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: Original image of the Sculptor Galaxy, NGC253, before processing with the Zone Mask Filter

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 Filter

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 terrestrial 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.  Many images benefit from increased saturation after Zone Mask processing, so this can be easily controlled during the process.

Fade Result lowers the overall 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

It is recommended to begin by zooming in on the preview window to show more of the fine detail.  In this example (where the original image was 3 megapixels), 50% zoom was ideal.

Above:  Zoom in to show more detail for the first few steps

The first thing to adjust is the Radius slider.  A higher Radius value will tend to bring out more structure in the object, but black halos can appear around bright stars if the value is too large.  try to zoom in on a bright star (such as the two at the left in this example) and select the largest radius that does not result in black halos.  In this case, a value of 12 was ideal.  A few small halos around smaller stars is okay, as this can be fixed with later steps.

Above:  Radius slider set to 12

The next step is usually to adjust the White Max slider.  This is normally decreased (which will brighten the image) until the very brightest parts of the picture (the bright stars and very core of the galaxy in this example) have just become pure white.  This sets an appropriate brightness for the mask levels.

Above: White Max decreased to 160

Now, jump down to the White Point slider to brighten the image to an appropriate level.  Decrease the slider to brighten the image without blowing out any of the highlights.  This may need to be adjusted again later, after other steps, but this initial adjustment will get you in the ballpark and produce a reasonable-looking image.

Above:  White Point slider decreased to 155

At this point, it is recommended to zoom out the preview window until the entire image can be seen.  The remaining adjustments will apply to the image as a whole, including the background, so it is best to see the entire picture.

Above:  Zoom out to see the entire image

Adjust the Mid Point slider to darken the middle tones of the image and darken the background.  Normally the Mid Point needs to be increased.  It may be necessary to go back and adjust the White Point at this point.  The Black Point can be adjusted as well to darken the background.  However, increasing the Black Point too much can result in histogram clipping, where faint detail is lost.  Better to leave the background a little light then apply Curves in Photoshop after the filter has been run if necessary.

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 40

At this point, if the effect is too strong, the Fade Result slider can be adjusted.  Usually a setting of 20 to 30 works well, but it depends very much on the image.  Some images are best without any Fade, and some work well with a setting of 30 to 50.  The Fade Result slider will eliminate the remaining black halos around the smallest stars.

Above:  Fade Result slider set to 20

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

Above:  NGC253 after Zone Mask Filter processing

Return to Zone Mask Filter Page