png.py 文件源码

def _process_pHYs(self, data):
        # http://www.w3.org/TR/PNG/#11pHYs
        self.phys = data
        fmt = "!LLB"
        if len(data) != struct.calcsize(fmt):
            raise FormatError("pHYs chunk has incorrect length.")
        self.x_pixels_per_unit, self.y_pixels_per_unit, unit = struct.unpack(fmt,data)
        self.unit_is_meter = bool(unit)