In this article, I’m going to talk about noise reduction and sharpening specifically how to read, interpret, and adjust the sharpening and NR tools in Lightroom and Adobe Camera RAW (ACR) in as much of a directed manner as I’ve been able to develop.
This article builds in a large part on two previous articles. First up is my article on my camera acclimation target. That target represents the best approach I currently have to figuring out how my camera will behave and how to get the most out of it in Lightroom. The second foundation piece is my article on crating Lightroom/ACR develop defaults. I use these in conjunction with my target, to get Lightroom/ACR configured to get me close to optimal right out of the box.
That said, while I use my camera acclimation target for this kind of work, there’s no reason that you have to. All of the discussion presented in this article about noise can be applied to any other test target or conditions. In fact, it can be applied to real world images too. However, if you’re setting up defaults, my experience has been that I can tune better with an artificial test target then verify my results on real images, as opposed to trying to dial things in on real images.
General Theory of Sharpening and Noise Reduction
Sharpening and noise reduction work in counter productive ways to each other.
Noise reduction works by averaging the values of adjacent pixels, fundamentally reducing the contrast between them. Sharpening, does the exact opposite, increasing the contrast between two adjacent pixels to make the edge more defined.
For the most part, at least when there’s a lot more signal than there is noise, sharpening and noise reduction don’t really step on each other’s feet so much. However, as the intensity of noise increases relative to the signal, it becomes much more difficult for both process to work well.
The point here is that getting optimal sharpening and noise reduction is a balancing act. Noise reduction, or at least too much noise reduction, can make details and edges softer, requiring more sharpening, which makes the noise elsewhere in the image more intense. Finding the right balance is the key.
With that out of the way, lets move on to how I go about setting up noise reduction and sharpening.
Step 1: Color Noise Reduction
I start my noise reduction and sharpening tuning with the color noise reduction. Of the three options — color noise, luma noise, and sharpening — color noise I find is the most independent of the others. By this I mean there’s not much of a relationship between color noise and sharpening, or vice versa. Therefore, you only have to really worry about the color noise itself and then you’re done.
Broadly, the objective here is to get rid of off colored pixels and patches of color casts in an image without creating excessive bleed across color boundaries.
Lightroom provides three sliders for adjusting color noise; color, detail, and smoothness. Adobe’s documentation on the matter has this to say:
Color : Reduces color noise.
Color Detail : Controls the color noise threshold. Higher values protect thin, detailed color edges but can result in color specking. Lower values remove color speckles but can result in color bleeding.
Sadly, the documentation on Adobe’s site doesn’t talk about the smoothness setting. But from what I can tell the effect of smoothness is to eliminate large blotches of erroneous color. It appears that this is done by expanding the range over which the algorithm makes adjustments. A higher smoothness value, means the color NR algorithm works over a wider range. The side effect of this, appears to be that at high smoothness values color values along boundaries may be distorted/averaged.
So broadly speaking, I want the color (amount) slider to be as low as possible while removing all the color noise. This insures that there isn’t excessive noise reduction being applied blurring color detail that shouldn’t be blurred. I want the detail slider as high as I can reasonably set it without getting oddly colored pixels or blotches in my image. This preserves the most color detail without having erroneous color areas. Finally, I want the smoothness slider set just high enough to remove any large scale erroneous blotches of color. This removes the most erroneous color blotches without creating excessive bleed over across color boundaries.
|Setting||Target||What to look for:|
|Color||As low as possible while still removing all or as much of the color noise as possible||Look at a neutral mid or dark gray to be free of color noise.|
|Detail||As high as possible without retaining erroneous color pixels||Look at a mid to dark gray or solid color for color pixels, look at a resolution strip to see the effect of the adjustment on detail|
|Smoothness||As low as possible while still removing blotches of color||Look at a mid tone gray for blotchiness and a boundaries between colors for bleed (over smoothing)|
Step 2: Luma Noise
With the color noise taken care of I move to dealing with the luma noise. Luma noise is very strongly coupled with sharpening, and these two setting almost have to be tweaked together to maximize the results. That said, I start with luminance noise because I find that getting it dialed in makes it easier to do the sharpening. If the noise is already well controlled, the sharpening procedure is a lot more straight forward.
