Rudy Winston
Rudy Winston

Rudy Winston has over 14 years experience with Canon USA's Pro Products team, and has been responsible during that time for training Canon's staff on new products, creating presentations for customers and dealers, numerous writing projects, and providing technical assistance to professional and amateur photographers.

High ISO Noise Reduction

March 28, 2011

For those cameras where High ISO Noise Reduction is simply an off-on option, you're entitled to wonder why one wouldn't simply turn it on and leave it on all the time.

High ISO Noise Reduction is a new feature that’s appeared on recent EOS Digital SLRs.  As of early 2009, it's a Custom Function choice in the EOS Rebel XS and XSi, EOS 40D and 50D, EOS 5D Mark II, and both the EOS-1D Mark III and EOS-1Ds Mark III models.  It’s totally different from the Long Exposure Noise Reduction which has been a part of EOS digital cameras for some time, and we’ll outline here some of the characteristics of this new option.  If you have an earlier EOS model, such as the EOS 30D, Rebel XT or XTi, or EOS 5D, High ISO Noise Reduction is not available in-camera.  But even here, if you shoot RAW images and process them in Canon’s Digital Photo Professional software (version 3.2 or higher), it’s possible to accomplish very similar results using the software’s noise reduction tools.

High ISO Noise:

Any time a digital camera is used at higher ISO settings, it will tend to generate more noise in the pictures it produces.  With modern digital SLRs, most users would agree that noise becomes an issue at ISOs such as 1600 or 3200.  With compact, fixed-lens digital cameras, for technical reasons, noise can sometimes become a visible problem at ISOs as low as 200.

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 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.  Likewise, you’re much more likely to see noise in high ISO files from any digital camera if images are underexposed in any way.  Some users will intentionally try to over-expose their high ISO images slightly, by perhaps 1/3 to ½ of a stop, to reduce the visible level of 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 in an image if you lighten it in the computer, but it’s not a free lunch.  Even if you originally shot at an ISO such as 100 or 200 with an EOS digital SLR (settings normally considered to have very little visible noise), by lightening the mid-tones and shadows, you greatly increase the level of digital noise in these areas.

Types of high ISO noise:

When you look close, you’ll see that high ISO digital images have two types of noise.

Luminance Noise is the gray- or black-colored noise or “grain” that you often see when you look at a magnified view of an image on-screen, or 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 is also a 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 far less impact on fine details of your subjects, so it can often be reduced or removed without appearing to blur or soften your images.


Canon’s High ISO Noise Reduction:

Canon EOS digital SLRs with High ISO Noise Reduction tackle the issue in a couple of different ways.  Cameras like the EOS-1D Mark III and EOS-1Ds Mark III, EOS 40D, and EOS Rebel XS/XSi offer two options -- either ON or OFF.  By default, when you take the camera out of the box, these cameras have High ISO NR turned off.

With these models, High ISO Noise Reduction essentially attacks visible chrominance noise, reducing the pastel-colored effect you sometimes can see when you look closely at skin tones and other plain, solid areas.  It's important to understand that in order to preserve actual subject sharpness and detail, Luminance Noise is essentially left untouched by turning the High ISO Noise Reduction to "on" with these cameras.

However, Canon's newest models with the high-performance DIGIC 4 processor use a more advanced form of in-camera High ISO Noise Reduction.  The EOS 50D and EOS 5D Mark II leverage the power of the new processor to provide excellent, low-noise preformance at substantial high ISOs.  It's part of the reason, for example, that excellent images can be taken with the EOS 5D Mark II at ISOs up to 6400, and in a pinch, ISOs up to 25,600 are useable.

