Noise Reduction and Magnification
Submitted by mitch on Sun, 06/29/2008 - 00:37.
I was chatting with George Bowen by e-mail this week. He's a consultant for Imagenomic, the manufacturer of Noiseware.
The timing was perfect, because I also got into a minor dispute over noise reduction settings this week in one of the forums on Luminous Landscape. Someone posted a couple of magnified crops from a photograph to argue one technique for noise reduction was better than another. I threw a clinker into the discussion when I complained that the magnified samples settled nothing. Who cares about noise magnified to the size of aquarium gravel? What matters is the appearance of noise at print size.
Two arguments were tossed back at me:
- using high magnification helps to identify noise and choose settings to remove it, and
- it's best to do noise reduction at high magnification to create a master that can be used to make prints at different sizes.
Whether your editing software calls it 100% Zoom or Actual Pixels, what you see on your monitor at that zoom is a grossly magnified view of what will end up in print.
Gurus who write books and give seminars will blow up photos to point out noise. There's nothing wrong with a quick zoom to identify noisy areas to watch. Once your mapped those areas in your mind, however, you need to pull back on the zoom.
Magnified views distort our perception of noise. They're guaranteed to scare you. You see pixel-level abnormalities on the monitor that would require a loupe to see on a print and that would be invisible to the eye at normal viewing distance.
You will almost certainly reduce noise too much by using higher magnification as your guide. The result is the obliteration of fine details in your photograph that could be preserved with proper technique. You'll grow old trying to eliminate every visible artifact at high magnification, too.
There also is no "one setting fits all zooms" for noise reduction. The idea of creating one master file and then resampling it for prints at different sizes is attractive. It saves time. Unfortunately, it just doesn't work well with noise reduction. The relationship between the visible appearance of noise and image features is not fixed.
You can prove this to yourself by taking any noisy photograph and temporarily reducing it to 25%. Lots of visible noise will disappear or become less obvious. George said it well. "Pixel peeping at anything other than intended output size is a waste of time . . ."
Optimal noise reduction is just enough to make noise non-obvious. Any more than that risks loss of important detail. Stated differently, noise reduction settings for the same photograph will vary for different print sizes. Don't do your noise reduction at high magnification and then expect it to look better at lower magnification. That's not going to happen except in the luckiest of circumstances. You just end up throwing away detail.
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Noise reductioin
Mitch,
Thanks for the comments on noise reduction. I agree - in a lot of cases overusing noise reduction will reduce sharpness and for no extra gain in the printed version of the photograph. I do like to "pixel peep" prior to noise reduction but only to get a feel for the type of noise - luminance vs. color. That helps me decide on the noise reduction to be applied in Lightroom.
If I have a noisy photograph (high ISO, low-level exposure or ...) I will usually apply some level of noise reduction in my raw processing using LR. That will often be enough and I really try to minimize the loss of detail. If needed I will then use NoiseNinja in PS. I haven't done a real comparison of noise reduction plug-ins but I'm pretty happy with NN to date.
Do you have any comments on this workflow especially regarding the initial noise reduction step in raw processing?
Thanks,
Ernie
EA Fotos
Noise Reduction
Thanks for the reply, Ernie.
It's OK to pixel peep to get a feel for the amount of noise and the nature of the noise. If you need to magnify the photo to clearly see evidence of noise, you should not have a severe problem with noise at typical enlargements. IOW, if noise is not noticeable without magnification, you might not need any noise reduction (or, if you do, it will likely be slight).
My comment is aimed at removing visible evidence of noise while viewing a greatly magnified version of the photo on a monitor. You will very likely apply too much noise reduction and end up softening the photo.
The sharpening and noise reduction abilites of ACR continue to improve. It is now possible to effectively presharpen photos with LR or Camera RAW.
If you find that LR can effectively remove noise, I'd use that solution. I would avoid applying noise reduction and/or shaprening in LR and then using Noise Ninja in Photoshop on the same photo.
NN is a very effective tool. I am working on a very comprehensive review of Noise Reduction tools: Akvis Noise Buster, Nik Dfine 2.1, Neat Image, Noise Ninja, Noiseware, Picture Cooler, Power Retouche Noise Filter, and Topaz Adjust. Plus I'll be including Adobe LightRoom, Camera RAW, and the Photoshop Reduce Noise filter.
I'll have more than a little to say about noise reduction workflow as part of the noise reduction comparison.
I can say this much. All of the tools I mentioned -- including Noise Ninja -- do an effective job of noise reduction. There is no consistent winner that outperforms the others on any image. Also, no consistent loser. There are big differences in their user interfaces, tools for diagnosing noise, and the ability to selectively remove noise and/or preserve details. They also vary in the support for Smart Filters in Photoshop CS3/CS4.
You can do an effective job of noise reduction with any of these tools by applying them to a layer so you can adjust the layer opacity and use a layer mask to adjust their effects as you retouch the image.
Cheers,
Mitch
Magnification and NR with Nik Dfine 2.0
Mitch,
I have really enjoyed your writings on Noise Reduction, and have learned a lot. based on your reviews, I have purchased Nik Dfine 2.0, and am very pleased with my purchase -- it fits my needs perfectly.
I've been reading some of your other posts on forums and ran across this blog post. Since Dfine can automatically apply noise reduction in a batch file (I use droplets), what is the implied magnification level that the software uses in the auto process. If it may be too strong, is there a way to moderate it with an auto batch process?
Thanks,
Nick
Re. Magnification and NR with Nik Dfine 2.0
I'm glad the review was helpful you, and you're comfortable with your decision. :)
The issue with zoom magnification is seeing evidence of noise that's not at all apparent at print size. It's an issue when you are working with Dfine on a single image.
Nik Dfine will use a custom profile for your camera and ISO, if you've downloaded one or made one yourself. I suggest you have a custom profile, if you're going to use Nik Dfine in batch mode.
I recommend two settings:
(1) Auto Profile Load Behavior = Load Based on EXIF Data
(2) After clicking OK = Apply the filtered effect to a separate layer
With Nik Dfine 2 applied to a separate layer, you can adjust layer opacity to reduce the effect.
Cheers,
Mitch