Reducing Luminance "Noise" In Blue Skies

What is the best method of removing luminance "noise" in large expanses of blue sky? And at what stage of the workflow should this be performed?

I used ACR 5.6 to remove as much as I could, but still find my sky to be "noisy" or "grainy" looking. ISO is 400, that maybe contributing some noise to the image, but the rest of the image looks pretty clean.

TIA

Use a selective sharpening method. Sharpening noise will make it more visible.

I use ACR (CS4) to remove some of the luminance noise. If the shot is noisy in Photoshop I use either Neat Image noise reduction or Power Retouche. If it's a landscape with a lot of sky I will just select the land area to sharpen, and leave the sky unsharpened.

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Originally Posted by Terry Tedor

What is the best method of removing luminance "noise" in large expanses of blue sky?

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Just select it and then use a Gaussean blur :)

In "desperate times" just replace it with a graduated fill. :eek:

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Originally Posted by Terry Tedor

What is the best method of removing luminance "noise" in large expanses of blue sky? And at what stage of the workflow should this be performed?

I used ACR 5.6 to remove as much as I could, but still find my sky to be "noisy" or "grainy" looking. ISO is 400, that maybe contributing some noise to the image, but the rest of the image looks pretty clean.

TIA

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Hi Terry,

I use the ACR NR "to the max" (both 100) all the time (no one complains) and I'd certainly expect that to remove it for you at 400 iso unless you;
a) had under-exposed and brought it up significantly with exposure, brightness, etc., and/or
b) had the wrong WB set (e.g. tungsten) and had to make a huge correction, and/or
c) have a very noisy camera

Not that I'm accusing you of these heanous (sp?) crimes - just suggesting what might be causing the problem ;)

Any images I have where ACR's NR is insufficient (e.g. > 1000 iso), I treat with Neat Image as Rob does.

Hope that helps,

Thanks all for the inputs. If I decide to go the route of Gaussean Blur or use the Dust & Scratches filter, were in the workflow is it best to do that?

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Originally Posted by Terry Tedor

Thanks all for the inputs. If I decide to go the route of Gaussean Blur or use the Dust & Scratches filter, were in the workflow is it best to do that?

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Fairly early I would say.

You can get a free trial of Neat Image and it works standalone if your image editor isn't one of the many it supports as a plug-in.

If you do try Neat Image, always do it before cropping.
Here's a link to my 5 click workflow, it (almost) couldn't be simpler!

Cheers,

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Originally Posted by Terry Tedor

Thanks all for the inputs. If I decide to go the route of Gaussean Blur or use the Dust & Scratches filter, were in the workflow is it best to do that?

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Dust and Scratches can work quite well at 1 pixel - but beyond that it starts to soften the image quite noticeably.

Also be aware that when you're making a select for a Gaussean blur, it doesn't need to be overly precise; if there are a few noise pixels creeping in between boundries it's not generally noticeable at anything other than 100% magnification.

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Originally Posted by Dave Humphries

Fairly early I would say.

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Yes, I thought so too. Should I pass on using ACR to perform Capture Sharpening to avoid sharpening the noise too and instead, go with Colin's prefered method of Capture Sharpening as one of the first steps in CS4, but AFTER any noise reduction?

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Originally Posted by Dave Humphries

You can get a free trial of Neat Image and it works standalone if your image editor isn't one of the many it supports as a plug-in.

If you do try Neat Image, always do it before cropping.
Here's a link to my 5 click workflow, it (almost) couldn't be simpler!

Cheers,

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Do you know how Neat Image compares to Topaz Labs' DeNoise? I did some comparisons between DeNoise, Noise Ninja, and Dfine and found DeNoise ran circles around the other two at removing/reducing chrominance noise. I never thought to use a third party plug-in to remove luminance noise, thinking they were designed specifically to remove chrominance noise in high ISO images.

Thanks for the link to the other thread. I will be sure to give that a try if I decide to test drive Neat Image.

For what it's worth Terry, the single thing that ACR just "doesn't do for me" is capture sharpening ... Canon recommend 250% or 300% (depending on which white paper you read) @ 0.3 radius - and ACR just won't go that low. I usually do capture sharpening right after dust bunny removal, but than again, I don't normally have excess noise to deal with. If you DO have noise then probably just as easy to apply capture sharpening to the entire image and then just use the history brush to roll it back over the noisy areas (capture sharpening does very little to the image at normal print & display sizes anyway - it just makes it nicer to work on at higher magnifications).

Thanks Colin. Yes, I remember what you wrote in the sharpening thread. Wouldn't it be easier to deal with the noise reduction first, and then apply the capture sharpen?

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Originally Posted by Terry Tedor

Wouldn't it be easier to deal with the noise reduction first, and then apply the capture sharpen?

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Sharpening and noise reduction work against each other - so if you apply noise reduction first then your capture sharpening may not be as effective, and vise versa :)

Hi Terry,

I also agree 200% with Colin on not using ACR for any sharpening.

I find the ACR's NR does not unduly harm fine detail, at least, nothing that capture sharpening cannot put back.

I have no experience of any other noise removal tool I'm afraid - I don't need to, I have something that works for me :)

The thing that makes Neat Image special (I cannot claim unique, because it may not be), is that it samples and area of no detail in the image, like a blank bit of sky, determines the type of noise, replicates it and subtracts it from the whole image - you have control over the amount of subtraction in both luminance and colour. This is why, unlike a standard filter low pass stye filter, or a gaussian blur, does not damage fine detail (much).

My workflow, for noisy images is:
Open in ACR, process RAW including, on Details tab; no sharpening, 100 on both Noise channels.
Open in PS Elements, use Neat Image, then capture sharpen, process more as necessary (cloning etc.), if for web use; reduce image size, output sharpen, then save.

In fact for really noisy images, like these, I sometimes skip the capture sharpening altogether and rely solely on output sharpening after any size reduction, it gives a cleaner result, as the downsize also reduces noise (and fine detail if there were any there).

Cheers,

Well, they certainly don't look at all noisy to me. Nice shots, BTW.

Colin and Dave - Thank you both for your help, I really appreciate it. It's given me the direction I needed.

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Originally Posted by Terry Tedor

I used ACR 5.6

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A very good way to avoid noise in the first place is not to use ACR - it is well accepted that in its current incarnation ACR conversions are inherently noisy, simply because of the the demosaicing algorithm it uses.

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Originally Posted by Keith Reeder

A very good way to avoid noise in the first place is not to use ACR - it is well accepted that in its current incarnation ACR conversions are inherently noisy, simply because of the the demosaicing algorithm it uses.

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Unfortunately, Adobe just can't win ... when they ramped up the noise reduction in v4.1 people started complaining that the images were "too soft" so they toned it down in v4.2 thus making images "noisier". In the current incarnation you have good control via the built-in noise reduction sliders to tailor the conversion.