The slider controls on the gradient bar below the histogram are the Output Level controls. These controls are used to set the range of colours used in the image:
You can use the Output Level controls to decrease the contrast in the image. For example, suppose that you set the minimum value to 100. A pixel with a colour value of 0 is remapped to 100. Pixels with colour values greater than 0 are remapped to the appropriate values. This has the effect of lightening the image and decreasing the contrast in the shadow areas.
Suppose that you set the maximum value for the range to 200. A pixel with a colour value of 255 is remapped to 200. Pixels with colour values less than 255 are remapped to the corresponding values. This has the effect of darkening the image and decreasing the contrast in the highlight areas.
You can also set the maximum and minimum limits for the colour range by setting the values directly in the Minimum and Maximum Output fields.
To reduce the contrast in an image:
The value of the lower limit for the colour range appears in the Minimum Output field.
The value of the upper limit appears in the Maximum Output field.