150. Blur an Image to Remove Noise Before You Begin  148 About Sharpness
See Also 149 Sharpen an Image 151 Blur a Background to Create Depth of Field 152 Create a Spin Effect 153 Soften Selected Details 154 Add Motion to an Image
If you have a grainy-looking image such as an old photograph you scanned in, you can blur portions of it to remove the graininess. Because graininess can contribute to a lack of sharpness in an image, blurring the graininess has the effect of sharpening the image. If you blur only the background of the image, you appear to sharpen the subject of the image. Keep in mind, you are creating the perception of sharpening the subject of the image by blurring the surrounding background. When you blur an image or portion of the image, the pixels along color edges are blended with one anothersometimes using averagingto create a softer edge. This averaging and blending of colors creates smoother transitions between different colored sections of the image, thus eliminating the appearance of tiny spots, often called noise, from the image. With the Blur filter, noise is eliminated from the photo by averaging the color values of the pixels where transitions occur to create hard lines or shaded areas. The Blur More filter performs the same steps as the Blur filter, but the effect is much stronger. The most versatile filter for removing noise is Smart Blur because it enables you to control how the image is blurred. The Smart Blur dialog box enables you to specify custom Radius and Threshold settings. By specifying a Radius value, you indicate how far to search for pixels that don't match. You indicate the Threshold value to specify how different the pixels must be before they are blurred. This filter also enables you to select the blur quality and indicate the blur mode. 1. | Select the Smart Blur Filter
Open the image you want to adjust in the Editor in Standard Edit mode and save it in Photoshop (*.psd) format. If it's not already showing, display the Layers palette by selecting Window, Layers. In the Layers palette, click the layer you want to sharpen by blurring the graininess and select Filter, Blur, Smart Blur.
NOTE  | To see an example of using the Gaussian Blur filter to blur a portion of a photospecifically, a portion moved onto its own layer to protect itsee 142 Fix a Flash That's Too Close. |
To limit your changes to a specific region of the image, use one or more selection tools from the Toolbox to draw a marquee around that region, protecting areas outside that region from being blurred. See 70 About Making Selections for more about making selections.
 | 2. | Specify Settings
In the Smart Blur dialog box, specify the settings for blurring your image. You can view a sample of how the image will be blurred in the preview window at the top of the dialog box.
In the Radius field, specify a value that indicates the number of pixels around each pixel that the Smart Blur filter will search for dissimilar pixels to blur.
TIPS  | Use the and + buttons to adjust the zoom size of the preview window. As you point to the preview, the mouse pointer becomes the Hand tool. Use this tool to drag the image to see another portion. Click and hold the preview window to toggle the effect off, and release to turn it back on. This enables you to compare the look of the image before and after the effect is applied. |
In the Threshold field, specify a value between 0 and 100 that indicates, relatively, how different the pixels must be in tonal difference before they are blurred. The higher the Threshold level, the more pixels are blurred in your image.
In the Quality drop-down list box, specify the desired blur quality for the image. You can select from Low, Medium, or High quality. The higher the quality setting, the longer it takes to apply the filter, although a Quality setting of High produces the smoothest results. However, the higher the Quality setting, the more likely you will have banding when you print or view the image.
The Mode list box presents the different modes the filter uses to create the blur. The default selection, Normal, blurs the entire selection. Select Edge Only if you want to create pure white edges on a pure black background, like sketches made with a thin stylus on a blackboard. Select Overlay Edge to combine this white edge with the existing image contents for a special effect that divides contrasting regions of the image by a thin white boundary.
TIPS | You can combine the Smart Blur effect with the edge mask technique discussed in 149 Sharpen an Image. To accomplish this, apply the Smart Blur to the Background layer after creating your Sharpen layer. Then create a mask layer and paint a mask for the portions of the blurred layer that you want visible. To blur a small area, you can select the Blur tool from the Toolbox. With the tool selected, specify the desired brush type and brush size. Set the Strength to 100% on the Options bar to create the most blur. Click and drag across the area you want to blur. See 153 Soften Selected Details for more information on setting the options for the Blur tool. |
When the preview appears as you intend, click OK.
| 3. | View the Result
When you're satisfied with the result, make any other changes you want and save the PSD file. Then resave the result in JPEG or TIFF format, leaving your PSD image with its layers intact so that you can return at a later time to make changes or additions.
This example features a digital photo of a ballet curtain call that suffers from many of the same problems faced by digital video photographers: It was taken at high digital zoom, using no tripod. So, the shakiness of the photographer's hand (mine), coupled with the artifacts created by the digital zoom, resulted in a nice moment compounded by the problems of modern technology.
Neither sharpening nor blurring restores focus to an image, but it can restore some sense of composition…or, at least, cover up some of my mistakes. This example actually shows two types of blurs at work: Along the edge of the photo, I used the Elliptical Selection tool to create a feathered, vignette-shaped selection, copied that selection to a new layer, and then applied a mild Gaussian Blur (see 151 Blur a Background to Create Depth of Field). For the Background layer, I used the Smart Blur filter described here. I set Radius to a low value of 3.5 to preserve the shading of Katerina's face and to prevent posterization. I then set Threshold to 15.8, which was a nice balance between blurring and losing her face altogether (higher) and returning to the original spottiness (lower).
The result shows how Smart Blur reconstructed an even tone to the subject of the image, thus restoring the illusion of sharpness; the Gaussian Blur technique compounded the illusion by taking the viewer's focus away from the edges and corners, without disrespecting the other fine performers in the production.
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