Proper Noise Reduction in Lightroom and ACR

One thing I've been noticing is that a lot of folk don't know how to optimally use the controls in the Adobe raw converters. With the smaller sensors of the mirrorless cameras, you need to understand the sharpening and noise reduction aspects of these converters in order to get the best quality conversion. 

What follows is a quick and dirty rundown on how I do that. We're going to use an ISO 800 image from the Olympus E-P2 as our guinea pig today. This image is a bit underexposed as shot, so should have some significant noise when we bring it up:

INT AF 2010 EP2 04440


Step 1: Adobe converters are generally a left-to-right, top-to-bottom process. In ACR, for example, start with the left tab (Basic) and work your way right through the tabs to the right. On the Basic tab, start with the top control (White Balance) and work your way down. If you break this sequence (e.g. use right-to-left or bottom-to-top) there's a good chance that you'll get less than optimal rendering, as you'll be changing details before you got the big picture things right. Thus, our first step is to get White Balance and the exposure-related settings right on the Basic tab before moving on. If contrast is an issue that needs to be addressed, you may have to move onto the Tone Curve tab next (though read through to the end of the article before you commit to that ;~). 

At the end of this process on the Basic and Tone Curve tabs, you should have a histogram that shows no blowouts and no blackouts, with a good distribution for the subject matter:

sharpening1


Step 2: We're ready to to deal with the edges (sharpening) and noise. Select the Detail tab. We're going to work top-to-bottom here, too, so the first thing I want you to do is kill the Adobe presets, in particular, the Color setting under Noise Reduction. We're now looking at our image pixels without any detail management. Warning: at high ISO values with the mirrorless cameras, that's going to look pretty poor. Don't worry, we're going to fix that. But first, select 100% in the scaling pop-up so that we know that we're looking at the actual pixels. Here's what Adobe's defaults look like:

sharpening2

The initial results don't look terrible, but they're soft because there's little sharpening applied. When we apply sharpening we'll get that noise showing up. Let's zero things out as I suggest so we have apples-to-apples comparisons for the next steps:

sharpening5


Step 3: Let's deal with sharpening first. Move the Amount slider up. I like to start with 100 in the Adobe converters, though I'll dial this up or down later once I've seen the full impact of my changes. Hold down the Option key (Mac) and slide Radius upward until you just begin to see some decent contrast in the monochrome presentation. That's often going to be just below or at 1.0. We're widening the impact of the sharpening on edges here, so don't go too far. Hold down the Option key (Mac) and slide Detail upwards the same way. Again, we don't want lots of contrast in the monochrome presentation, just the hint of it. That's often going to be values below 20, maybe even below 10. Finally, we're going to hold the Option key (Mac) down again and slide the Masking slider upwards. Here we're telling the sharpening engine what's a tonal area and what's detail, so we want to bring this slider up so that we're sure that areas that aren't detail are black. At this point you'll have a fairly sharp but noisy image:

sharpening3

You can see the noise more easily now, and there are hints of color noise, as well.


Step 4: Let's deal with the noise: pull up the Luminance slider until the noise disappears and then back it off just a bit. Adjust the Luminance Detail slider to preference. This is where things get a little dicey, as technically using much Luminance Detail (or Color Detail later) has a tendency to interact quite a bit with the sharpening we set. Still, it's worth seeing how far you can push the Detail sliders; later you may push them up a bit and dial down the sharpening Amount. Finally, if there's any of that red/blue/green color noise left in the image pixels, dial up the Color slider until it just disappears. What we're trying to avoid are two things: too much noise in the underlying pixels (some is okay, as long as it is not color noise), and sharpening impacts at edges that produce halos or boost contrast at the edges so much that the effect is visible.

sharpening4

You'll note that there's still a hint of noise here and my edges aren't razor sharp. I've also backed off Radius and Detail slightly in the Sharpening section after seeing how that interplayed with the noise reduction. What we're trying to do is balance settings in the conversion to get the best resulting pixels for further work. I actually tend to pick less sharpening at this stage than you might expect, as, like most pros, I use three kinds of sharpening: acquisition (what we just did), creative (what I do in Photoshop, often with layers and blending and using micro contrast adjustments), and output (what you do once you know what the output format will be). 

  • Tip: Once you figure the Detail settings out for any given camera and ISO value, you'll want to save those: pick Save Settings (in the tab name bar in ACR), select as a subset Detail, then save these under a name like EP2_ISO800. Next time you convert an EP-2 image at ISO 800 you can just Load Settings and (usually) be done. Still, if you load settings like this, always do a 100% evaluation to double-check. 

Go back and look at the original image at the top. Doesn't look noisy or unsharp, does it? (Yes, it has some additional contrast to it, which I shaped using Nik Color Efex 4.0 (another story for another day). This is one of the keys to successful conversion: don't try to do it all at once. Instead, get a good base rendering of the pixels as free from artifacts as possible, and then shape it with downstream tools. If you try to use products like Color Efex on badly converted pixels, you'll be fighting to do what you want. If you start from relatively clean pixels, you have much more latitude in what you can do. I like flat, neutral, color-accurate, artifact-free conversions. From there, I layer in my darkroom (or lightroom ;~) magic.

Don't get greedy at the conversion stage. You can boost sharpness and throw out noise and get very plastic-looking detail. I'm just under the verge of that with this conversion, so I have more flexibility with my downstream conversions. A tiny bit of noise at the pixel level is preferable to completely destroyed edge definition. Always.

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