by Sean Setters
Aside from the Rebel T6, all of Canon DSLRs currently produced feature Multi-Shot Noise Reduction (MSNR). With the feature enabled, your camera takes a burst of 4 images which are combined and output to a JPEG file with less visible noise compared to a single exposure.
Unfortunately, there are many downsides to using MSNR. For a good overview of those downsides, let's take a look at a couple of paragraphs from Bryan's review of the 5D Mark IV:
Multi Shot Noise Reduction (MSNR) is one of the additional in-camera options available in many of the latest EOS models including the 5D IV. MSNR merges information from multiple (four) exposures taken in a full-frame-rate burst into a reduced noise image. The concept makes a lot of sense. MSNR generally provides a remarkable one stop or more of noise reduction, but ... I still have not found a compelling use for this feature.Fortunately, with several of Canon's upper-level DSLRS, there's a slightly better way to accomplish the same goal. It involves many of the same compromises as Multi Shot Noise Reduction, but instead of being limited to JPEG output, you can output a RAW file instead.The downsides to Multi Shot Noise Reduction include: MSNR is currently available only with JPG output (I would like to see this feature added to Canon's Digital Photo Pro software for RAW capture processing – perhaps as another HDR preset). Multi-Shot Noise Reduction is not so useful with moving subjects (or with a moving camera). Long exposure NR, Dust Delete Data, Multiple Exposure and HDR Mode must be set to off to enable MSNR. The 5D IV reverts back to Standard NR in Auto/Basic zone modes, during video recording, in Bulb mode and when the camera is powered off. Flash is not supported in MSNR mode. After the 4 shot burst is captured, the camera remains "busy" for a noticeable period of time while processing the merged image. So, while this feature is a nice idea, its limitations make it less useful in real-world applications. I am far more likely to use a low ISO setting with a longer exposure when shooting stationary subjects from a tripod.
Before I go any further, it's important to know exactly which of Canon's DSLRs this information applies to:
The secret is to use your camera's Multiple Exposures feature and set the Multiple Exposure Control Method to "Average." By setting the desired number of shots to 9 (the max), noise in the combined image will be greatly reduced.
The best part about using this technique is that it enables reduced noise to be captured in a RAW file rather than JPEG. However, drawbacks of using this method include:
With the drawbacks listed above in mind, you may be wondering what situations would benefit from using the Noise Reduction through Multiple Exposure technique. Here are a few ideas I came up with.
To get a better understanding of just how significant the noise in your RAW images can be reduced using this technique, download the full resolution 7D Mark II ISO 12800 single exposure and 7D Mark II ISO 12800 multiple exposure files and compare the noise for yourself. The RAW files were processed identically (except for white balance) in Adobe Camera RAW with no noise reduction applied before the JPEG conversion. Note that the sample images were not taken under circumstances where this technique would be especially beneficial, as a longer shutter speed could easily have been used (they are only used for noise reduction demonstration purposes).
Tips for Using Multiple Exposures (Average) for Noise Reduction
While the technique may not be feasible under a wide variety of situations, the noise reduction benefits will certainly be worthwhile in the specific situations where this technique can be employed.
Can you think of more situations where this technique might be useful and advantageous? Let us know in the comments.