[devel] Implement expansion to 16 bits

pngrtran.c

@@ -137,6 +137,7 @@ png_set_strip_16(png_structp png_ptr)
       return;
 
    png_ptr->transformations |= PNG_16_TO_8;
+   png_ptr->transformations &= ~PNG_EXPAND_16;
 }
 #endif
 
@@ -686,6 +687,25 @@ png_set_tRNS_to_alpha(png_structp png_ptr)
 }
 #endif /* defined(PNG_READ_EXPAND_SUPPORTED) */
 
+#ifdef PNG_READ_EXPAND_16_SUPPORTED
+/* Expand to 16 bit channels, expand the tRNS chunk too (because otherwise
+ * it may not work correctly.)
+ */
+void PNGAPI
+png_set_expand_16(png_structp png_ptr)
+{
+   png_debug(1, "in png_set_expand_16");
+
+   if (png_ptr == NULL)
+      return;
+
+   png_ptr->transformations |= (PNG_EXPAND_16 | PNG_EXPAND | PNG_EXPAND_tRNS);
+   png_ptr->transformations &= ~PNG_16_TO_8;
+
+   png_ptr->flags &= ~PNG_FLAG_ROW_INIT;
+}
+#endif
+
 #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
 void PNGAPI
 png_set_gray_to_rgb(png_structp png_ptr)
@@ -1285,6 +1305,14 @@ png_read_transform_info(png_structp png_ptr, png_infop info_ptr)
    }
 #endif
 
+#ifdef PNG_READ_EXPAND_16_SUPPORTED
+   if (png_ptr->transformations & PNG_EXPAND_16 && info_ptr->bit_depth == 8 &&
+      info_ptr->color_type != PNG_COLOR_TYPE_PALETTE)
+   {
+      info_ptr->bit_depth = 16;
+   }
+#endif
+
 #ifdef PNG_READ_BACKGROUND_SUPPORTED
    if (png_ptr->transformations & PNG_BACKGROUND)
    {
@@ -1445,14 +1473,17 @@ png_do_read_transformations(png_structp png_ptr)
              (png_ptr->transformations & PNG_EXPAND_tRNS))
             png_do_expand(&(png_ptr->row_info), png_ptr->row_buf + 1,
                 &(png_ptr->trans_color));
-         else
 
+         else
             png_do_expand(&(png_ptr->row_info), png_ptr->row_buf + 1,
                 NULL);
       }
    }
 #endif
 
+   /* Delay the 'expand 16' step until later for efficiency - so that the
+    * intermediate steps work with 8 bit data. */
+
 #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
    if ((png_ptr->transformations & PNG_STRIP_ALPHA) &&
       (png_ptr->row_info.color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
@@ -1567,6 +1598,16 @@ png_do_read_transformations(png_structp png_ptr)
    }
 #endif /* PNG_READ_QUANTIZE_SUPPORTED */
 
+#ifdef PNG_READ_EXPAND_16_SUPPORTED
+   /* Do the expansion now, after all the arithmetic has been done.  Notice
+    * that previous transformations can handle the PNG_EXPAND_16 flag if this
+    * is efficient (particularly true in the case of gamma correction, where
+    * better accuracy results faster!)
+    */
+   if (png_ptr->transformations & PNG_EXPAND_16)
+      png_do_expand_16(&png_ptr->row_info, png_ptr->row_buf + 1);
+#endif
+
 #ifdef PNG_READ_INVERT_SUPPORTED
    if (png_ptr->transformations & PNG_INVERT_MONO)
       png_do_invert(&(png_ptr->row_info), png_ptr->row_buf + 1);
@@ -1594,6 +1635,9 @@ png_do_read_transformations(png_structp png_ptr)
 #endif
 
 #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
+   /*NOTE: this must be in the wrong place - what happens if BGR is set too?
+    * Need pngvalid to test this combo.
+    */
    /* 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))
@@ -4066,6 +4110,37 @@ png_do_expand(png_row_infop row_info, png_bytep row,
 }
 #endif
 
+#ifdef PNG_READ_EXPAND_16_SUPPORTED
+/* If the bit depth is 8 and the colour type is not a palette type expand the
+ * whole row to 16 bits.  Has no effect otherwise.
+ */
+void /* PRIVATE */
+png_do_expand_16(png_row_infop row_info, png_bytep row)
+{
+   if (row_info->bit_depth == 8 &&
+      row_info->color_type != PNG_COLOR_TYPE_PALETTE)
+   {
+      /* The row have a sequence of bytes containing [0..255] and we need
+       * to turn it into another row containing [0..65535], to do this we
+       * calculate:
+       *
+       *  (input / 255) * 65535
+       *
+       *  Which happens to be exactly input * 257 and this can be achieved
+       *  simply by byte replication in place (copying backwards).
+       */
+      png_byte *sp = row + row_info->rowbytes; /* source, last byte + 1 */
+      png_byte *dp = sp + row_info->rowbytes;  /* destination, end + 1 */
+      while (dp > sp)
+         dp[-2] = dp[-1] = *--sp, dp -= 2;
+
+      row_info->rowbytes *= 2;
+      row_info->bit_depth = 16;
+      row_info->pixel_depth = (png_byte)(row_info->channels * 16);
+   }
+}
+#endif
+
 #ifdef PNG_READ_QUANTIZE_SUPPORTED
 void /* PRIVATE */
 png_do_quantize(png_row_infop row_info, png_bytep row,