Generally
speaking, brightness, contrast, saturation and sharpness are thought to be the
four simplest controls as they have been developed as long as the color TV was
invented in the first place. However, people often turn blind eyes to the fact
that all these four controls are related to each other. As a matter of fact,
changing any one of these four controls will influence and change the other
three.
People
may tend to define sharpness as edge contrast, in other words, the contrast
along edges in a photo. It is reasonable for people to have such definition. The
fact is that an increase of sharpness will lead to the increase of the contrast
between only along/near edges in the photo while the smooth areas of the image
will not be influenced at all.
When
you have made use of the tool of unsharp mask, you will only change the
sharpness of the edges. In effect, different parts of the same image will show
different change of their sharpness. As a matter of fact, where the edge is
thicker, the sharpness will be increased while the contrast and brightness will
not have obvious change at all. If the edge is rather thin, then the contrast,
brightness and saturation will be greatly increased with the increase of the
sharpness. Therefore, it is safe to conclude that increasing sharpness can
cause the appearance of increase saturation, contrast, and brightness in areas
of the image which contain fine detail where other areas (areas with broader
detail) seem less affected except for the added sharpness. In all, changing one
of these four controls really affects the other three most of the time. Keep in
mind that you need to strike a balance between them; otherwise, the image will make
people feel uncomfortable.
