Noise Reduction in Lightroom CC

Stonewall Farm Barn, Noise reduced, Canon G11, Small Sensor

Last week I discussed sharpening in Lightroom CC.  It seems logical that this week I travel down the “Detail” workflow to the next set of tools controlling noise reduction.  Actually, I think that Adobe should have placed noise reduction above sharpening.  In my work-flow, I typically sharpen only after I have taken a first pass at reducing noise.  The goal is to avoid allowing sharpening to accentuate the underlying image noise. Regardless of the order in the development module, lets first look at why noise forms in digital images and what can be done to reduce it before the image gets to Lightroom.

What is Digital Noise 

Noise generally appears as tiny dots of contrasting tone or color across an image area that should show smooth tones.  The pixels in a sensor are not perfect and they all emit a degree of noise along with the light signal they detect.  Several factors can make this more apparent in the final image.

Colonial Marquee, Noise removed and sharpened

Bright vs Dark Areas

Luminance & Color Noise in Shadows

Noise tends to be more obvious in darker areas of an image especially when the dark areas are lightened in post-processing.  It is part of the nature of digital sensors that the dark areas of an image are recorded with a smaller tonal range and thus a lower signal to noise ratio (S/N).  In these areas, the noise can overwhelm the recorded brightness.  The noise in the bright areas is the same, but it is overwhelmed by the strength of the actual signal. This is one reason why it is recommended that images be “exposed to the right”.  “Blowing out” of the highlight should be avoided, but, the brighter that the shadows are recorded, the better will be the signal to noise and less noise will be apparent in the vulnerable dark regions.  In the final image, the shadows can be easily darkened in post processing.

ISO

ISO 1600 Noise, Obama in Keene NH, 2007

Noise becomes more apparent as ISO is increased.  Elevated ISOs work by increasing the signal intensity, but the noise is also increased.  Many new cameras have built-in noise reduction for high ISOs, but it is always best to shoot at the lowest ISO compatible with the shooting situation.

Pixel Size and Density

Stonewall Barn,  Canon G11, 10MP Small Sensor

As a rule, larger sensors produce images with less noise.  If you plan to blow-up your image to 20”x30”, don’t shoot it with your smart phone.  This related to the size of the individual pixels and how closely they are packed on the sensor.  A 14MP sensor crammed into a smart phone must have pixels which are much smaller than those in a 14 MP sensor on a full frame DSLR.  The small pixels each “see” less light and therefore must amplify the signal – and inevitably the noise.  The image from a 21MP sensor may have higher resolution than a 12MP sensor of the same size, but the 12 MP pixels can be bigger and therefore result in less noise.

Exposure Length

One Second Exposure, Lower Purgatory Falls

Longer exposures can introduce more noise into the image.  During long exposures, the pixels heat-up which results in more noise being produced. Also, during longer exposures, there is more opportunity for random static to add noise.  The impact of long exposures varies from camera to camera and some experimenting might be necessary to discover your camera’s tolerance for prolonged shutter speeds.

Balancing Factors

Lower Purgatory Falls, Wilton, NH

 

All photography is compromise.  If you lower your ISO to reduce noise, you may need to increase the shutter speed which will have the opposite effect.  When not constrained by the need to freeze action, I generally lean toward longer exposures, since it may take a shutter speed of a minute or more before heat will build-up to the point of causing significant noise.

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Noise Reduction in Lightroom CC

Detail Panel

Ok, you have pulled out your full sized sensor camera, lowered your ISO and exposed to the right, now what can Lightroom do to reduce any residual noise?

The Noise Reduction Panel performs separate adjustments on two types of noise, Luminance and color.  Let’s start with the easier of the two.

Color Noise

Color & Luminance Noise

Color noise appears as spots of aberrant color seen best when zoomed in to darker areas of the image. This noise often goes unseen since Lightroom, by default, presets color noise reduction to 25.  This is often sufficient to control the color artifacts and further adjustments may be unnecessary.  If you reduce the setting to zero you can see the underlying noise and higher levels of correction may rarely be required in especially noisy images.  The other two sliders seldom require adjustment.  The Detail Slider sets the threshold for what Lightroom will consider as noise.  Generally the default of 50 works well.  The Smoothness slider helps to smooth out larger blotches of color noise.

 

Luminance Noise

Color Noise Reduced, Luminance Noise Remains

Luminance noise is more difficult, both because it is generally more prominent, and because its limitation must be balanced against a loss of image detail.  Here, as in so much of photography, only you can decide where the best balance lies.  The major adjustment occurs with the Luminance Slider.  As it is increased, the coarse appearance of the noise fads, but along with this effect comes a steady loss of image detail, to the point that the image can have an overly smooth plastic look.  It is helpful to judge this effect both zoomed in and on the full image.  Some areas of

Luminance & Color Noise Reduced

smooth tone, such as the sky or skin may benefit from great greater noise reduction, but remember Lightroom's noise reduction is a global tool.  Both noise reduction and sharpening can be applied to select areas of the image with the local adjustment tools, but the effects don’t have the fine controls available in the Detail Panel.  In Photoshop, selective masking allows better control of local detail adjustments.

