After you have loaded or created a profile, you are ready to remove noise from the image. First, activate the Noise Filter:
There are two sets of filter controls, the "Standard" settings, and the "Color-selective" settings. The Standard filter settings apply to the entire image. The Color-selective settings are used to adjust filtering for specific colors, which is occasionally useful for grass or other textured areas of a single color.
Tip: Zoom to 100% magnification when you are working with the filter tool. This will make it easier to see both the noise and the effects of noise reduction when you are adjusting the filter settings.
If you don't see the green preview rectangle, click anywhere in the image to display it and position it. (The Noise Filter tool must be active in order for it to be displayed.)
The preview rectangle shows the effects of the current filter settings. When you make adjustments to the settings, the preview rectangle is updated. If you have a slow machine, you might want to choose a smaller preview size in the Preferences dialog, so the preview will be updated more quickly.
You can turn off the preview by right-clicking or control-clicking in the image, or by toggling the Preview button:
The individual filter controls are described below. Usually, if the current noise profile is matched correctly to the image, the default settings will yield reasonable results. In any event, after the settings are adjusted to your liking, hit the remove noise button to filter the entire image:
After you filter the image, you can use the Before button to toggle between the unfiltered and filtered image:
Press and hold the button to view the unfiltered image. If you want to go back and refilter with different settings, you can go to the Edit menu and choose Undo, and the unfiltered image will be restored.
The Standard filter page includes three groups of controls. The luminance group affects filtering of noise in the brightness component of an image. This is usually the part of the image that contains the most real information. The colors group controls filtering of color noise, which is often the most displeasing noise. The sharpness group enhances edge sharpness using an unsharp mask.
Strength controls how aggressively the filter is applied. This is the control that you'll normally want to adjust if you don't like what you see in the preview rectangle. If you move it far to the right, the image may look too plastic-like. If you move it to the left, it will look more grainy. Often the most natural-looking results are achieved when you leave a modest amount of grain. The human eye tolerates a certain amount of noise when it is accompanied by detail, and the luminance channel contains most of the detail in an image.
Smoothness increases or decreases the noise levels estimated by the Noise Profile. Usually the default setting is adequate, but if you see isolated specks in smooth areas, try increasing the smoothness setting to see if they go away. (Here's a tip for adjusting the Smoothness slider: Move the preview window to a smooth background areas, and move the Strength slider all the way to the right so the preview is a smooth as possible. Then set the Smoothness slider to the minimum level such that the preview is still smooth (if it is too low, you will usually see isolated specks). Finally, lower the Strength slider until you like the results.)
Contrast and saturation apply a scaling factor to edges, similar to an unsharp mask, but at several resolutions simultaneously. You probably won't need to adjust these in most situations.
Sharpness amount and sharpness radius apply a conventional unsharp mask to the filtered image. Some people prefer to set the amount to zero and do sharpening later in the workflow. However, even in that case, it can be useful to preview the sharpening effect to see how it interacts with the noise reduction. The Suppress halos option eliminates unnatural highlight artifacts that can occur when high sharpening levels are used
In addition, there are some controls at the top of the panel. Filter coarse noise is occasionally useful when an image has very low-frequency noise, usually in the color channels. Turbo mode takes a few shortcuts to accelerate filtering. Usually the difference in quality is negligible, but sometimes strong diagonal edges may show some aliasing artifacts ("jaggies").
Here is a quick and easy strategy that often yields excellent results:
The color-specific filter allows you to increase or decrease filter strength for particular colors. This can be useful for images with green turf, blue sky, or other color areas where you want to modify filtering selectively. [See also the description of the Noise Brush, which is sometimes an easier way to selectively modify the filter.]
To use the color filter, click on the eyedropper button:
Next, click on one or more pixels in the image. The eyedropper averages a 3x3 region. Each time you select a pixel, the correponding color will be highlighted in the color grid. Move the slider to increase or decrease filtering for that color. The preview window will be updated to show the effect. (Toggle the eyedropper button off to move the preview rectangle.)
You might need to make several selections close together in order to cover the intended color range adequately. Also, try to avoid making significantly different adjustments to similar colors, as this may lead to unexpected artifacts when nearby pixels that are close in color are pulled in opposite directions.
You can save filter settings directly to a file by clicking on the "Save Settings" button:
You can also embed filter settings in the current noise profile by clicking on the "Save to Profile" button:
Next time you load the profile, the settings will be loaded along with it. This allows you to create a profile and tune the settings for a particular camera and reuse them on subsequent images with little or no adjustment required -- just load the image, load the profile, and hit the "Remove Noise" button.
A useful tool called the Noise Brush is available for fine-tuning noise reduction results. Click here for details.
