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.
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.
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
Before I go any further, it's important to know exactly which of Canon's DSLRs this information applies to:
- EOS-1D X Mark II
- EOS-1D X
- EOS 5D Mark IV
- EOS 5Ds R
- EOS 5Ds
- EOS 5D Mark III
- EOS 6D
- EOS 6D Mark II
- EOS 7D Mark II
- EOS 80D
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:
- Tripod use is required, especially as there is no option to align the images in-camera.
- Any subject that moves during the 9-image capture duration will be blurred.
- You must first shoot a base image before selecting the Multiple Exposure options, as designating a base image is required. Therefore, there will be delay between the first image and the following 8 images.
- In-camera lens profile corrections are not supported.
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.
- If photographing a lighted sign that lights up sequentially (as if being handwritten), and there is only a small portion of time when the sign is completely illuminated. If you were to use a longer shutter speed, the illumination of the sign may not be even. However, if you time your 9 shots when the sign is completely illuminated, you can avoid the uneven brightness.
- If photographing a moderately busy street scene, but you do not want pedestrians or traffic in the image. You can easily time your images so as not to include pedestrians or traffic in the final image.
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
- As previously mentioned, the best noise reduction will result from the combining highest possible number of shots (max 9)
- With Multiple Exposures set to Function and Control Priority (On:Func/Ctrl), the source files will be saved along with the final combined result. However, if using continuous shooting, the burst rate will be significantly reduced.
- With Multiple Exposures set to Continuous Shooting Priority (On:ContShtng), the source files will not be saved (only the final result) but continuous shooting will operate at a normal-for-the-circumstances rate.
- You can get similar results in post processing by combining separate exposures in Photoshop CC by using File/Scripts/Statistics and stacking your images using "Mean."
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.