+ /* Prevent the transformations being done again, and make sure
+ * that the now spurious alpha channel is stripped - the code
+ * has just reduced background composition and gamma correction
+ * to a simple alpha channel strip.
+ */
+ png_ptr->transformations &= ~PNG_BACKGROUND;
+ png_ptr->transformations &= ~PNG_GAMMA;
+ png_ptr->transformations |= PNG_STRIP_ALPHA;