The plugin Curves 3, allows to apply a curve with easily controllable shape characteristics. With only three parameters (contrast, brightness, bias) , you can retouch pictures in a breeze. Additionally eight thumbnails allows an intuitive access to eight interesting presets.
version 2 : added three parameters to control the curve. Invert button and preserve hue option.
version 3: support for 64 bits. Added an Auto button that imitates Histogram Equalization, and a Pre-Normalize option.
Example 1: We pressed the Auto button, and we got the red curve (center). Notice that this curve is similar to the one applied, when performing an Histogram Equalization (blue, right).
We got this result after applying the red curve :
Advice : Usually, with the Auto button, you get a rough approximation of Histogram Equalization. This is a mere suggestion to improve contrast. If the result looks unnatural, readjust settings.
Example 2: If you apply a curve with extreme settings ( here : contrast=60, brightness=-30, bias=35) , some hue shifts can appear. On the right pic below, the orange turns to red. You can prevent this by checking the option "Preserve Hue" (center pic below) .
Curve + PH
Note: The option "Pre-Normalize" is equivalent to "Auto Contrast" command of Photoshop. It clips shadows and highlights values (by 0.2%), and then performs a linear transform to maximize contrast. A higher contrast can be achieved by pressing the "Auto" Button (combines linear and non-linear adjustments).