DPP Home Technique (R)evolution Blur Color Noise In Photoshop

Tuesday, April 6, 2010

Blur Color Noise In Photoshop

Try this simple but powerful technique to make a cleaner-looking image

This Article Features Photo Zoom

1) Background with noise
When you have noise in an image, there’s a lot you can do about it. There are many ways you can reduce noise during postprocessing; you could even say there’s an art to it. Learning these techniques can improve good exposures and save others.

2) Blurred color layer
First, take steps to reduce noise at the point of capture. Favor low ISOs and avoid very long exposures. Next, use RAW-conversion software to reduce moderate amounts of noise. Finally, use Photoshop and third-party noise-reduction software for aggressive amounts of noise. The KISS principle applies. Use simple methods if they provide good results. Use progressively more powerful and sophisticated tools only as challenges arise.

3) Color Blend Mode blurs color only
In the January/February issue of DPP, I showed you how to reduce noise with the Photoshop filters Despeckle, Dust & Scratches, Median and Reduce Noise, and in the March/April issue, I showed you how to reduce noise using Adobe Camera Raw and Lightroom (an updated version of the March/April Revolution column will be available at the DPP website when you read this). In this column, I’ll show you how to reduce noise in Photoshop using a simple technique to blur the color noise and therefore dramatically reduce its prominence in the image.

4) The layer stack
On the one hand, it’s difficult to reduce luminance (light and dark) noise without compromising image sharpness; often, it requires careful application of specialized software. On the other hand, color-noise reduction is comparatively easy and has less severe side effects—typically, slight reductions in saturation, particularly along contours. You easily can reduce most chrominance (hue and saturation) noise using Photoshop.

5) Noise in image
1. Duplicate the Background layer and turn the new layer’s Blend Mode to Color.

2. Blur the layer (Filter > Blur > Gaussian Blur).

Examine images at 100% magnification while you’re determining settings to apply. Only this screen magnification will accurately display granular detail.

Using this technique, only the color of an image is blurred, not its luminance, so image sharpness won’t be compromised. Be careful not to use the blur filter too aggressively. This may result in contours with reduced saturation and possibly fields of color with lower saturation and hue variety. If you can’t go far enough without encountering these side effects or if larger blocks of color noise persist (possibly from Bayer pattern demosaicing or JPEG artifacting), then use third-party software for noise reduction.

6) Color noise reduced
(note luminance noise persists)

7) Color noise reduced too aggressively (contours desaturated)

8) Color noise reduced too aggressively (saturation reduced overall)

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


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