General orientation: The horizontal axis of the curve represents incoming image data, and the vertical axis represents outgoing data. In effect the curve window is an interactive graph, controlling the function that converts old image values to new ones. For example, in the above curve, an input value of 78 is converted to an output value of 137, and the result is brighter image values for a portion of the image.

The Channel Name describes the image data which is modified by the particular curve. This is usually an actual channel name such as Red, Green, or Blue, but it may also be the name of the Master Curve.

The Selected Control Point is outlined, and has its X Y axis highlighted with a pair of vertical and horizontal dotted lines.

The Axis Toggle diamond allows you to control the left-right orientation of the curve. In general, print oriented folks prefer to have black on the right, to represent increasing amounts of ink from left to right. Those who work with Photography and the Web, by convention, have white on the right to represent increasing brightness. Curvemeister.com recommends that you use black on the right for wg-CMYK mode, and white on the right for everything else.

The Numeric Edit Fields allow you to directly view and modify the in and out values of a particular control point

The Threshold Control is available to control the black and white cutoff points, using a graphically enhanced version of the image that makes it easy to discern pure white and black areas. When possible, Curvemeister.com recommends that you use the highlight and shadow points instead, for better color cast removal.

To use threshold functionality, click on the RGB, wg-CMYK, Brightness, or Lightness tab, and move the mouse to the extreme right or left side of the curve, or over one of the small triangular markers at any corner of the window. You will see the cursor change to , indicating that you may drag from side to side. Drag the mouse, and you will see a contrast enhanced version of your image, exaggerated to emphasize shadow or highlight detail. Press the alt key for an image like that of the Photoshop Levels command.

Notes:

• If you do not want an enhanced prevew image, click and drag on one of the curve endpoints instead of on the vertical edge of the curve.
• The threshold display does not always highlight clipped channel data. It highlights data that is greater than the assigned highlight value or less than the assigned shadow values. For example, if your highlight is RGB(245,245,245), the threshold display will highlight individual channel data that is greater than 245.
• If the highlight is set to the default value RGB(255,255,255), and the alt key is pressed, the displayed image is similar, if not identical, to that of Photoshop's Levels command.

CurveGuard and CurveAlert. Normally, it's a no-no to have the curve slope downward. Should you try to create such a curve, Curvemeister.com's CurveAlert warns you by highlighting the curve in red. CuveGuard may be disabled by un-checking the Options>CurveGuard menu item in either the Curve Right-Click Menu, or the Option Menu of the Main Menu.

In some situations, as for artistic effects, or when converting a negative to a positive, an inverted image is desirable - move the two endpoints to invert the curve, and Curvemeister will enforce a negative slope.

Axis Labels optionally label the curve in a using of several options, as determined by Axis Label and Grid Lines menu items. The example at the beginning of this section shows the photographic zone system, an homage to Ansel Adams.

The zone labels approximate a standard photographic convention by arbitrarily splitting the brightness range into 11 sections, labeled O to X.

An optional histogram showing a horizontal plot of the number of image pixel values.

The Curves right-click menu is accessed by right-clicking anywhere on the curve window. This menu is described in the Curves Right-Click Menu section.