info->width;

      switch (row_info->bit_depth)
      {
         case 1:
         {
            png_bytep sp = row + (png_size_t)((row_width - 1) >> 3);
            png_bytep dp = row + (png_size_t)row_width - 1;
            png_uint_32 shift = 7 - (int)((row_width + 7) & 0x07);
            for (i = 0; i < row_width; i++)
            {
               *dp = (png_byte)((*sp >> shift) & 0x01);
               if (shift == 7)
               {
                  shift = 0;
                  sp--;
               }
               else
                  shift++;

               dp--;
            }
            break;
         }
         case 2:
         {

            png_bytep sp = row + (png_size_t)((row_width - 1) >> 2);
            png_bytep dp = row + (png_size_t)row_width - 1;
            png_uint_32 shift = (int)((3 - ((row_width + 3) & 0x03)) << 1);
            for (i = 0; i < row_width; i++)
            {
               *dp = (png_byte)((*sp >> shift) & 0x03);
               if (shift == 6)
               {
                  shift = 0;
                  sp--;
               }
               else
                  shift += 2;

               dp--;
            }
            break;
         }
         case 4:
         {
            png_bytep sp = row + (png_size_t)((row_width - 1) >> 1);
            png_bytep dp = row + (png_size_t)row_width - 1;
            png_uint_32 shift = (int)((1 - ((row_width + 1) & 0x01)) << 2);
            for (i = 0; i < row_width; i++)
            {
               *dp = (png_byte)((*sp >> shift) & 0x0f);
               if (shift == 4)
               {
                  shift = 0;
                  sp--;
               }
               else
                  shift = 4;

               dp--;
            }
            break;
         }
      }
      row_info->bit_depth = 8;
      row_info->pixel_depth = (png_byte)(8 * row_info->channels);
      row_info->rowbytes = row_width * row_info->channels;
   }
}
#endif

#if defined(PNG_READ_SHIFT_SUPPORTED)
/* Reverse the effects of png_do_shift.  This routine merely shifts the
 * pixels back to their significant bits values.  Thus, if you have
 * a row of bit depth 8, but only 5 are significant, this will shift
 * the values back to 0 through 31.
 */
void /* PRIVATE */
png_do_unshift(png_row_infop row_info, png_bytep row, png_color_8p sig_bits)
{
   png_debug(1, "in png_do_unshift\n");
   if (
#if defined(PNG_USELESS_TESTS_SUPPORTED)
       row != NULL && row_info != NULL && sig_bits != NULL &&
#endif
       row_info->color_type != PNG_COLOR_TYPE_PALETTE)
   {
      int shift[4];
      int channels = 0;
      int c;
      png_uint_16 value = 0;
      png_uint_32 row_width = row_info->width;

      if (row_info->color_type & PNG_COLOR_MASK_COLOR)
      {
         shift[channels++] = row_info->bit_depth - sig_bits->red;
         shift[channels++] = row_info->bit_depth - sig_bits->green;
         shift[channels++] = row_info->bit_depth - sig_bits->blue;
      }
      else
      {
         shift[channels++] = row_info->bit_depth - sig_bits->gray;
      }
      if (row_info->color_type & PNG_COLOR_MASK_ALPHA)
      {
         shift[channels++] = row_info->bit_depth - sig_bits->alpha;
      }

      for (c = 0; c < channels; c++)
      {
         if (shift[c] <= 0)
            shift[c] = 0;
         else
            value = 1;
      }

      if (!value)
         return;

      switch (row_info->bit_depth)
      {
         case 2:
         {
            png_bytep bp;
            png_uint_32 i;
            png_uint_32 istop = row_info->rowbytes;

            for (bp = row, i = 0; i < istop; i++)
            {
               *bp >>= 1;
               *bp++ &= 0x55;
            }
            break;
         }
         case 4:
         {
            png_bytep bp = row;
            png_uint_32 i;
            png_uint_32 istop = row_info->rowbytes;
            png_byte mask = (png_byte)((((int)0xf0 >> shift[0]) & (int)0xf0) |
               (png_byte)((int)0xf >> shift[0]));

            for (i = 0; i < istop; i++)
            {
               *bp >>= shift[0];