Two-Zone Adjustment

This transformation can be used to independently adjust the brightness, contrast and saturation of two different tonal zones of an image. The first step is to set a brightness level that divides the shadow zone from the highlight zone. Having done this, you can proceed to adjust each zone independently. Finally, the two 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 third mask for the so-called transition zone between the shadow 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 three masks to produce the result.

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 marker sets the boundary between the highlight and shadow zones. For best results, it 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.

Blur Radius

This slider lets you control how soft the edges of the masks will be. Adjusting the blur radius can help reduce halos at the boundaries between the highlight and shadow zones.

Contrast, Brightness and Saturation

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

Highlight Amount, Shadow Amount, and Transition Amount

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

Tips

The key to using this transformation is to work in stages. This is illustrated with the following example image:

The problem with this image is muddy shadows and highlights. Using a single tone curve, it is usually impossible to fix both of these problems at once since increasing the shadow contrast descreses the hightlight contrast and vice versa.

Stage 1: set the zone boundaries

Since the image uses the full range from black to white, we can leave the black and white histogram markers alone. We then adjust the gray marker by eye using the Zone display mode to achieve good separation between highlights and shadows. Once this is done, we can switch the display to After mode so we can see the output image we are creating.

Stage 2: adjust the highlights

Click the Highlight tab to expose the highlight controls and adjust the contrast, brightness and saturation to get the effect you want. Focus on the effect on the image highlights and the changes will not be applied to the shadow areas anyway. By switching between Before and After display modes you can see the effect your changes are making.

Stage 3: adjust the shadows

Click the Shadow tab to expose the shadow controls and adjust the contrast, brightness and saturation to get the effect you want. Focus on the effect on the image shadows and the changes will not be applied to the highlight areas anyway. By switching between Before and After display modes you can see the effect your changes are making.

Stage 4: blend the highlight and shadow changes

Click the Blend tab to expose the blend controls and adjust the blur radius, highlight amount, shadow amount, and transition amount to get the effect you want. By switching between Before and After display modes you can see the effect your changes are making. The highlight and shadow amount sliders let you scale back the amount of highlight or shadow adjustment if the results are too extreme. If there are visible halos on the boundary between shadow and highlights, try varying the blur radius and transition amount.

Stage 5: refinements

If necessary, you may have to go back and adjust the highlight and/or shadow brightness to make the transition between the two less obvious.