Following are the 100% crop image quality comparisons included in most recent Canon EOS DSLR Reviews. Read about the Camera ISO noise tests in the help section to learn more about the tests and how they are conducted. A key take-away from that page is that noise reduction is completely off unless otherwise specified. And remember, the T4i results represent what you should expect from the T5i.
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While this comparison is primarily designed to show noise (and color), you can see the obvious difference in the T5i/T4i's sharpness compared to the other APS-C bodies including the T3i. As I said before, I welcome the increased sharpness, but increasing sharpness often increases the visibility of noise. You will see this when comparing the T4i to 60D.
The set of T4i Sharpness=0 results were processed with a sharpness setting of 0. These results are very similar to the T3i's results, both in terms of sharpness and noise levels. Essentially, the T5i/T4i's image quality matches the T3i's when the same amount of sharpening is added to both. The T3i has great image quality, so matching this image quality is very good.
In-camera noise reduction is standardly available in EOS DSLRs, and noise reduction is of course also available during post processing. The bottom three rows of results in the comparison above (and below) show examples of T4i noise reduction. All three NR examples utilized the Standard Picture Style in-camera with the default sharpness setting (so that the RAW NR results would match the JPG NR results). The default sharpening applied to these results examples the destructiveness of sharpening (look for halos around the low ISO color block examples). The noise reduction process is also destructive - I usually apply only light NR in my noisier images.
Multi-Shot Noise Reduction is new for EOS - and I was quite excited to see how the merging of multiple (four) exposures taken in a full-frame-rate burst could be used to reduce image noise. The concept makes a lot of sense. The bottom two NR examples provide a direct comparison with the standard NR and the Multi-Shot NR. There is definitely improvement with MS NR - a full stop or more at some ISO settings - including lower ones.
Some of the downsides to Multi-Shot Noise Reduction include: MSNR is currently available only with JPG output - I want this feature to be added to DPP for RAW capture - perhaps as another HDR preset? Multi-Shot Noise Reduction will not be so useful with moving subjects. Long exposure NR must be off to enable MSNR. The T4i reverts to Standard NR in Basic zone modes, during video recording, in Bulb mode and when the camera is powered off. Flash is not supported in MSNR mode. And the camera remains "busy" for a brief period of time after the 4 shot burst - while processing the merged image.
New with the T4i was the highest-ever-in-a-Canon-APS-C-DSLR ISO setting of 25600. I find this setting is useful for marketing purposes only. But the Canon T5i now has this capability – in case you want to one-up your friends.
ISO 12800 results are not pretty. Even ISO 3200 and above is best avoided on APS-C DSLRs right now, but 3200 and 6400 can be used for extreme situations - or when Multi-Shot Noise Reduction is used.
Here is another noise comparison that includes fine details in a piece of fabric.
The fine details in the fabric better-hide high ISO noise.
Back to the Canon EOS Rebel T5i / 700D Review.