 

The EOS 50D and EOS 5D Mark II have four settings for High ISO Noise Reduction, within the camera's Custom Functions:  OFF,  Low,  Standard, and Strong.  Here's a key difference, however, between those two, and other models like the EOS 40D or the Rebel XS and XSi: With the newest DIGIC 4 cameras, the default 'out of the box' setting for High ISO Noise Reduction is STANDARD, not OFF.  Upon close examination, users will find that the Low setting applies correction strictly to the Chrominance Noise;  the Standard setting aggressively attacks chrominance noise and has a very slight effect on Luminance noise, and the Strong setting applies considerably more reduction to Luminance noise (especially with the EOS 50D).  This may have an impact on how fine details appear.  

Users should experiment with different settings, preferably with subject, exposure and ISO settings remaining constant, to see for themselves what differences they'll notice at ISOs such as 1600 and above.  JPEG images are ideal to observe the effect of High ISO Noise Reduction with the camera's image processing.  You may find, for instance, that the Low or Standard settings are fine unless you use a separate Custom Function to expand your ISO above the camera's normal highest setting.

High ISO Noise Reduction On or Off: Why not just leave it on all the time?

For those cameras where High ISO Noise Reduction is simply an off-on option, you're entitled to wonder why one wouldn't simply turn it on and leave it on all the time.  Why, instead, is it an optional feature?  There are two primary reasons:

•    In some cases, critical users may see a slight shift in color in images taken with High ISO Noise Reduction turned on.

•    For technical reasons, there’s a significant drop in the camera’s “burst rate” when High ISO Noise Reduction is active.  You can still set your camera to its fastest continuous shooting setting, such as 6.5 fps on the EOS 40D, but you’ll only be able to shoot a handful of shots in a continuous burst before the camera slows down if the High ISO Noise Reduction is active.

Effect of High ISO Noise Reduction on Burst Rates*

 

Burst Rate (High ISO NR off)

Burst Rate (High ISO NR on)

EOS-1Ds Mark III

42

4

EOS-1D Mark III

110

14

EOS 40D

75

6

EOS Rebel XSi

53

2

* Please note – figures are for camera set to shoot Large/Fine, full-resolution JPEG images, at ISO 100.  Figures are approximate, and will vary if ISOs are raised or certain other camera features are activated. 

One of the advances with the DIGIC 4 processor is that its greater power means far less impact on burst rates with High ISO Noise Reduction in effect.  In fact, at the Low or Standard settings, burst rates are the same as if the feature is turned off.  It's only when you set this Custom Function to "Strong" that you encounter a drop in the available burst rate (this is a key reason why High ISO Noise Reduction is set to Standard as the factory-default setting).  As of January 2009, this information only applies to the EOS 50D and EOS 5D Mark II cameras.


Can the High ISO Noise Reduction be used for low-ISO pictures?

Good question.  The answer is yes — once you’ve activated this Custom Function, you can use it for shots taken at any ISO setting, even if you’re shooting outdoors in bright sunlight at ISO 100.  If you sometimes use image-editing software to lighten dark shadow areas in your pictures, there’s a good chance that High ISO Noise Reduction will reduce the resulting level of digital noise in your mid-tones and shadows.

So even though the name suggests that it’s only for high-ISO shots, in fact, you can use it any time you like.  Just remember, you must activate it first in the Custom Functions menu of those EOS models that have this feature.

How does High ISO Noise Reduction work with JPEG images?

Quite effectively, especially at ISOs where chrominance noise tends to become visible (such as ISO 1600 and above).  JPEG images are entirely processed into finished files in your camera, and then written to the memory card.  All color and detail information is calculated and written into your final image.  So settings affecting image quality that you make in the camera are immediately visible in finished JPEG images.

You may want to experiment by shooting a scene or subject in low light, at a high ISO setting, and taking two shots — one with High ISO Noise Reduction turned off, and another of the same scene with the Custom Function turned on.  Compare the two images by viewing them on-screen at 50% or 100% magnification, or by making a letter-size or larger print of each file.  At high ISOs, you should be able to see the differences by looking at mid-tone or shadow areas closely.  Each photographer should make up his or her mind, based on their shooting conditions and needs, but High ISO Noise Reduction can be very useful for JPEG shooters who find themselves needing to work at ISOs such as 800 and above.

