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Removing Grain using Photoshop

Nick Evans , Jan 12, 2005; 08:24 a.m.

Hi

I have several scanned images and some of them have noticable grain in the sky or older images have grain across the image.

So using Photoshop how do you go about reducing or removing the grain from the images?

TIA

Nick

Responses

Beau Hooker , Jan 12, 2005; 08:36 a.m.

Hi Nick, I think the *best* way is to download a copy of NeatImage or Noise Ninja - I believe they have evaluation copies. They can do truly amazing things. If you want to stick with Photoshop, here are a couple of suggestions:

1) Identify the channel that has the most noise and either use gaussian blur or one of the noise filters (like dust and scratches) to blur that one channel. Many times the noisest channel is the blue channel, but not always. This is usually preferable to blurring all three channels

2) I've had mixed results with this method but you can try it: Convert your image to Lab Color Mode (Image>Convert to profile>Lab Color) Apply a gaussian blur to the A and B channels (try 1.5 pixels to start) Be sure to leave the Luminosity channel alone. Convert back to RGB.

Again, nothing that I'm aware of in Photoshop can touch NeatImage. Give it a look. Good luck!

Jean-Baptiste Queru , Jan 12, 2005; 11:50 a.m.

Typically, I'll select the areas of plain color on which I want to reduce grain, with some margins around (reduce selection by a few pixels), then apply a 2-pixel median filter followed by a small gaussian blur.

On the whole image, a 1-pixel median filter is usually enough for my taste.

Those aren't advanced tools, though, and they are probably not able to provide results as good as specialized solutions.

Steve Dunn , Jan 12, 2005; 02:13 p.m.

It may depend on what version of Photoshop you're using.

In my old copy of Photoshop LE 4.0, I used to use despeckle (sometimes multiple times on backgrounds, but no more than once on the subject since it tends to remove actual details as well as noise) and, for backgrounds that should be blurry, Gaussian blur. I was never truly happy with the results.

Photoshop Elements 3.0 has a noise removal tool built in. It's not perfect, and I'm sure Noise Ninja et al. do a better job, but at least Elements' tool is configurable, unlike the despeckle tool. So far, I've only used it on film scans (2720 dpi) from 400UC and NPH, but I've been reasonably pleased with the results. And I can still use despeckle and/or Gaussian blur as needed.

I don't know for sure but I wouldn't be at all surprised if recent versions of the full Photoshop product include the noise removal tool as well. If your version of Photoshop has this tool, give it a shot and see how it works; you've already paid for it and it may do the job. If you're not happy, or if you want to try out the competition, Noise Ninja et al. have free trials you can download from their Web sites so you can determine if they're worth the money for your particular application.

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