The Canon Ixus 870 IS has the difficult task of following the Ixus 860 IS, one of the manufacturer's all-time best-sellers.

To face up the job, this new version has a new, bigger sensor with more Megapixels and uses the new DIGIC 4 processor for image treatment.

Along the way, Canon has also tweaked the interface and styling--but is this really a worthy successor?

Handling

On the outside, there's the same mix of metal and plastic, which gives a good grip.

What's changed rather than the materials involved, Canon has honed the dimensions, skimming 2 mm off the 870 in all directions.

In turn, this has involved moving the position of some of the buttons, and they now take up a little more room with out getting the way.

Indeed, all of the controls are easy to use, and our only real criticism is the plasticky feel of the zoom.

On the back, a scroll wheel (as used on Canon's 970 and 980 IS), makes navigating through the menus easy.

While it's a nice addition, it would have been great if Canon had managed to improve the LCD screen, too: the 230 000 pixel three-inch display is perfectly fine and provides fluid images, but could certainly be improved, as other manufacturers have shown.

The new DIGIC 4 processor mentioned in the introduction makes its presence felt most clearly in terms of how responsive the camera now is.

It takes less than a second to power up and just 0.6 seconds for the autofocus to work.

Unfortunately, however, burst mode is rather slow at just 1.5 frames per second, but that's still twice as fast as it was on the 860 IS.
Image Quality

The 870 has an extra two million pixels on its predecessor, which seems like a reasonable adjustment on Canon's part given the waves of 12 MP digital compacts that we've seen recently.

Overall, the extra pixels are worthwhile, and the camera takes great photos at the lowest film speeds (80 and 100 ISO).

Noise is usually under control, although things are a little worse above 800 ISO, although shots here are hardly unusable. 

The new 4x zoom lens, however, is a little disappointing--compared to those on the Panasonic FX37 or even the Ixus 860 IS, none of our test photos were particularly sharp, and there was a definite blurriness along the left edge of the frame.

White balancing is done well and is even, but some colors tend to be too saturated; reds in particular were badly affected we found.

As for video, the main change is a switch of file format, which is now .mov using a H.264 encoding.

This is handled natively in Mac OS X, but is less well-known to Windows users and might prompt some confusion in popular software like Movie Maker.

More troubling is the lack of High Definition video, which is becoming ever more standard and whose absence is difficult to justify.