A form of sharpening, this filter is a numerical imitation of a traditional film composite technique used to sharpen edges within an image. In a nutshell, the Unsharp Mask filter works by subtracting the blurred version of an image from the original. The filter corrects the blurring introduced during photographing, scanning, re-sampling or printing by increasing edge definition.
Instructions
- Open the Filter Browser, and add a new filter set using the small + icon located in the middle of the browser. This will create a new ‘untitled’ filter set for you. This will appear in the top section of the Filter Browser. If you already have filter sets created, clicking the + button will duplicate the selected filter set.
- Select Unsharp Mask… from the list of available filters in the lower section of the Filter Browser.
- Double click on the name of the new filter set in the top section of the browser, and name it appropriately.
- Edit the variables to achieve the result you need
- Amount - accepts percentages between 1 and 500. It determines how much darker and how much lighter the edge borders become.
- Radius - accepts pixels between 0.1 and 250. The radius controls how wide the edge rims become once the filter has been applied.
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Threshold - accepts numbers from 0 to 255. The threshold specifies how far apart adjacent tonal values should be before the filter processes the edges. Low threshold values will sharpen more as fewer areas are excluded. High threshold values will exclude areas of lower contrast. It is very easy to over sharpen images, and therefore the Threshold setting should be used cautiously.
In the snapshot below, the original data is on the left, and the filtered data is on the right.
Applying the filter
There are several ways to apply a filter:
- Click Apply - this will apply the filter to the active layer(s), and within a selection if there is one present in your file
- Click Make Layer - this will make a new layer in your file containing the filtered effect, leaving the original layer untouched
- Apply the filter using the Brush Tool - when you have finished building your filter set, simply close the Filter Browser. Then, open the Brushes Library, and select the filter you have just made from the drop down menu shown in the snapshot below. You can now paint with your filter.
Note: The default setting for the Brush Tool is ‘Brush”, located at the top of this drop down menu. To prevent you from becoming confused between the default setting and a filter setting, do not name any filters ‘Brush’. When you have finished painting with your filter, set the drop down menu back to the Brush setting, otherwise the Brush Tool may not behave as you would expect later on.