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         png_chunk_report(png_ptr, "gamma value does not match sRGB",
            PNG_CHUNK_ERROR);
         /* Do not overwrite an sRGB value */
         return from == 2;
      }

      else /* sRGB tag not involved */
      {
         png_chunk_report(png_ptr, "gamma value does not match libpng estimate",
            PNG_CHUNK_WARNING);
         return from == 1;
      }
   }

   return 1;
}

void /* PRIVATE */
png_colorspace_set_gamma(png_const_structrp png_ptr,
   png_colorspacerp colorspace, png_fixed_point gAMA)
{
   /* Changed in libpng-1.5.4 to limit the values to ensure overflow can't
    * occur.  Since the fixed point representation is asymetrical it is
    * possible for 1/gamma to overflow the limit of 21474 and this means the
    * gamma value must be at least 5/100000 and hence at most 20000.0.  For
    * safety the limits here are a little narrower.  The values are 0.00016 to
    * 6250.0, which are truly ridiculous gamma values (and will produce
    * displays that are all black or all white.)
    *
    * In 1.6.0 this test replaces the ones in pngrutil.c, in the gAMA chunk
    * handling code, which only required the value to be >0.
    */
   png_const_charp errmsg;

   if (gAMA < 16 || gAMA > 625000000)
      errmsg = "gamma value out of range";

#  ifdef PNG_READ_gAMA_SUPPORTED
      /* Allow the application to set the gamma value more than once */
      else if ((png_ptr->mode & PNG_IS_READ_STRUCT) != 0 &&
         (colorspace->flags & PNG_COLORSPACE_FROM_gAMA) != 0)
         errmsg = "duplicate";
#  endif

   /* Do nothing if the colorspace is already invalid */
   else if ((colorspace->flags & PNG_COLORSPACE_INVALID) != 0)
      return;

   else
   {
      if (png_colorspace_check_gamma(png_ptr, colorspace, gAMA,
          1/*from gAMA*/) != 0)
      {
         /* Store this gamma value. */
         colorspace->gamma = gAMA;
         colorspace->flags |=
            (PNG_COLORSPACE_HAVE_GAMMA | PNG_COLORSPACE_FROM_gAMA);
      }

      /* At present if the check_gamma test fails the gamma of the colorspace is
       * not updated however the colorspace is not invalidated.  This
       * corresponds to the case where the existing gamma comes from an sRGB
       * chunk or profile.  An error message has already been output.
       */
      return;
   }

   /* Error exit - errmsg has been set. */
   colorspace->flags |= PNG_COLORSPACE_INVALID;
   png_chunk_report(png_ptr, errmsg, PNG_CHUNK_WRITE_ERROR);
}

void /* PRIVATE */
png_colorspace_sync_info(png_const_structrp png_ptr, png_inforp info_ptr)
{
   if ((info_ptr->colorspace.flags & PNG_COLORSPACE_INVALID) != 0)
   {
      /* Everything is invalid */
      info_ptr->valid &= ~(PNG_INFO_gAMA|PNG_INFO_cHRM|PNG_INFO_sRGB|
         PNG_INFO_iCCP);

#     ifdef PNG_COLORSPACE_SUPPORTED
         /* Clean up the iCCP profile now if it won't be used. */
         png_free_data(png_ptr, info_ptr, PNG_FREE_ICCP, -1/*not used*/);
#     else
         PNG_UNUSED(png_ptr)
#     endif
   }

   else
   {
#     ifdef PNG_COLORSPACE_SUPPORTED
         /* Leave the INFO_iCCP flag set if the pngset.c code has already set
          * it; this allows a PNG to contain a profile which matches sRGB and
          * yet still have that profile retrievable by the application.
          */
         if ((info_ptr->colorspace.flags & PNG_COLORSPACE_MATCHES_sRGB) != 0)
            info_ptr->valid |= PNG_INFO_sRGB;

         else
            info_ptr->valid &= ~PNG_INFO_sRGB;

         if ((info_ptr->colorspace.flags & PNG_COLORSPACE_HAVE_ENDPOINTS) != 0)
            info_ptr->valid |= PNG_INFO_cHRM;

         else
            info_ptr->valid &= ~PNG_INFO_cHRM;
#     endif

      if ((info_ptr->colorspace.flags & PNG_COLORSPACE_HAVE_GAMMA) != 0)
         info_ptr->valid |= PNG_INFO_gAMA;

      else
         info_ptr->valid &= ~PNG_INFO_gAMA;
   }
}

#ifdef PNG_READ_SUPPORTED
void /* PRIVATE */
png_colorspace_sync(png_const_structrp png_ptr, png_inforp info_ptr)
{