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libpng-1.6.17/contrib/libtests/pngvalid.c  view on Meta::CPAN

   /* Modifications (not necessarily used.) */
   gama_modification gama_mod;
   chrm_modification chrm_mod;
   srgb_modification srgb_mod;
} transform_display;

/* Set sRGB, cHRM and gAMA transforms as required by the current encoding. */
static void
transform_set_encoding(transform_display *this)
{
   /* Set up the png_modifier '_current' fields then use these to determine how
    * to add appropriate chunks.
    */
   png_modifier *pm = this->pm;

   modifier_set_encoding(pm);

   if (modifier_color_encoding_is_set(pm))
   {
      if (modifier_color_encoding_is_sRGB(pm))
         srgb_modification_init(&this->srgb_mod, pm, PNG_sRGB_INTENT_ABSOLUTE);

      else
      {
         /* Set gAMA and cHRM separately. */
         gama_modification_init(&this->gama_mod, pm, pm->current_gamma);

         if (pm->current_encoding != 0)
            chrm_modification_init(&this->chrm_mod, pm, pm->current_encoding);
      }
   }
}

/* Three functions to end the list: */
static void
image_transform_ini_end(PNG_CONST image_transform *this,
   transform_display *that)
{
   UNUSED(this)
   UNUSED(that)
}

static void
image_transform_set_end(PNG_CONST image_transform *this,
   transform_display *that, png_structp pp, png_infop pi)
{
   UNUSED(this)
   UNUSED(that)
   UNUSED(pp)
   UNUSED(pi)
}

/* At the end of the list recalculate the output image pixel value from the
 * double precision values set up by the preceding 'mod' calls:
 */
static unsigned int
sample_scale(double sample_value, unsigned int scale)
{
   sample_value = floor(sample_value * scale + .5);

   /* Return NaN as 0: */
   if (!(sample_value > 0))
      sample_value = 0;
   else if (sample_value > scale)
      sample_value = scale;

   return (unsigned int)sample_value;
}

static void
image_transform_mod_end(PNG_CONST image_transform *this, image_pixel *that,
    png_const_structp pp, PNG_CONST transform_display *display)
{
   PNG_CONST unsigned int scale = (1U<<that->sample_depth)-1;
   PNG_CONST int sig_bits = that->sig_bits;

   UNUSED(this)
   UNUSED(pp)
   UNUSED(display)

   /* At the end recalculate the digitized red green and blue values according
    * to the current sample_depth of the pixel.
    *
    * The sample value is simply scaled to the maximum, checking for over
    * and underflow (which can both happen for some image transforms,
    * including simple size scaling, though libpng doesn't do that at present.
    */
   that->red = sample_scale(that->redf, scale);

   /* This is a bit bogus; really the above calculation should use the red_sBIT
    * value, not sample_depth, but because libpng does png_set_shift by just
    * shifting the bits we get errors if we don't do it the same way.
    */
   if (sig_bits && that->red_sBIT < that->sample_depth)
      that->red >>= that->sample_depth - that->red_sBIT;

   /* The error value is increased, at the end, according to the lowest sBIT
    * value seen.  Common sense tells us that the intermediate integer
    * representations are no more accurate than +/- 0.5 in the integral values,
    * the sBIT allows the implementation to be worse than this.  In addition the
    * PNG specification actually permits any error within the range (-1..+1),
    * but that is ignored here.  Instead the final digitized value is compared,
    * below to the digitized value of the error limits - this has the net effect
    * of allowing (almost) +/-1 in the output value.  It's difficult to see how
    * any algorithm that digitizes intermediate results can be more accurate.
    */
   that->rede += 1./(2*((1U<<that->red_sBIT)-1));

   if (that->colour_type & PNG_COLOR_MASK_COLOR)
   {
      that->green = sample_scale(that->greenf, scale);
      if (sig_bits && that->green_sBIT < that->sample_depth)
         that->green >>= that->sample_depth - that->green_sBIT;

      that->blue = sample_scale(that->bluef, scale);
      if (sig_bits && that->blue_sBIT < that->sample_depth)
         that->blue >>= that->sample_depth - that->blue_sBIT;

      that->greene += 1./(2*((1U<<that->green_sBIT)-1));
      that->bluee += 1./(2*((1U<<that->blue_sBIT)-1));
   }