Local Brush to apply Noise Reduction Selectively to the Background (Red Mask)

The other two sliders in the Luminance Panel control the amount of preservation of image detail and contrast and can be adjusted to taste.

Final Obama Image, Keene State College Rally 2007

This is just a brief review of the sophisticated noise controls in Lightroom CC.  A more detailed discussion could not replace what can be learned by simply playing with the sliders.  Try them from their lowest to maximum levels, studying their effects at various magnifications.  Have fun and remember, this is Lightroom, everything is reversible, you can’t explode your precious image.

Jeff Newcomer

partridgebrookreflections.com

603-363-8338

Sharpening in Lightroom CC

Chesterfield New Hampshire Storm / Little Sharpening Needed

Thompson Brook Alstead NH

I have a great group of students gathered around my dining room table for this winter’s Adobe Lightroom Class.  They are smart, energetic and ask really good questions – LOTS of questions.  As a result, after two classes on the Library Module, I still have more to cover.  I’ll finish up next week, and then I hope to get a good start on the really fun stuff, Development.  It looks like my plan for a five-week course may expand to six.  I don’t care.  Its winter, and what else do I have to do?  Besides I love talking about this stuff.  

Since I’m pressed for time and I’m working on it anyway, This seems like a good opportunity to review a component of the development module which seems to one of the most confusing, sharpening.

Thompson Brook Reeds at 1:1

Why do digital Images Need Sharpening?

Soft Edge

When examined closely, digital images always have some softness, which is most noticeable along sharp edges.  This is seen as I zoom in to 4:1 on a collection of reeds, contrasting with the snow across from Thompson Brook in Alstead New Hampshire.  The individual pixels of a sensor each record an average of the amount of light striking them.  If a razor-sharp edge between bright and dark, such as created by these branches, crosses the middle of a single pixel it will record the average of that dark and bright, that means it will show a middle gray. 

Heavily "Sharpened" : Amount 150

 

 Sensors can never record a perfectly sharp edge but will have a scatter of gray tones along the edge, and that softens the sharpness.  Higher resolution sensors will have less of this effect, but it will always occur on images recorded with pixels.  Sharpening creates a greater contrast between dark and light but doesn’t eliminate the effect.

“Sharpening”

Softness always happens, but editing programs such as Photoshop and Lightroom have sophisticated tools to help reduce the appearance of softness.  It is worth stressing that Sharpening Tools make images LOOK sharper even though they can’t actually sharpen the edges.

Sharpening in programs such as Lightroom work by increasing the contrast between the light and dark sides of an edge.  It does this by lightening along the bright side of the edge and darkening along the dark side. When done subtlety, the results can appear as a sharpening of the edge, but when taken to excess halos can become apparent and excessive noise can be created.  The sharpening controls are designed to find the best balance of this effect for each image, but, as you will see below,  it is often helpful to understand theses controls by experimenting with their extremes. 



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Before You Sharpen

Before you dive into the Sharpening Panel a few points are worth mentioning.

Sharp Focus

First, no amount of sharpening can fully correct an image which is out of focus.  Start with a shapely focused image and if only parts of the image are in focus, make sure that you zoom in on that part of the picture before sharpening.

1:1

Generally you should do the sharpening at 1:1 magnification, but I will be zooming in closer to better show what is happening during the process.

1:1 View

Input Sharpening

The sharpening in the Lightroom Develop Module is called “Input Sharpening”.   It is your first pass at sharpening but shouldn’t be the last.  In Lightroom you are sharpening the image for the screen, but you should not over do it.  Images generally should receive a final “Output” sharpening after they have been edited and resized for a particular purpose.  An option

Export "Output" Sharpening

is available in Lightroom's Export Panel to sharpen the exported images for the intended purpose. Choices include, sharpening for the screen (web), and for printing to either Mat or Glossy paper.  These generic adjustments often work well, but I generally prefer to make my final output sharpening from within Photoshop.  

The important thing to remember is that Lightroom's input sharpening is not your final opportunity to sharpen the image, and therefore it is best to make the adjustment on the conservative side.  That being said, I like the way Lightroom performs sharpening, and I find that I have to do a lot less in Photoshop if my images have been pre-processed in Lightroom.

Gilsum, New Hampshire

Noise Reduction

Particularly on especially noisy images, I find it helpful to do some preliminary noise reduction before I sharpen.  Noise reduction is performed in the panel just below the Sharpening tools and is worthy of a separate discussion, which I will save for next week, but when done first it can avoid the sharpening of noise artifact.

