Overall, noise levels appear higher on the A640 than the other cameras here. They're already visibly worse at 200 ISO and much more so at 400 and 800 ISO. At first this looks like a poor result for the A640, but it actually reveals the camera's relatively modest approach to noise reduction.
Many cameras apply aggressive noise reduction which may hide the noise speckles, but at the cost of smearing fine detail. In contrast, the A640 appears turn down its noise reduction with the result of far more noticeable speckles, but a decent level of detail left intact - you can better see this on the next page. Which approach is preferable is entirely personal, but at least Canon allows you to apply additional noise reduction after the event if desired using software like Noise Ninja.
As always though, the flat colours of the Gretag chart here can hide a multitude of sins, so always additionally compare ISO performance on real-life outdoor subjects as illustrated on the following page and in our Canon A640 Gallery.
Note: we have compared 100% crops from each camera here measuring 136x136 pixels. Since the Canon A640 and Sony N2 employ higher resolution sensors, these crops represent a smaller area of their total image size than the Fujifilm F30 and Panasonic TZ1. As such, any artefacts seen on the Canon A640 and Sony N2 crops would appear smaller than those on the other crops if the original images were printed exactly the same size.