Bilateral Sharpen

This transformation creates a sharpened version of the current image. Images are sharpened by exaggerating the difference between each pixel's value and a blurred version of the image. This make details stand out and gives the appearance of greater overall sharpness. Bilateral Sharpen supports as many as three sharpening passes using different parameters for each pass. This allows for sharpening the input image at different scales – a large blur radius sharpens coarse features while a small blur radius sharpens fine detail.

Amount

The amount control determines how much of the sharpen transformation is applied to the input image. You can apply a percentage of the transformation to the entire image, or you can specify an amount mask to restrict the effects of the transformation to only part of the input image.

Pass Buttons

These buttons let you activate or deactivate any of the three possible sharpening passes. You set the number of passes from the Settings Menu – buttons for passes that are inactive are grayed out. Turning passes on and off is a good way to check the effect of each pass as displayed in the preview area.

Halo Limit

This control has two sliders for limiting light and dark halos. Halos are sharpening artifacts and appear as light or dark areas around prominent edges in the input image. If you notice such a halo, reduce it by moving the appropriate slider to the left until the halo is no longer noticeable. Settings in the range of 5 - 15% are typical.

Blur Radius

The Blur Radius controls the degree of blurring performed using a bilateral technique that blurs detail but not across edges. This helps reduce halos and other sharpening artifacts.

The blur radius slider determines the scale of detail that will be sharpened. Small blur radius values sharpen fine detail while larger radius value work on larger image features such as clouds. It can be useful to use multiple sharpening passes with different radius settings.

Blur Threshold

This slider adjusts the threshold for inclusion in the blurring average. A threshold of zero reverts to simple sharpening and can result in halos around edges in the result image. Too high a threshold eliminates the blurring effect and thus results in little or no sharpening. A value around 30% to 40% usually works well for small blur radius settings, while smaller values work better for large blur radius values.

Sharpen Factor

The greater the Sharpen Factor, the more pronounced the sharpening effect. At 0.00 you get the blurred image; at 1.00 you get no sharpening; at higher values, you get increasing amounts of sharpening. Typical values are in the range from 1.25 to 2.50.

Sharpen Threshold

The sharpen threshold can be used to reduce the tendency to increase noise in the input image. When sharpening an image, the input image is first compared to a blurred version of the input image. If the absolute value of the difference is less than the threshold, no sharpening is done. Thus, a threshold of zero causes the entire image to be sharpened (except for regions partially or totally excluded by a mask). Large threshold values cause the sharpening to be applied only to very strong and sharp edges. A value of 0.00% yields full sharpening; higher values eliminate sharpening of increasingly coarse detail.

 Settings Menu

Number of Passes

This selects the number of sharpening passes you want to perform (1- Pass Sharpening, 2- Pass Sharpening or 3-Pass Sharpening). The current number of passes is checked in the menu.

If you select multi-pass sharpening, either 2 or 3 tabs are displayed at the bottom of the dialog box to let you switch between the settings for each pass. The Pass buttons at the top of the dialog box let you toggle any pass on or off which lets you see what effect it is having on the result.

Sharpen Luminance Only

This toggles the Sharpen Luminance Only setting. If the menu item is checked, just the brightness information (luminance) is sharpened, while color information (chrominance) in the input image is preserved. This can be useful, for example, when sharpening areas with color noise without amplifying the noise, but generally the difference is very subtle.

Preview

A 1:1 preview of the sharpen effect is displayed in the right-hand side of the dialog box. You can resize the preview by resizing the dialog box. Clicking on the input image re-centers the preview at the point you click. Or, you can drag within the preview area to move around the image.

If you enlarge the dialog box, you can make the sliders wider and the preview area narrower or vice versa by dragging the vertical separator line between them.

 Preview Button

Clicking the Preview button causes the full output image to be recalculated, not just the preview area. This can be useful if you want to view the entire image at once and not just a small section, but it can take longer to compute.

 Difference Button

Clicking the Difference button causes the preview to display the difference between the original image and the preview image. Differences are exaggerated by a factor of two to make them more apparent.