Imaging Resource and DPReview have sample images up for the Canon EOS 70D. These are still considered pre-production, as the camera won't ship until September '13. However, there is enough information in these shots to get a general feel of how the 70D's sensor and JPEG picture engine will work relative to other more known quantities... especially it's predecessor the EOS 60D and perhaps it's most direct competitor, the Nikon D7100. Because its novel approach to autofocus, interest remains high in how this sensor will perform, and as per usual, that means browsing through lots of ISO samples. Pixel peeping after the jump.
For reference, here are the links to IR's sample images, referencing the middle of the road samples whenver possible (neutral nosie reduction, etc)
The 70D's output resolution is 5472 x 3648 for a total of just under 20mp. However, unlike the Nikon D7100, it stays with an optical low-pass filter, meaning that the real amount of resolution captured by the sensor won't be as close to the theoretical maximum as with an filterless sensor.
Using the 60D as a reference, IR reported strong detail to 2,100 horizontal lines and 2,000 vertical lines, with extinction occurring above 3,000 lines. Just as a note, Imaging-Resource is fairly conservative with their interpretation of resolution charts. At 5,184 × 3,456 output, this is well short of the camera's Nyquist frequency (theoretical maximum resolution capture). By comparison, DPReview reports a similar, but higher value of 2500 lines per picture height. To put the difference between the two sites in perspective, IR reported 2,600 lph for the D7100. This is just numerical interpretation, though, different ways of quantifying the same visual image.
Using the same criteria that IR used for interpreting the 60D's resolution tests, I would say that the 70D would fall into the range of 2,200 horizontal and 2,100 vertical strongly resolved lines. In other words, not a lot of change compared to the EOS 60D. As a general rule of thumb, it takes an improvement of 10% in linear resolution to be discernable under normal viewing. However, this is largely irrelevant, as the older 18mp sensor didn't suffer for lack of resolution, and you would have to move up significantly in pixel count (to something like the Nikon D800) to print at the same quality when moving up in print sizes as well.
As per usual, rather than commenting on the whole gamut of the ISO range, I'll comment on the key areas of the transition zone when noise starts becoming an issue for more than casual snapshots. That's usually between ISO 1600 and 3200 on an APS-C camera; above this, quality results can be achievable, but with much more mindful shooting and more time spent post-processing. (Reminder, Imaging-Resource's test charts are from the out-of-camera JPEG's.)
There's not much to separate the 70D from the 60D. Both cameras produce images that have a "family resemblance", and at ISO 100, you would be hard pressed to describe any meaningful differences. The 70D seems to have a bit more dynamic range; if you look at the blacks, they seem to have just a few more "shades of black" than in the 60D. The 70D also seems to have a slight bit more colour saturation; however, differences can be due to lighting variations and tweaks in camera settings.
However, there is a tangible difference between these two cameras and the Nikon D7100; the extra resolving power from a combined advantage and pixel count and lack of anti-aliasing filter make for visibly more detailed samples. As I described before... sometimes the difference with the D7100 is not much, but it is noticeable. Hard details are more contrasty and low contrast details stand out a bit more. Bear in minds, this is the kind of resolution advantage that can easily be wiped out by natural hand movements. Note also that the D7100 also picks out the texture of the wall behind the still life subject quite well.
Even though, ISO 800 is still a usable ISO level, there is noticeable image quality degradation is you know where to look for it. First off, though, the 70D samples appears a bit softer than the 60D; I wouldn't read to much into that because there's often a bit of variation in focus with test subjects like this. A difference of a few mm can make one sample look softer than another, but in real-world terms, it's not significant. The second caveat is that the 70D is pre-production; as far as I can see, the samples seem to have more chroma noise when the exposure drops off. By comparison, you can also make out chroma noise in the D7100, but the texture is much finer. The third caveat is that you have to view the images at the same magnification to fairly compare image noise levels.
In general, I would say that all three cameras start loosing fine details in areas with broad patches of reds and blues, but the D7100 is holding onto the fine detail better. In the deepest shadows, you can just start to make out what would eventually be banding if you pushed the exposure further in post-processing; the noise pattern out of camera is not "banded", but if you look long enough, you can see that the grain of the noise in the Nikon, though even, looks just a little more orderly than it does with the Canon's.
