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Tuesday, December 15, 2009

Reduce Noise With Photoshop Filters

Despeckle, Dust & Scratches, Median and Reduce Noise are all tools that are built into Photoshop, and they may be the only tools you need

This Article Features Photo Zoom

Dust & Scratches Dialog Box

Dust & Scratches. It’s classically used to reduce the amount of retouching needed by images as it removes small artifacts, like dust and scratches, but it also can be useful for modest amounts of noise reduction. There are two sliders. Radius controls the amount of blurring; higher Radius settings subdue more noise and may compromise detail. Threshold restricts the number of tone levels the filter is applied to, making the filter selective with respect to luminosity values; very high Threshold settings may introduce sharp transitions in texture between blurred and unblurred areas. Used aggressively, this filter will subdue small textural detail and compromise image sharpness. Used carefully, this filter can effectively reduce modest amounts of noise.

Reduce Noise. Offering the most control of the Photoshop filters, it can deal with moderate amounts of noise relatively well. Strength controls the intensity of the filter. It’s the blurring effect. Preserve Details reduces the effect of the filter initially targeting contours and later by targeting higher and higher detail frequencies or image texture. The settings you use are entirely dependent on Strength settings and image content. Higher frequency detail merits higher settings. It’s not a panacea. High Strength and Preserve Detail settings can make some areas of an image look synthetically smooth and yet still fail to remove small artifacts, especially near contours. Reduce Color Noise blurs color without affecting luminosity. You can be relatively aggressive with this slider, but if you use it this way, guard against reduced saturation, especially along dramatic contours. Sharpen Details attempts to restore image sharpness after blurring. Use it conservatively. More sophisticated sharpening can be performed with other filters in Photoshop. Remove JPEG Artifact is somewhat effective for reducing JPEG compression artifacts, such as blocky color and jagged edges. Use this check box only on JPEGs that contain artifacts. (Don’t use it on TIFFs from RAW files.) If you can’t remove all of the JPEG artifacting in a file without compromising image quality, turn to third-party plug-ins. Although it’s the most advanced Photoshop filter for noise reduction, like all the others, when used for major noise reduction, it may compromise image sharpness.

Reduce Noise Dialog Box

Using These Tools. Use these tools when you can’t adequately reduce noise during RAW conversion and you only need to go a little further. For many images, they may be all you need. None of these tools is up to the task of industrial-strength noise reduction. Applied too frequently or too aggressively, they will compromise image sharpness unnecessarily. For aggressive noise reduction, turn to third-party software.

Whenever you blur an image to reduce noise, don’t overdo it. Blur enough to reduce noise, but no more. If you go too far with blurring effects, you’ll spend a lot more time trying to restore image sharpness and may never achieve optimum results. Just as there are limits to how much apparent sharpness you can restore to a poorly focused image, there are limits to how much more apparent sharpness you can reintroduce after blurring. Use a light touch. Sometimes the noise is more desirable than reduced sharpness. Sometimes the presence of noise is even desirable; it can keep images from seeming synthetic and even make some images appear slightly sharper.

John Paul Caponigro, author of Adobe Photoshop Master Class and the DVD series R/Evolution, is an internationally renowned fine artist and authority on digital printing. Get over 100 free downloads and his e-newsletter Insights free at www.johnpaulcaponigro.com.