For landscape picture, it is sometimes very beneficial to get a soft imagetone to show more abundant details.
对于风景图像，有时也需要获得较柔和的影调，使图像的层次更为丰富多彩。
2
Soft imagetone can make portrait appearing more beautiful: the face wrinkles seem fade partly or completely, the skin becomes glossy and bright, thus people will look younger and pretty.
影像的柔化可使人像变得更漂亮，使人像的脸面皱纹减轻甚至消失，皮肤变得光滑滋润，因而显得年轻、亮丽。
3
The calotype was revolutionary in its use of chemically treated paper in which areas hit by light became dark in tone, producing a negative image.