High ISO Noise Reduction

December 23, 2015

This article was originally published on March 28, 2011 and has been updated to include current product information.

High ISO Noise Reduction has been a feature in digital cameras for years. Since roughly 2008, newly-introduced Canon EOS DSLRs have gone beyond simple “On-Off” settings for High ISO Noise Reduction, with various options for reducing digital noise at elevated ISO settings. We’ll explore the nature of noise in our digital image files, as well as the technologies to reduce it, in this article.

Understand that what Canon calls “High ISO Noise Reduction” is totally different and separate from another menu setting, “Long Exposure Noise Reduction.” The latter is technology to combat the so-called fixed pattern noise that can develop as shutter speeds become progressively longer — a common issue in long night exposures and so on.
The two settings in an EOS camera’s menu are independent of each other. Long Exposure Noise Reduction — even if you’ve turned it on in the menu — only affects images taken at shutter speeds one second or longer; if you shoot at faster shutter speeds, it’s inactive. The two types of noise reduction can be combined in-camera, if you desire (there’s one exception, which we’ll detail later.) Long Exposure Noise Reduction is useful for those who shoot night or similar low-light images at slow shutter speeds, but our focus in this article is High ISO Noise Reduction.

 

 

What is High ISO Noise?

High ISO noise is the speckled, grainy look you can see at high magnifications in a digital image file. The higher your camera’s ISO is set, the more likely you are to encounter this. Digital noise tends to be most visible in mid-tone to darker areas of a scene, especially if they’re rather plain and don’t have a lot of detail or texture.
When you look closely, you’ll see that high ISO digital images actually can show two distinct primary types of digital noise:

  • Luminance Noise: This is the gray or black-colored noise or “grain” you often see in a magnified view of an image, either on-screen or when you closely examine a large print. Actual subject detail is a component of the luminance noise, so you want to be very careful about simply removing this noise altogether — it’s very easy to blur-out the noise and end up with a smooth picture that’s totally lacking in subject detail.
  • Chrominance Noise: This type of digital noise is also part of high-ISO images, but it’s different. It’s the pastel-colored, speckled noise you sometimes see in mid-tone or shadow areas, upon close inspection. This noise has less impact on fine details of your subjects, so it often can be reduced or removed without appearing to blur or soften your images. However, a heavy-handed approach to minimizing this type of noise can result in unexpected color shifts in your images.

 

 

Any time a digital camera is used at higher ISO settings, it will tend to generate more noise in the pictures it produces. While opinions vary about what constitutes objectionable levels of digital noise, most DSLR shooters would probably agree that good, useable images can be made with today’s cameras at ISOs up to or even beyond ISO 3,200. With compact, fixed-lens cameras, such as Canon’s PowerShot models, there are technical issues — primarily much smaller imaging sensors — that make digital noise more visible at lower ISO settings. Quality-conscious users of compact cameras might feel settings above ISO 800 are prone to visible high ISO noise.

Digital noise tends to be most noticeable in plain, solid areas of a subject, especially if they’re mid-tone or dark areas. A photographer shooting ice hockey pictures, for instance, may see much less overall noise in his or her files than a photographer taking available-light pictures in a darkened theater, even if both are working at the same ISO. The light-colored surroundings in a typical hockey rink make noise harder to detect.

Likewise, it’s much more probable you’ll see noise in your images if they’re underexposed in any way. Some users will intentionally try to over-expose their high ISO images slightly, perhaps by 1/3 to 1/2 of a stop, to reduce the levels of visible noise.

Even if you shoot at lower ISOs, you can still encounter digital noise in your images if you deliberately lighten them in an image-editing software program. A surprising amount of detail can be gathered from dark shadow areas of an image if you lighten it in the computer, but it’s not a free lunch. Even if you originally shot at a low ISO with an EOS DSLR, such as ISO 100 or 200 (settings normally considered to have very little visible noise), if you lighten mid-tones and shadows in the computer, you run the risk of greatly increasing the level of noise in these areas.

What is High ISO Noise Reduction?

It sounds very elementary, but there’s additional information that digital camera users should understand about noise reduction and how it works in-camera. To begin, we should look at what digital noise really is.

Digital noise can have numerous sources, but the impact ends up being very similar. In areas of a subject or scene where we expect continuous, steady repetition of tones and pixel brightness, we can instead see variations from one pixel to the next. Typically, in high ISO scenarios, we see scattered, irregular patterns of darker pixels, and sometimes the aforementioned stray colored pixels, producing color artifacts where a subject should exhibit none.

Noise reduction technology basically examines the different brightness values from one pixel to the next, factoring in brightness levels of pixels within a given area. Where it observes pixels with differing (and especially lower) brightness than their immediate neighboring pixels, this may be digital noise.

But there’s an important catch — pixel to pixel brightness variations can also be actual subject detail. Think about a highly magnified view of a person’s eye in a portrait, for instance. Changes from mid-tone pixel brightness to dark pixels might be the subject’s eyelashes or possibly texture in their skin from the lighting being used.