Similarly to color noise, Lightroom provides 3 sliders for dealing with luminance noise; luminance, detail, and contrast. Adobe’s documentation has this to say on the matter.
Luminance Reduces luminance noise.
Luminance Detail Controls the luminance noise threshold. Useful for noisy photos. Higher values preserve more detail but can produce noisier results. Lower values produce cleaner results but also remove some detail.
Luminance Contrast Controls the luminance contrast. Useful for noisy photos. Higher values preserve contrast but can produce noisy blotches or mottling. Lower values produce smoother results but can also have less contrast.
Again the general strategy here pretty much mirrors the strategy with color noise. You want to adjust the luminance setting just high enough that the noise is controlled or removed but not so high that you start obliterating details. For the detail slider, you want to set it as high as possible without exacerbating the noise. And finally contrast, again this wants to be pushed as high as possible without creating mottling.
It’s also likely that now that you’ve started removing luminance noise, that you’ll start to see some large scale color noise splotches creep back into the image. This is expected, since the luma noise will mask some of your ability to perceive the color noise when you first did the color noise reduction pass. Remember, I said it was the least coupled, not completely decoupled. If you start seeing splotches of discoloration in a neutral color patch, go back and increase the color noise reduction slightly to clean it up. Though understand, that in some cases, especially at high ISOs, it may not be possible to clean up the color noise completely.
|Setting||Target||What to look for:|
|Luminance||As low as possible while still removing all or as much of the noise as possible||Look at a neutral mid or dark gray to minimize or be free of noise.|
|Detail||As high as possible without creating or exacerbating noise||Look at a mid to dark gray or solid color for color pixels, look at a resolution strip to see the effect of the adjustment on detail|
|Contrast||As high as possible without creating contrasty blotches||Look at a solid mid-tone color for the effect on blotches, look at the fine resolution strips to judge contrast.|
Sharpening is fundamental the opposite of noise reduction, and this and luminance noise reduction are the most tightly coupled of these settings. Sharpening will enhance the appearance of noise, and likewise, noise reduction will soften edges and remove details from the image. It’s very much a balancing act between these two settings, and the part of the process that I spend the most time going back and forth on adjusting.
Like with the previous sections, I’ll start off with what Adobe’s documentation says on the 4 sliders available.
Amount Adjusts edge definition. Increase the Amount value to increase sharpening. A value of zero (0) turns off sharpening. In general, set Amount to a lower value for cleaner images. The adjustment locates pixels that differ from surrounding pixels based on the threshold you specify and increases the pixels’ contrast by the amount you specify.
Radius Adjusts the size of the details that sharpening is applied to. Photos with very fine details may need a lower radius setting. Photos with larger details may be able to use a larger radius. Using too large a radius generally results in unnatural-looking results.
Detail Adjusts how much high-frequency information is sharpened in the image and how much the sharpening process emphasizes edges. Lower settings primarily sharpen edges to remove blurring. Higher values are useful for making the textures in the image more pronounced.
Masking Controls an edge mask. With a setting of zero (0), everything in the image receives the same amount of sharpening. With a setting of 100, sharpening is mostly restricted to those areas near the strongest edges.
With that said, there’s a lot more of a personal taste aspect involved in this. What appears over sharpened to one photographer may not appear over sharpened to another.
Also be cognizant of the display you’re working on. While Lightroom is applying the same adjustments to the images, you may or may not see them as well — you’ll certainly see them differently — when working on a high DPI display versus a standard DPI display.
Unlike noise reduction, the dance with sharpening is considerably more difficult. In part, this is because the optimal settings for sharpening depend on the subject matter, remaining noise, and even the resolving power of the lens. This differs from noise, where the camera’s sensor and ISO setting are the dominate noise considerations.
The biggest side effect of sharpening not being tied only to the camera sensor, is that there will be a level of optimization that is needed on a per image basis beyond what can be set as a default.