The “Science” of Sharpening

Finally sharpening is not an exact science.  Everyone must judge for themselves the optimal balance of apparent sharpness and artifact.  Despite what you may read in many on-line articles, there is no magic formula for the best sharpness in all situations.  The Sharpening Tool Panel can help you better see the effects but the final decision is yours.


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The Sliders 

Sharpening Area

Ok, you have zoomed into a focused area of your image showing some edges that should be sharp.  Now what?  There are the four basic adjustment sliders which all work together to get the best results, Amount, Radius, Detail and Masking.  Since RAW images always benefit from sharpening, Lightroom sets initial default values to get you started.

Default Settings / Zoomed to 4:1

Amount

Extreme Settings / Banding along the edge

Simply stated, the Amount Slider controls the amount of sharpening.  What that really means is that it controls the extent to which an edge is accentuated by bands of darkening on the dark side and lightening on the light side. The higher the number, the greater the effect.  If you move too far you will be able to appreciate halos of light and dark on either side of the edge and you will also see increasing noise.  Raw images open with the Amount set at a default of 25.  I typically vary the value from 50-100 with images containing a lot of fine detail often tolerating higher levels.  The extreme settings, shown here for illustration, include both the maximal sharpening and the radius at its greatest extent. 

Alt/Opt

"Alt" / "Opt" for Amount

Sharpening is strictly a luminance effect and not related to color   Therefore the effect can be better seen by holding down to “Alt” key (“Opt” on a MAC) to remove the distracting color.  The same key can be used on the Radius and Detail sliders to show their effects more clearly.  I have never found that this modifier makes a significant difference in my ability to follow the effects of these adjustments, but you should try it for yourself.   As we will see the Alt/Opt key has a somewhat different effect on the Masking slider.

Radius 

Radius controls the width of the bands of “sharpening effect”.  The default value of 1 means that the effect covers one pixel around the edge.  Higher values will widen the sharpening effect but also increase the appearance of halos.  I tend to leave this at its default of one and seldom go above 1.5.  The best Radius setting will depend on the size of the image.  A value of 1-2 works well on large images, such as the 4480 x 6720 pixels from my 5D Mark IV,  but this is obviously excessive for sharpening done on my web images, which have a long dimension of 950 pixels.  For the web, I generally start at a radius of 0.5.

Detail

High Detail / Heavy Noise

The Detail Slider controls the extent to which the finer detail in the image is sharpened.  At 0 only the most prominent edges will receive sharpening and, as the value increases toward the maximum of 100, more of the fine detail of the image will be affected and also image noise will be accentuated.

Masking

Masking with "Alt" / "Opt"

The Masking slider controls how much of the image receives the sharpening effect.  You want to limit sharpening to areas of important detail and mask it from regions of naturally soft continuous tone such as sky or water.  In portraits, the areas around the eyes and mouth may benefit from sharpening but not the skin of the cheeks and forehead.  Holding down the “Alt” key (“Opt” for Macs - must I keep saying that?!) while moving the Masking slider to the right, areas of black will increasingly appear.  The black areas are masked from the sharpening.  The slider can be moved until the sharpening is restricted to those areas of detail where the effect will be beneficial.  Masking of sharpening can be done more accurately with localized brushes in Lightroom or Photoshop, but the Masking slider does a surprisingly good job.  

Loose Masked Sharpening

When zoomed in closely you may notice that your masking does not tightly align with the edges and, if there is excessive noise, this may show as a noisy border along sharpened edges.  This is seen most clearly when closely zoomed and can be reduced by expanding the masking or reducing noise by using the Detail or sharpening sliders.

Fringing of Noise following Masking

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My Approach

As I said, there is no correct formula for sharpening and the best approach is to go back and forth with the sliders to find a good balance.  Remember that this is Lightroom therefore and any changes you make can be reversed.  Nothing you do will explode your image.  That's being said, here is my rough approach.

Snowing Hill, Walpole, NH

I start with the Amount Slider and vary it to find a spot that begins to result in unacceptable artifacts.  Then I pull back a bit.  I generally keep the radius at one.  I then reduce the Detail slider  from its default setting to zero, which has the effect of softening the image.  I then move the Detail slider up until I start seeing fine or “high frequency” noise appear and pull back slightly when the noise reaches that nebulous “unacceptable” point. 

  At this point, I will use the masking tool to make final adjustments in the amount of the image which is affected by the sharpening. 

Final Settings / A Compromise

My final step is to turn the Sharpening Effect on and off using the switch at the top left of the Detail Panel.  This reassures me that I have actually created the appearance of increased sharpening.

Sharpening in Lightroom should not be intimidating.  Just remember to use a light touch, knowing that it will not be the last time that you will apply this effect.  Then trust your eye.  Have fun.

Jeff Newcomer
partridgebrookreflections.com
603-363-8338