Curves

The Curves command (Image/Adjust) enables you to change the pixel values of an image. It allows you to focus with greater precision on certain tonal areas and is therefore more powerful than the Levels command (see Levels).

The "Curves" dialog consists of a tonal graph on a grid background. The tones of the image are altered by manipulating this graph in conjunction with the tonal range represented by a particular square or squares. The graph can take either of two forms: one which allows you to manipulate the graph by using points or markers, the other which enables you to draw a curve freehand. The two forms of curve can easily be converted into one another.

image\ppCurvesDlg.gif

The "Curves" dialog contains the following options:

The tones can be changed by clicking on the graph in the square that contains the relevant tones e.g. shades, mid-tones, highlights. A marker will appear on the graph at this point. There are two functions of markers. The first is to make tones lighter or darker by dragging the marker upwards or downwards respectively. The straight line graph will adjust to form a curve, using the marker as its point of origin, and the image will dynamically darken or lighten to reflect the new graph. With only one marker in place the whole graph bends into a curve and therefore affects the whole tonal range. Since you will usually want to concentrate on a limited range of tones, the second function of the markers is to anchor the graph, therefore restricting the curvature whenever you reposition a particular marker. To do this put several markers in place along the graph at regular intervals and then move the relevant marker up or down as required. Only a small section of the graph will be affected and hence only a small part of the tonal range will be altered. Note that the graph will attempt to form the smoothest curve possible between the markers when the Smooth curve option is set (see below for the difference between Smooth and Free curves).

You can place up to fourteen markers on the graph. Reposition a marker by dragging it along the graph in the required direction. Remove a marker by dragging it horizontally till it disappears (dragging vertically alters the graph itself, of course). Usually you will only need to make small adjustments to the graph, anything greater altering the image tones radically.

If you continually click on Smooth you will notice that the curve gradually straightens out, eventually returning to its original diagonal form.

Once you are satisfied click on OK to save the changes and exit the dialog; otherwise click on Cancel to exit without saving.

See:

Adjust Image