How about with RAW images?

Here, the results are much more dependent upon how you process your RAW files.  Remember:  unlike a JPEG image, with RAW files, the finished image is “assembled” in your computer, with whatever RAW file processing software you elect to use.  Here’s a quick break-down:

•   Canon’s RAW Image Task software:
(Included with some EOS Digital SLRs, it’s a part of the ZoomBrowser EX software for Windows, or the ImageBrowser software for Macintosh OS X computers. )  One characteristic of RAW Image Task is that it tries to give very similar results to the in-camera processing you’d see in a JPEG image file.  In other words, it attempts to process RAW images so they look very similar to how the camera’s DIGIC processor would generate finished JPEG files.
Because of this, Highlight Tone Priority is also very useful when RAW images are processed using either ZoomBrowser EX or ImageBrowser software.  You’ll often see a visible reduction in chrominance noise, if High ISO Auto was active in-camera when you took the shot.

Please note that the RAW Image Task software is not included with EOS 50D and 5D Mark II cameras, and it's not compatible with their RAW files.

•     Canon Digital Photo Professional software (“DPP”) :
(Stand-alone program also included with EOS Digital SLRs)  Unlike RAW Image Task, DPP software uses different calculations for processing the finished “look” of Canon EOS RAW files.  It does not attempt to faithfully duplicate the in-camera DIGIC processor, but rather produces high-quality RAW images with a look of its own.  Some critical users feel that Digital Photo Professional software gives the finest overall image quality for RAW images of any available software.

 However, while DPP can read the camera settings in effect at the time the images are taken, it tends to downplay the effect of the camera’s High ISO Noise Reduction.  You may see little difference if you compare two RAW files, one with NR active, and one with it turned off. However, DPP has another option:  its own separate Noise Reduction tools.  For RAW images, DPP allows the option to reduce chrominance or luminance noise, or both.  And, unlike the camera’s High ISO Noise Reduction, you can apply it in medium or strong quantities, using a variable on-screen slider.  Finally, if you don’t shoot RAW images, Digital Photo Professional still has an answer.  For JPEG images, or TIFFs that you’ve created in an image-editing program, you can reduce chrominance noise using a slider control on-screen.

•    Third-party RAW file software programs:
Virtually all third-party RAW file software programs, such as Adobe’s Camera Raw™ software, will ignore in-camera settings such as High ISO Noise Reduction.  Therefore, if you use another company’s software, you’ll generally have to use the software’s own tools to change the look of your finished pictures.  Don’t expect the High ISO Noise Reduction you may have set in-camera to have any effect with most third-party software programs. You can easily experiment to see what impact in-camera settings may have with your third-party software of choice — take a RAW image with High ISO Noise Reduction or a similar EOS feature off, and then a second RAW image with the feature turned on.  Process both in the third-party software, and compare the finished results in Photoshop or another image-editing program, and view them at about 50% to 100% magnification on-screen.

Summary:

The new High ISO Noise Reduction feature gives a further option for users of recent EOS cameras to improve the quality of their images.  It has a noticeable impact on the level of visible noise in shots taken at higher ISO levels, and can even have a positive effect on an image at lower ISOs (if it's subsequently lightened using image-editing software).  Especially if you shoot JPEG images, we strongly recommend trying the different settings to see the effect it will have on your images.  For RAW shooters, it can also make a noticeable difference in how Canon's software processes your images -- although with Digital Photo Professional software, you're free to independently adjust chrominance and luminance noise reduction beyond the initial in-camera settings.  More than ever, today's digital SLRs are capable of excellent pictures at ISOs that were unthinkable just a few years ago.  With Canon's most recent digital SLRs, the High ISO Noise Reduction technology is an important reason why.

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