Canon PowerShot G1 X Mark II Review
The actual sensitivity of each indicated ISO is measured using the same shots as are used to measure ISO noise levels, we simply compare the exposure for each shot to the metered light level (using a calibrated Sekonic L-358), middle gray matched. We estimate the accuracy of these results to be +/- 1/6 EV (the margin of error given in the ISO specifications). Note that these tests are based on the sRGB JPEG output of the cameras, in accordance with ISO 12232:2006, the standard used by camera manufacturers. In our tests we found that measured ISOs from the G1 X Mark II are within 1/6 stop of their stated value, so can be considered accurate.
Noise and Noise Reduction (JPEG)
ISO range noise comparison
For the noise test below we've included the PowerShot G1 X (for obvious reasons), the Sony Cyber-shot DSC-RX100 II (being another large-sensor enthusiast compact), and a Canon EOS 700D (Rebel T5i) as an APS-C representative.The G1 X Mark II keeps noise levels relatively low, with the real jump happening at around ISO 6400. If you look at the stamps, it's at that point that detail goes south - meaning it's keeping noise down by applying quite high levels of noise reduction. The Sony RX100 II - which has a more modern 1"-type BSI-CMOS sensor - shows less measured noise than the Canon (a result of higher noise reduction being applied). The G1 X II has considerably less noise than the EOS 700D, which uses similar sensor technology but an older processor. The G1 X II's noise performance is likely to be down to its use of the fairly strong noise reduction introduced in the EOS 5D Mark III. While there has been much talk about the G1 X Mark II being noisier than its predecessor, the difference is actually very small. We wouldn't be surprised to find the two cameras use the same sensor, but with the Mark II making use of a slightly smaller region of it. There are three JPEG noise reduction modes on the G1 X II: standard, low, and high (there is no 'off'). The default, as you might have guessed, is standard. These modes behave exactly are one would expect. The high NR setting has less noise than NR Standard, and so on.
JPEG Dynamic Range/Tone Curve
Our Dynamic Range measurement system involves shooting a calibrated Stouffer Step Wedge (13 stops total range) which is backlit using a daylight balanced lamp (98 CRI). A single shot of this produces a gray scale wedge from the camera's clipped white point down to black (example below). Each step of the scale is equivalent to 1/3 EV (a third of a stop), we select one step as 'middle gray' (defined as 50% luminance) and measure outwards to define the dynamic range. Hence there are 'two sides' to our results, the amount of shadow range (below middle gray) and the amount of highlight range (above middle gray).
To most people highlight range is the first thing they think about when talking about dynamic range, that is the amount of highlight detail above middle gray the camera can capture before it clips to white. Shadow range is more complicated; in our test the line on the graph stops as soon as the luminance value drops below our defined 'black point' (about 2% luminance) or the signal-to-noise ratio drops below a predefined value (where shadow detail would be swamped by noise), whichever comes first.
For our comparison of JPEG dynamic range we're comparing the G1 X Mark II against the Sony Cyber-shot DSC-RX100 II, Olympus E-M10 (as a Micro Four Thirds representative), and the Canon EOS 700D is the APS-C example.
With its DR Correct feature turned off, the G1 X II captures a bit more highlight tone that its predecessor, but the Sony RX100 II wins the day. If you compare just the G1 X II and RX100 II, it appears that the Canon goes deeper into the shadows, but as you'll see on the Image Quality page, noise is already having an impact in that region, and the Sony comes out on top.
The G1 X II has both dynamic range and shadow correction. These are for JPEG shooting only (and are disabled when using Raw+JPEG) and can be used separately or together. DR Correction has four options: off, Auto, 200%, and 400%. Much like Fujifilm cameras, the camera is using three different amplification/tone curve combinations to capture and incorporate more highlight detail.
In order to allow for this extra room for highlight tone, the camera boosts the minimum ISO. For DR 200%, that's ISO 200, and double that for DR 400%. Below you can see how the tone curve changes at the different DR settings:
As you can see, the DR correction feature gives you more information in the highlights, and increasingly smooth roll-off. This comes at the cost of increased noise in the shadows. Because these modes push tones deeper into the camera's Raw response, the shadow regions of each mode become increasingly noisy (as we saw on the Image Quality page, noise is already lurking in the shadows).
As mentioned above, there is also a shadow correction mode, which has options of 'Off' and 'Auto'. Below you can see the effects of those two options:
The Shadow Correct feature does indeed pull up the shadows, by about two stops according to our tests. It also affects midtones, and makes the transition to white more abrupt. It can be combined with the DR Correction modes but this risks making the shadow noise even more visible.
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