def convert_l_to_rgba(row, result):
            """Convert a grayscale image to RGBA. This method assumes
            the alpha channel in result is already correctly
            initialized.
            """
            for i in range(3):
                result[i::4] = row
Convert a grayscale image to RGBA. This method assumes
            the alpha channel in result is already correctly
            initialized.
            
png.py