Though all are usable, even without major corrective processing, at 100% none of these images are what I would consider to be "great." It would be prudent to crop as little as possible into ISO 1600 images from these cameras, as that would magnify the noise relative to the size of the image. Both the 70D and the D7100 show higher levels of subjective image noise than the 70D, though both do so with a different quality of texture. The D7100 is the nosiest of the three, but also still retains the most detail.
This is as high as I would want to go with all three cameras in normal usage. The grain of the noise is quite visible. Once again, the D7100 shows the most texture and detail preservation in the reds thanks to the lack of the AA filter, but paradoxically, it also shows the most loss in edge definition with hard lines because of image noise. In terms of edge definition, the 60D seems to edge out the 70D, though not by much. Chroma noise is more splotchy in the 70D than it is in the 60D. Once again; though I wouldn't go so far as to call it banding; you can make out an increased orderliness to the pattern noise in the deep blacks of the D7100 sample, though in fairness, you can see the same phenomenon in the deep blacks of the 70D sample as well.
Not much to see here folks. At high ISO, even when noise reduction is "turned-off", it's not really off. The differences that you see here are more down to how each camera is managing the noise rather than to the innate properties of the sensor itself. The 60D looks the worst off; I'm attributing that to the fact that it's the oldest camera here, meaning that it's hard-coded noise-reduction algorithms are also the oldest. The 70D has the most chroma noise, and looks like it could use more tuning before the camera is finalized. In a reversal of trends, the D7100 looks the smoothest, but obviously has more noise reduction applied.
Same trends apply, but going through the ISO range, the DPR samples show an improvement of the 70D over the 60D at every ISO level in how the noise is handled. I wouldn't necessarily call it a cleaner sensor; it's more a case that the noise is handled better. Indeed, if you flip to DPR's ACR RAW samples, there doesn't appear to be much significant different between the two.
It simply wouldn't be fair to draw conclusions about the 70D's still image quality while they are in pre-production, as the samples do indicate that there is room for improvement. However, it's almost enough to say that there's no real world different between the 60D and the 70D, which is a mixed blessing. In terms of real-world shooting, the added resolution of the D7100 would take extra work to extract, so even the 60D remains usable and relevant in today's market. However, the advanced Canon enthusiasts have been quite vocal about the lack of progress in sensor technology, and these results won't really help matters.
As discussed in a previous post, the way the image-pipeline is arranged in the 70D (and all Canon DSLR's) means that it will not be able to achieve the ultra-clean low ISO image quality of the Sony 16mp sensor found in the Nikon D7000 and NEX-6. However, there are advantages to video and astrophotography applications. To put this in context, though, the 70D sensor is like a 20mp sensor's filter array sitting on top of a 40mp sensor's substrate bed. Because the phase-detection autofocus capability extends to every photodiode, the number of wiring interconnects is significantly higher than in a competing sensor. Even to achieve the same image quality as its predecessor is an achievement under these circumstances.
Increasingly, I'm seeing the 70D not as a competitor to the D7100 or even the D7000, but as what the Nikon D5200 should be for the all-around "advanced casual" user. The Nikon almost gets it right extending its video capabilities with a flip-out LCD screen, but it falls short in having truly usable autofocus. If the 70D lives up to it's promise of improved motion tracking autofocus in live-view, then it will be a very competitive non-pro cinematographer's camera. Maybe even pro. Shooting a wedding? The 5DmII and 5DmIII will produce dreamy cinematography with their ability to produce shallow depth of field, but the 70D could potentially be the best fuss-free on-the-go candid documentary device.
For those of you holding out for an eventual/possible 7DmII, these results are actually somewhat re-assuring. The 70D, for all of it's phase detection autofocus trickery, doesn't really move the game forward in terms of still quality. What is acceptable and appropriate for the 70D isn't so for the 7D series; if anything, Canon have left themselves room for a more stills-oriented sensor/image-pipeline in keeping with the action photographer leanings of the 7D series.
Final note: A word of appreciation to IR and DPR. All too often, the enthusiast community takes their sample test shots for granted, but producing consistent test sample is not small feat.