Accordingly, any noise reduction technology has to apply a series of very sophisticated calculations and algorithms across the entire image to assess these brightness variations at the pixel level and to “decide” whether they indicate digital noise (OK to smooth out) or actual subject texture or detail (which we want to preserve). Especially with luminance noise (again, that’s the monochromic type of “salt and pepper” type noise often seen in high ISO images), powerful processing is needed to give us low noise but preserve good, sharp detail.

Even with this advanced technology occurring under the hood, it’s a fact that strong levels of noise reduction will usually reduce actual subject detail and texture. This is an important consideration if you’re using a recent camera with variable levels of in-camera noise reduction.

 

Quick history of Canon’s High ISO Noise Reduction
  • Early EOS models: While digital noise at higher ISOs has always been with us in the digital camera age, user-adjustable technology to counter it hasn’t always been. In fact, older Canon EOS DSLRs (early Rebel models such as the XT or XTi, original EOS 5D, and mid-range cameras like the EOS 20D or EOS 30D) had no high ISO noise reduction settings in-camera. A certain amount of built-in correction was performed in-camera as JPEG files were processed, before they were written to the memory card. With RAW files from these early cameras, users did have tools in RAW processing software (such as early versions of Canon’s Digital Photo Professional [DPP] software) to define the level of noise reduction in a finished, processed file.
  • The next step — High ISO Noise Reduction with on-off control: As time went on, Canon engineers did add menu settings for High ISO Noise Reduction with a simple choice of “Off” or “On.” Users who wanted to minimize any loss of detail or sharpness (more on this later) could opt to disable any in-camera noise reduction; users who wanted minimal time at the computer could tell the camera to apply a reduction of noise in JPEG files and “tag” RAW files with a standard level of reduction once they were brought into software like Canon’s DPP.
    Cameras like the EOS 40D, Rebel XS and XSi, and EOS-1D Mark III introduced on-off control High ISO Noise Reduction in this form. Normally, you’ll find that these cameras tend to attack mostly chrominance noise in high ISO files, when their noise reduction has been turned on in the menu. And, by default, the camera’s High ISO Noise Reduction is turned off.
  • The present — variable in-camera noise reduction: More advanced handling of High ISO Noise Reduction began around 2008, with cameras like the Canon EOS 50D, EOS 5D Mark II, and Rebel T1i (EOS 500D) models. These added the ability to define the level of noise reduction, not simply have it on or off. This has been carried over into subsequent models and is essentially the same system in use on EOS DSLRs today.
Low, Standard, and Strong — today’s High ISO Noise Reduction

As of late 2015, all current EOS DSLRs offer adjustable settings for the degree of in-camera, high ISO noise reduction that’s applied to images. Particularly for users who shoot JPEG original image files or record HD video* with EOS DSLRs, understanding what to expect from the High ISO Noise Reduction settings can be important.

  • Off: No noise reduction is applied. If you know you’ll only be at low ISO settings, this buys you a small degree of potential extra detail in your files. As ISOs rise, there will definitely be progressively more visible chrominance and luminance noise. If you shoot RAW files and prefer to process them using another company’s RAW processing software, you may find this to be a practical starting point. Most third-party RAW process software ignores in-camera menu commands for noise reduction, relying instead on the software’s own tools to perform this task. Below is an original full image, taken at ISO 12,800, and a small cropped section, showing the impact of varying levels of High ISO Noise Reduction. These are a good indication, at least with APS-C size sensor cameras, of what you might expect if the camera is set to high ISO levels.
  • Low: This tends to apply reduction to chromatic noise in digital files, with minimal impact on luminance noise. Because luminance noise is touched lightly (if at all), this setting tends to preserve the most subject detail and texture — at the expense of more readily visible noise as ISO settings rise.
  • Standard: This is the factory default setting for recent Canon EOS cameras. Standard noise reduction aggressively counters chrominance noise and begins to smooth the impact of luminance noise in image files. As with all Canon High ISO Noise Reduction, the Standard setting is “smart” about its approach to attacking noise… at low ISO settings, there’s little intervention; as ISOs and noise get higher, the level of noise reduction increases. There’s a bit of a loss of subject detail and texture if you shoot at really high ISOs, but experiment to see if you feel this is a problem for you.
  • Strong: As the name suggests, it’s the strongest levels of noise reduction. But think carefully before applying this setting, especially if you work at high ISO levels. “Strong” High ISO Noise Reduction applies aggressive reduction to luminance noise, considerably reducing the level of visible noise. With generally smooth subjects having little detail, this may be great. But subject texture and fine detail will be reduced as well. Likewise, this setting very strongly counters the pastel-colored chrominance noise. You’ll especially notice the impact of the “Strong” settings at high ISOs with cameras using the smaller image sensors because they’re more prone to digital noise — and require more correction — in the first place.
    With some EOS camera models, your menu may display “High” instead of the word Strong. In either case, all that we’ve discussed here applies.
    One other note about the Strong noise reduction option: with some older EOS cameras (EOS 5D Mark II and EOS 50D or 60D, for instance) there’s a noticeable drop in the number of shots you can take in one continuous burst because of the added processing involved. Your fastest frames-per-second rates aren’t affected, but the number of consecutive shots you can take often are. This is usually displayed on the far right of your viewfinder information.
  • Multi-shot noise reduction: This is a new High ISO Noise Reduction option, available on certain Canon EOS models — on the same menu screen as the options above would be. As its name suggests, Multi-shot noise reduction takes four separate images in rapid succession and using internal processing, combines them into a single finished image.
    This actually is a very effective method of in-camera noise reduction for high ISO shooting. It reduces noise to levels similar to the Strong setting, but with markedly more subject detail. Even though it’s at its best when mounted on a tripod or similar stable platform, it can be used in hand-held shooting if you’re careful to hold the camera very steadily. A few other points: each of the source images the camera takes will be at faster shutter speeds than a normal, single image would be, and the four initial source images are not saved on the memory card. And, Multi-shot noise reduction can only be used with JPEG original files (it’s grayed-out if you’re set for RAW images). Finally, unlike the other High ISO Noise Reduction settings, it cannot be combined with Long Exposure Noise Reduction.
    Because it takes four separate images and combines them into one final image, this isn’t the right option for high ISO shots of moving subjects or in situations where it would be difficult to hold the camera steadily. But for more controlled, low-light situations, it’s worth a try.

