Luminance Masking - Page 4
What is wrong with using a curve that is shaped like that? Well, for the majority of images, the local contrast found in the midtone region is what makes or breaks an image. This will determine whether or not the image has that "snap" to it.
When we make a curve steeper (more vertical), there is a more abrupt transition in tone. The image will gain contrast in that tonal region. If the curve is made flatter, then there is a more subtle transition in tone. The image will take on the appearance of being flat and lifeless. Below is how the image would appear if the curve that flattened the midtones was applied. Click to see the "before" version.
Curves that flatten the midtones will not improve our images.