The Contrast slider serves to alter the effective contrast of the control curve(s) selected for editing. This can be done in various ways:
The contrast of the control curve(s) selected for editing is altered in a linear manner. This mainly alters the lightest and darkest portions of the image while the mid-tones remain constant.
To make linear contrast changes, just click the left mouse button on the arrows at the right or left ends of the bar for small changes, or on the shaded portions of the slider for larger changes. Alternatively you can grab the small white slider field with the left mouse button and drag it to a new position. (In other words, it behaves exactly like the standard GEM window sliders.)
The contrast of the control curve(s) being edited is altered in a manner where the lightest and darkest retain their values in the same way as the mid-tones, while the difference between the lightest and mid-tones and mid-tones and darkest ones is altered.
For using the gamma correction the [Alt] key must be held down for all actions while clicking on the arrows or dragging the slider.
Double-clicking on the white slider (in any position) brings up
a popup where the desired change can also be input numerically. The
measurement unit changes between p
(curve points) and %
according to the selection made in the Edit control points
dialog. If the [Alt] key is held down during the double-click, numeric
changes too will follow the gamma correction algorithm. Note that in
both cases the changes this produces are cumulative – i.e. they
refer to the current curve shape or position; positive values decrease
the contrast while negative values increase it. The slider position
does not change when making numeric changes, and may be used
independently.
