Canon Powershot G11 Review

Noise

The problem with small sensor digicams is, well...they have small sensors. The G11 sensor is on the large end of the range for digicams, and it's only 7.6 x 5.7mm. Now when you put 10 million pixels (10MP) on such a sensor, the pixels are small. Really small. The pixel size (pitch) on the Powershot G10 (14.7MP) was 1.7 microns and on the G11 (10MP) it is 2,1 microns (a micron is 1 millionth of a meter, or 1/1000 of a mm). The problem with small pixels is that they generate more noise then larger pixels for a given signal level and of course this results in image noise.

By going to fewer (and therefore larger) pixels with the G11, as well as using the Digic IV imaging engine, Canon have lowered the noise level compared to that of the G10. It's hard to exactly quantify the improvement, but it's probably between 1 and two stops, so the G11 at ISO 1600 beats the G10 at ISO 800.

High ISO settings make noise worse of course and so all digicam manufacturers utilize some pretty aggressive digital noise reduction algorithms to make the images look better. Unfortunately a side effect of noise reduction is resolution reduction. The images get softer. In the limit where noise is so bad that very high levels of noise reduction is required, the images don't just go soft, they can turn quite nasty, looking more like a watercolor painting than a photograph.

So how well have Canon done with the G11?

First let's look at some resolution test shots at various ISO settings. I haven't included ISO 80 in order to save a little space. It looks much like ISO 100, but maybe just slightly better!

The most obvious effect is the blurring of detail at ISO 1600 and especially ISO 3200. The noise reduction algorithms have reduced noise, but they have blurred the images. At ISO 800 things look better. Yes, there's some noise but sharpness holds up pretty well. Moving to ISO 400 things now look quite good. sharpness is up along with contrast. At ISO 200, 100 and ISO 80 things look great, as good as most DSLRs in terms of both noise and resolution.

Looking at some color patches we can see much the same thing:

Again ISO 80 has been left out to save space. It looks pretty much like ISO 100.

So how does the G11 compare to other digicams and SLRs? Well, below is a comparison of sections of a test image shot with a Powershot A720is (8MP), a Powershot G11 (10MP) and an EOS 50D (15MP), all at ISO 1600.

It's pretty clear that the G11 can't match the EOS 50D (which has a sensor which has 7.6x more area), but it's a good deal better than the A720.

Low Light Mode

In the Low Light program mode the G11 reduces to image size to a medium JPEG (RAW is not possible) which has 2.5MP rather than the 10MP of the full sensor. Presumably the full 10MP is recorded and then downsized to 2.5MP by averaging pixels (which lowers noise). In this mode the ISO is set automatically between ISO 320 and ISO 12800, but biased toward high ISO and fast shutter speeds. When the normal program mode selects ISO 800, the Low Light mode might select ISO 3200. The idea is to keep shutter speed high so that the image is sharper. In fact the shutter speed won't go below 1/15s. If the lens is wide open, the ISO is 12800 and the required shutter speed is slower than 1/15s, the image will just be shot at 1/15s and it will be underexposed.

At moderate ISO boost the images are quite usable for the web, maybe even small prints. Below is a sample shot in Low Light mode at ISO 4000. It doesn't look bad here.

The next image shows the difference between the Program mode and Low light mode. These two shots were taken a few seconds apart.

Clearly I think you want to leave Low Light mode as a last resort, using the regular program mode and ISO 3200 while the shutter speed is fast enough to be able to steady the camera. This shot was handheld at 1/8s in program mode, which shows the effectiveness of the image stabilization (the lens was zoomed to 13.8mm (equal to about 64mm in 35mm equivalent terms).

Finally of course, things fall apart if the light level drops enough. Here's an example of where low light mode used ISO 10000. It's not pretty.

Things are bad enough at ISO 3200. At ISO 10000 they're pretty horrible.

NEXT: Conclusions