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Brief test: Canon PowerShot A630 vs A640 noise and outdoor detail

The Canon PowerShot A630 and A640 were announced alongside each other in August 2006 and replace the popular A610 and A620 models. Like their predecessors, the biggest difference between the new models is resolution: 8 Megapixels on the A630 and 10 Megapixels on the A640. The A640 may also come with bigger memory card, support for remote capture through software control, and a black finish, but the sensor is the main difference.

  Canon PowerShot A640

So the question facing potential buyers of either camera is whether the extra 2 Megapixels of the A640 are worth having? Do the A640's images contain noticeably greater detail in real life? And are noise levels at higher sensitivities better on the A630 thanks to its lower resolution?

To answer these questions we got hold of both the A630 and A640 and photographed the same scene moments apart using each of their ISO settings and have presented the results below. This page illustrates the main difference between the A630 and A640, but if you'd like to find out more about their operation, control and optical quality, check out our Canon PowerShot A640 review. The review may concentrate on the A640, but since the body, battery, lens and screen are identical to the A630, the results and discussions equally apply to both models. But for now, back to our brief PowerShot head-to-head.

To compare resolving power and noise levels under real-life conditions we shot the same scene using the Canon PowerShot A630 and PowerShot A640 within a few moments of each other using their best quality JPEG options, and at each ISO setting.

The lenses on both cameras here were adjusted to deliver identical fields of view. Due to the high brightness of the scene and requirement to shoot it at up to 800 ISO, we were forced to shoot in Aperture Priority at f6.3. Our Canon A640 review showed the lens employed by both it and the A630 can deliver a slightly sharper result opened to f4.5, but the f6.3 setting we had to use here is only fractionally behind.

The image above was taken with the Canon PowerShot A630 at 22mm f6.3 and at 100 ISO; the original measured 2.12MB. The crops are taken from an area below and to the left of center and shown here at 100%. The A630 samples shows a larger area due to its lower resolution sensor.

Note: we have compared 100% crops from each camera here measuring 136x282 pixels. Since the A640 employs a higher resolution sensor, its crops represent a smaller area of the total image size than the A630 crops. As such, any artefacts seen on the A640 crops below would appear slightly smaller than those on the other crops if the original images were printed exactly the same size.

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Canon PowerShot A630
Canon PowerShot A640
Canon A630 at 80 ISO
Canon A640 at 80 ISO
80 ISO, 1/160, f6.3
80 ISO, 1/160, f6.3
Canon A630 at 100 ISO
Canon A640 at 100 ISO
100 ISO, 1/250, f6.3
100 ISO, 1/250, f6.3
Canon A630 at 200 ISO
Canon A640 at 200 ISO
200 ISO, 1/500, f6.3
200 ISO, 1/500, f6.3
Canon A630 at 400 ISO
Canon A640 at 400 ISO
400 ISO, 1/1000, f6.3
400 ISO, 1/1000, f6.3
Canon A630 at 800 ISO
Canon A640 at 800 ISO
800 ISO, 1/2000, f6.3
800 ISO, 1/2000, f6.3

From the crops above, it's clear the A640 resolves slightly greater detail than the A630. It's not a huge difference, but the A640 samples more clearly separate the vertical bars in the fenced area, along with better resolving the antennas and their supports. It's subtle, but there's certainly a slight resolution advantage to the A640.

This result was expected, but the comparative noise levels came as a surprise. Both cameras deliver clean smooth results at 80 ISO as you'd expect, but at 100 and 200 ISO one camera exhibits more noticeable noise speckles in areas of flat colour like the background walls and the blue rooftop; the big surprise is the higher noise levels are seen on the A630 samples.

At 400 and 800 ISO these differences become more obvious, and while both cameras exhibit greater noise levels than we'd like to see, they're visibly higher on the A630. Interestingly even if the A640 were applying greater noise reduction, this hasn't compromised fine detail like the antenna masts, which are much better defined on the 800 ISO sample than the A630. And remember since the A640 crops represent a smaller area of the total image, the noise artefacts you see in the crops above appear slightly smaller than those on the A630 if each complete image were printed the same size.

This is a surprising result since both cameras have sensors which physically measure the same size, so by sporting higher resolution, the actual sensitive pixel areas on the A640 are smaller than those on the A630. So common sense tells us it should also exhibit higher noise.

click here for the Canon A640 video tour

Of course there are many other factors to consider in practice. The A640's sensor may pack in more pixels, but it might make more efficient use of the gaps between them. Then there's the whole amplification and processing chain which brings you the final image.

The bottom line though is the A640 doesn't only deliver slightly higher resolution images, but also appears to do so with lower noise than the A630. Again it's a pretty subtle difference, but from the results above, you certainly shouldn't be concerned of compromised noise levels if you opt for the 10 Megapixel PowerShot A640 over the 8 Megapixel A630. For full details of the A640 design, operation, menus and optical results, along with a video tour, please visit our Canon PowerShot A640 review.

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All words, images, videos and layout, copyright 2005-2014 Gordon Laing. May not be used without permission.

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