PngImagePlugin.py 文件源码

def chunk_pHYs(self, pos, length):

        # pixels per unit
        s = ImageFile._safe_read(self.fp, length)
        px, py = i32(s), i32(s[4:])
        unit = i8(s[8])
        if unit == 1:  # meter
            dpi = int(px * 0.0254 + 0.5), int(py * 0.0254 + 0.5)
            self.im_info["dpi"] = dpi
        elif unit == 0:
            self.im_info["aspect"] = px, py
        return s