Method GTK2.GdkPixbuf()->add_alpha()

Method add_alpha: GTK2.GdkPixbuf add_alpha(int substitute_color, int r, int g, int b)
Description: Adds an alpha channel to this pixbuf and returns a copy. If it already has an alpha channel, the channel values are copied from the original; otherwise, the alpha channel is initialized to 255 (full opacity). If substitute_color is true, then the color specified by (r,g,b) will be assigned zero opacity. That is, if you pass (255,255,255) for the substitute color, all white pixels will become fully transparent.