Broadly speaking, in my taste, I aim for a sharpening amount between 50 and 80. In almost all cases I prefer to under sharpen then over sharpen. This also presumes that Lightroom’s scale (0–150) is roughly percentage based, where 100 would equate to 100% of the sharpening algorithm’s performance.
According to Adobe, radius controls the size of the sharpening detail. In practice it seems like it’s more of a case that it controls the size of the sharpening halo (the range over which the contrast adjustments are made). For the most part I’ve always left the radius around 1 (px).
That said, I’m finding more and more that at higher ISOs, increasing the radius is highly beneficial. I suspect this is in part due to the nature noise always being pixel sized, while the details that aren’t obliterated by the noise are often larger than a single pixel.
However, radius is a setting that is worth playing around with in images. Inherently low detail images may benefit from a higher radius setting.
The detail slider is, I think, the least understood of the various sharpening sliders. Even having reading Adobe’s documentation I don’t fully internally understand it, at least not intuitively enough to understand what I should be aiming for. For the most of my history with sharpening, I’ve ended up setting it down somewhere around 35 or so. Of course this, in combination with my amount of 70, could mean that I generally under-sharpen my images. Or maybe not.
The problem, and this sadly is where the extent of my experience ends, is figuring out the right value fro radius and detail.
Masking, is the final sharpening control provided by Lightroom/ACR. Masking controls the areas where sharpening is and isn’t applied based on broader edge and detail detection algorithms. Because of this, masking is highly context sensitive — what’s acceptable on one image may not be acceptable on another. As a result of this, when setting up camera defaults, I leave masking set to 0, and apply it on a per image basis while holding the alt-key. What I’m looking for when doing this is that the edges and details remain white while solid color areas go as black as possible.
Broadly, my objective with sharpening is to do what I can to minimize the enhancement of noise while maximizing the enhancement of detail. However, especially at high ISOs, it’s often necessary to accept a level of sharpen enhanced noise.
Radius and detail are some of my last used, and as a result probably most under-utilized handles on sharpening. I suspect this is probably true for a lot of other Lightroom/ACR users, and that there’s probably some gains that can be made in image quality figuring out just how to use this to your advantage.
|Setting||Target||What to look for:|
|Amount||Highest possible value that doesn’t cause over sharpening||Look for exaggeration of noise and over sharpening|
|Radius||Varies depending on the material in the image, ISO, lens resolution, and diffraction|
|Detail||Varies with image content|
|Masking||Varies with image content||In the alt view, smooth color areas being black, edges and details highlighted as white|
Shadow Tint Color
The final optimization that may need to be made, though typically only at the very highest ISOs is to look at the shadow tint color.
The color filters in the sensor don’t just perfectly filter colors, they also absorb some of the light itself. The camera compensates for this by driving each of the colors with a different amount of amplification or gain, to insure that white stays white. Think of this like ISO, but the ISO in this case is specific to the color.
The side effect of having different gains on the each colors, is that at high ISOs, when there’s already a lot of gain and very little signal, the noise characteristics of the individual colors will be different. This is especially true in the shadows at high ISOs where there’s an even lower sign to noise ration. The result of this is that shadows can take on a color cast.
Lightroom allows for correcting these shadow tints across the green/magenta axis. Since most cameras have much less optically transmissive blue and red filters, compared to the green ones, this is generally the axis that the cast will show up with.
For example, on my 5D mark III, at the highest ISOs, I need to remove magenta (or add green depending on how you look at it). But only at ISO 102,400.
The shadow color adjustment is found in the Camera Correction tab, and offers a range from green to magenta. In my experience with Canon cameras, at the highest ISOs I’ll need to adjust the shadows towards green to compensate for the lower transmittance of the red and blue filters.
I hope this helps shed some light on the thought process and what to look for when it comes to noise reduction and sharpening. I would hasten to point out though, that my method is not the only method that can be used. Some settings, especially sharpening, are also highly dependent on the subject matter too. Finally, I want to reiterate my point that it’s very useful to have a controlled test image to setup baselines that you can refine and tune to get the most out of your actual images. I spent a lot of time stabbing in the dark trying to workout good settings on actual images, and never got close the quality I’m getting now having started with controlled test images.