Photographers should experiment with these different settings, at various ISOs, and look at magnified images either in print or on-screen to see what tends to work best for them.

*Note: Application of High ISO Noise Reduction to video files varies, depending on camera model. As a general rule of thumb, Canon EOS cameras with DIGIC 4 processors do not apply High ISO Noise Reduction to video files — if it’s been set on the menu, it’s ignored. (EOS 5D Mark II, original EOS 7D, Rebel T3–T4 series models, etc. are among those that cannot use High ISO Noise Reduction when recording video.)

Is High ISO Noise Reduction only for high ISO shooting?

Not at all. It’s actually effective at any ISO, even low ISOs like 100 or 200. The noise reduction is sophisticated enough to lower its impact when there’s little noise present — as is usually the case at low ISOs — and increase its reduction strength as ISOs get higher. The impact, of course, tends to be most evident in images that are taken at high ISO levels. But quality-conscious shooters should experiment and evaluate its impact, even at lower ISOs. This is especially the case if you tend to lighten shadows using image-editing software after shooting and/or if you use Canon’s Highlight Tone Priority option.

 

Noise Reduction and RAW images

As is almost always the case, menu settings applied when you shoot RAW files will be “tagged” to each image you take. Then, if you process the RAW files in Canon’s Digital Photo Professional software, in-camera settings will be used as the starting point to modify the processing — unless you change them within DPP, which you certainly are free to do. DPP software, in fact, gives very precise and much more extensive control of noise reduction in Canon RAW images, allowing separate adjustments for both luminance and chrominance noise, and in much finer steps than the camera menu settings.

A few original RAW files, shot at various ISOs, and the noise reduction sliders in DPP are actually a great way to learn about the impact of the two different types of noise and what (if any) by-products result if you apply extensive noise reduction.

 

With the majority of third-party RAW processing software applications from other companies, most image-related settings from the camera’s menu are ignored and the software’s own basic default settings are used to process your RAW images. And, of course, most software has a host of on-screen options where you can make your own adjustments… in this case, that would be to alter the level of noise reduction in high ISO images. But it’s up to you to experiment and find settings that work for you; those described in this article assume you’ll either be using Canon’s software for RAW images or having the camera apply them directly to JPEG or video files.

 

Summary

High ISO Noise Reduction is a significant option for many users to improve their image quality. It can open the door to the right kind of correction you get at higher ISO settings and make high ISO shooting an even more viable tool. Even some of the most experienced professional photographers sometimes have to use a JPEG workflow to quickly meet deadlines or get images to a client. Knowing what the different High ISO Noise Reduction settings will do at various ISO levels can arm those shooters with the info they need to get the best image quality for the job at hand.

And for RAW image shooters, if you use Canon’s DPP software, the High ISO Noise Reduction settings you apply on your camera’s menu can still represent a time-saving and efficient starting point. You can, of course, completely change how noise reduction is performed during RAW image processing (and DPP offers extremely fine control of this, as mentioned previously), but knowing the camera settings and their impact can save some workflow time at the computer.

Most of all, though, today’s DSLRs are capable of superior pictures at ISO settings that were unthinkable just a few years ago. High ISO Noise Reduction opens the door to leveraging this potential in your image files and we urge critical photographers to experiment with it, get to know the feature and how it can best work for them.

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