+
+#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
+ /* Detect gray background and attempt to enable optimization
+ * for gray --> RGB case */
+ /* Note: if PNG_BACKGROUND_EXPAND is set and color_type is either RGB or
+ * RGB_ALPHA (in which case need_expand is superfluous anyway), the
+ * background color might actually be gray yet not be flagged as such.
+ * This is not a problem for the current code, which uses
+ * PNG_BACKGROUND_IS_GRAY only to decide when to do the
+ * png_do_gray_to_rgb() transformation.
+ */
+ if ((png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
+ !(color_type & PNG_COLOR_MASK_COLOR))
+ {
+ png_ptr->mode |= PNG_BACKGROUND_IS_GRAY;
+ } else if ((png_ptr->transformations & PNG_BACKGROUND) &&
+ !(png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
+ (png_ptr->transformations & PNG_GRAY_TO_RGB) &&
+ png_ptr->background.red == png_ptr->background.green &&
+ png_ptr->background.red == png_ptr->background.blue)
+ {
+ png_ptr->mode |= PNG_BACKGROUND_IS_GRAY;
+ png_ptr->background.gray = png_ptr->background.red;
+ }
+#endif
+