The Zone Mask Filter works by selectively brightening faint detail, compressing bright tonal ranges, enhancing detail, and sharpening the image.  All this control is provided in a simple window with a few sliders.  The range of results is very broad, and different images will require different settings.  This tutorial will give an overview of all the functions and what effects they have on the final image, allowing the user to easily process any type of image.

Processing Images with the Zone Mask Filter

Above:  Zion Canyon Waterfall, original unprocessed image captured with Canon EOS 10D camera and 17-40mm f/4L lens

Begin by opening the image in Photoshop, then open the Zone Mask Filter window by selecting Filter > Starizona > Zone Mask.

Above:  Default settings for the Zone Mask Filters

The default settings try to give a reasonable image right from the start, but the filter is designed to work with a wide range of image types, including astronomical photos, so if the results look a little bizarre to begin with, don't worry.

Tip:  At any time, you can simply click on the preview image to show the original, unprocessed image.  This is an easy way to check the results of the filter settings.

How the Zone Mask Filter Works

There are four sets of sliders in the Zone Mask window.  Each setting and how it is applied will be covered in detail below, but a brief overview is given here for clarity. 

The Mask Adjustments control the parameters of the mask that is applied to the image.  The Brightness slider rarely needs to be adjusted.  Increasing it will brighten the overall image, but this is better done with other sliders.  White Max, Gamma and Radius are the three most important sliders in the Zone Mask Filter.  They control mask parameters that have a significant effect on the resulting image.  In general, decreasing the White Max slider will brighten the highlights of the image.  Changing the Gamma controls how much bright details are compressed into a narrower tonal range.  The full effect of these sliders is seen in the example below.  Radius controls the amount of blur applied to the mask.  This has considerable effect on the enhancement of detail in the final image.

The Level Adjustments control the brightness of the final image.  They apply to the resulting image, not the mask.  Black Point rarely needs to be changed.  Mid Point and White Point are often adjusted.  These works basically like the Levels function in Photoshop.  Decreasing the White Point brightens the image.  Increasing the Mid Point darkens the middle tones of the image.  These sliders are critical in getting an aesthetically pleasing result.

Color Balance does exactly what the same function does in Photoshop.  However, it is handy to have these built into the Zone Mask filter.  The Red, Green, and Blue setting do not often need to be changed, as Zone Mask is designed to preserve the initial colors of the original image.  But Zone Mask has enough control that it is recommended as a first processing step before Levels, Curves, or any other of the usual Photoshop features are used on an image.  Since a raw image may not have been color-corrected, these sliders are often useful.  The Saturation slider is set to a default above the normal saturation level.  It was found that many images benefit from increased saturation after Zone Mask processing, so this can be easily controlled during the process.

Fade Result lowers the strength of the filter.  In some cases, where a more subtle effect is desired, this can be very useful.  It works the same way as the Fade function in Photoshop, but again it is useful to have built into the Zone Mask Filter so the results can be seen before the filter is applied.

Processing Example

One of the most critical settings for terrestrial photos--and the first thing that should be adjusted--is the Radius slider.  This is especially true for photos that include a bright blue sky.  Too large a Radius setting will produce a halo artifact along the horizon line.  However, the Radius setting controls the amount of sharpening and the enhancement of midtone details.  It is best to select the largest Radius that does not produce a halo.

Zoom in to 100% in the preview window and move the preview image (click and drag) if necessary to find a distinct horizon line.  Adjust the Radius slider to minimize any halo effect.

Above:  Radius set to 10.  Note the distinct halo effect along the edge of the cliff.

Above:  Radius reduced to 3.  The halo effect is gone.

The next step is to adjust the White Max slider.  Normally this needs to be decreased to brighten the image.  If possible, find a bright highlight in the image, such as the water droplets in this example.  Adjust the White Max slider until the highlights just become pure white.  This will set the mask brightness levels to the appropriate values.

Above:  White Max slider set to 150

Next, find an area of the image with some midtones, such as the trees and cliffs in this example.  If necessary, adjust the Gamma slider at this point to change the middle tone values.  Decreasing the Gamma will result in a compressed tonal range.  This is especially useful for images with a very broad tonal range, such as those taken during the middle of the day when the lighting is less than optimal (as is the case with this example).  Any bright white features which appear overexposed may have detail returned to them by adjusting the Gamma slider.  This particular example does not benefit from much Gamma adjustment since the default is just about right.

While viewing the middle tone area, adjust the White Point slider to brighten the image to an appropriate level.  Make sure the highlights do not wash out, but look for the brighter midtone values, such as the tan-colored cliffs on the far side of the canyon in this example.  If the middle values get a little too bright, that's okay because the next step will correct that.

Above:  White Point slider set to 155

Increase the Mid Point slider to darken the middle values that may have been brightened excessively by adjusting the White Point slider.  This will give a better tonal range to the whole image.  The Black Point slider rarely needs to be adjusted.  Doing so can cause histogram clipping, which results in detail in shadow areas being lost.  Better to leave the shadows a tad too bright and adjust the final processed image with Curves in Photoshop if necessary.  Normally, this is not required.

Tip:  Often it is necessary to adjust the White Max, Gamma, White Point, and Mid Point sliders in an iterative process.  If things look a little off after setting the Level Adjustment sliders, go back to the White Max and Gamma and see if moving the sliders helps.

Above:  Mid Point increased to 30

The final step is to adjust the Saturation if needed.  Some images benefit from having the saturation increased to the default value of 1.5 after the Zone Mask process.  However, this image was fairly saturated to start, so the default level was lowered to 1.3.  Any Color Balance changes can be made at this point as well.

Above:  Saturation slider reduced to 1.3

Tip:  The Zone Mask Filter retains the last settings made after you run the filter.  So if you don't like the results, reopen the Zone Mask Filter and the previous settings will be there so you can easily make minor changes.  Clicking the Reset button at the top of the Zone Mask window will return the settings to their defaults.  Settings are not retained if Photoshop is closed and reopened.

Final Image

Below is the result of the Zone Mask Filter.  Compare to the original and note the enhancements.  Detail has been brought out in the washed out highlights of the waterfall.  The shadow areas in the trees and cliff on the near side of the canyon (at right) have been opened up to show more detail.  Midtone detail in the trees has been significantly improved.  The details along the cave roof above the waterfall are enhanced.  Detail on the far canyon wall (at lower left) is much improved, and the haziness is reduced.  An effect which is not seen so well in this smaller web image, but is apparent in the original 6 megapixel image, is a considerable sharpening of the image.  In fact, despite having been taken with an L-series Canon lens, stopped down to f/8, the original image looks a bit soft in comparison to the final result.  No noticeable noise or artifacts have been introduced, but the image is considerably improved.

Above:  Zion Canyon Waterfall after Zone Mask Filter processing

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