Three-Zone Adjustment

This transformation can be used to independently adjust the brightness, contrast and saturation of three different tonal zones of an image. The first step is to set brightness levels that divides the shadow zone from mid-tone zone and the mid-tone zone from the highlight zone. Having done this, you can proceed to adjust each zone independently. Finally, the three adjusted zones are blended to produce the result image. It is possible to achieve results using this transformation that are difficult or impossible to create by manipulating the image as a single zone.

The transformation works by creating a mask for each zone and a two additional masks for the so-called transition zones between the shadow and mid-tone and mid-tone and highlight zones. Adjustments to each zone are made only to the masked areas for that zone. Finally, the adjusted images are blended with the original image based on the five masks to produce the result.

If the image does not break down easily into light, medium and dark tonal zones, this transformation may not be your best choice.

Display Tool Bar

Zone display (Z)

Zone display is useful when setting zone markers (see below). It reduces each zone to an area of solid color based on which zone in the input image the pixels fall into. Thus, you can quickly see what parts of the image are in what zone.

Mask display (M)

Mask display shows the highlight, shadow, or blend masks depending on which tab is selected. This lets you see the masks the transformation is using and is helpful when setting the mask blur radius.

After (A)

After display shows the image after adjustment.

 To toggle between the input and output images, use the bypass buttons at the top of the dialog box.

Histogram and Zone Markers

This displays the brightness histogram of the input image and below it shows the location of the zone boundaries. If the image does not occupy the full range from black to white, you should drag the black and white markers in to just bracket the black and white points of the image. The intermediate gray markers set the boundary between the highlight/midtone and midtone/shadow zones. For best results, they should normally be placed at or near a local minimum of the histogram as this is a natural dividing point between zones. Use the Zone display (see above) to see how the image breaks down into zones as you adjust the markers. The three buttons in the upper right let you select different levels of histogram expansion to help you see small histogram values.

Shadow-Midtone and Midtone-Highlight Blur Radius

These sliders lets you control how soft the edges of the corresponding masks will be. Adjusting the blur radius can help reduce halos at the boundaries between adjacent zones.

Contrast, Brightness and Saturation

These sliders are displayed when the Highlight, Midtone or Shadow tabs are selected and let you adjust the contrast, brightness or saturation of the different zones.

Zone Amounts and Transition Amounts

These sliders are displayed when the Blend tab is selected and let you adjust the relative amounts of adjustment in the highlight, midtone and shadow or transition zones.