照相材料正确曝光时,其密度的增加和曝光量的大小相对应。但是,当曝光过度时,密度并不按曝光量的比例上升,相反会引起下降。图1是普通胶卷特性曲线,在最高密度点之后,曝光过量时,曲线反而下降,显然是密度降低了。这个下降部分就叫反转部分。在这部分所摄画面的明暗恰与原物相反, When the photographic material is correctly exposed, its density increases in proportion to the amount of exposure. However, when the exposure is excessive, the density does not increase in proportion to the amount of light exposure, but rather causes a decrease. Figure 1 is a typical film characteristics curve, after the highest density point, the exposure is over, the curve but decreased, apparently the density is reduced. This decline is called reverse part. In this part of the pictorial light and shade exactly opposite the original,