最后返回物理坐标系，并给出修改量计算公式。
A corresponding modification formula is provided for returning to the physical coordinate.
点的物理坐标是距离原点左上方的以像素为单位的实际偏移量。
The physical coordinates of a point are the actual offset in pixels from the top left of the origin.
viewport是一个人造的坐标系统，可以转换成图像的物理坐标系统。
A viewport is an artificial coordinate system that is translated into the physical coordinate system of the image.
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