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White Balance

The SD550 has five white balance presets (sunny, cloudy, incandescent, fluorescent and fluorescent H) in addition to the default auto white balance. There is also a 'custom' white balance setting, which allows you to point the camera at a white or gray object and set the white balance manually. The custom white balance setting is remembered even if you turn the camera off. In normal outdoor shooting the auto white balance works perfectly (as confirmed by our studio tests). Indoors it's a bit more hit and miss, as we've seen with most Canon PowerShots, fluorescent lighting doesn't cause much of a problem, whereas incandescent (tungsten) lighting causes a fairly strong orange color cast (though oddly the SD550 produced a much more neutral result than the SD500... go figure). We've spoken to Canon about its approach to white balance and have been told that the warm colors we see when shooting under incandescent light are intentional and are intended to 'try to keep some of the warm atmosphere of this kind of shot'.

Outdoor - Auto WB
Red -0.4%, Blue -0.7%
Excellent

Fluorescent - Auto WB
Red 0.3%, Blue 0.3%
Excellent
Incandescent - Auto WB
Red 1.3%, Blue -2.7%
Good

Flash Performance

The SD550's built-in flash has a quoted working range of 0.5m - 4.8m (1.6 - 16.4 ft) at the wide end of the zoom and 0.5m - 2.8m (1.6 - 9.8 ft) at the tele end - slightly more powerful than most other models in the range. It also works down to about 30cm (12 inches) in macro mode (in all cases assuming the ISO is set to auto). In our real-world tests the flash did a decent job with a very slight warm tone (which is nice). The flash is also very fast - even with the red-eye reduction turned on, meaning you won't miss any spur of the moment shots waiting for the flash. We found the AF illuminator would allow focus in complete darkness (or as near as we can get) at distances of up to around 1.0m. In low light the AF illuminator can help focus at distances of up to around 2.0m. Incidentally, as our test shot shows, using the red-eye-reduction mode has little - if any - effect.

Skin tone
Very slight underexposure, excellent color
Color chart
Slight underexposure, excellent color

Macro Focus

As is common to most compact digital cameras the SD550's macro mode is most effective at the wide end of the zoom, where you can get as close as 5cm - not bad at all for an 'ultra-compact'. At the long end of the zoom the performance is less impressive - 30cm subject distance - but still pretty useful. There is inevitably some distortion when shooting very close up at the wide end, but it is not too strong, and certainly less so than many of its competitors.

Wide macro - 53 x 40mm coverage
48 px/mm (1226 px/in)
Distortion: Average
Corner softness: Average
Equiv. focal length: 37 mm
Mid Zoom macro - 106 x 79 mm coverage
24 px/mm (620 px/in)
Distortion: Low
Corner softness: Average
Equiv. focal length: 111 mm

Barrel and Pincushion Distortion

Barrel distortion is - at 1.0% - about average for a camera in this class, and certainly doesn't mar real world scenic shots. There is virtually no measurable distortion at the telephoto end of the zoom. There is a tiny amount of vignetting (darkening of the corners of the frame) at the widest zoom setting, but didn't see this in real world shots.

Barrel distortion - 1.0% at Wide angle
Equiv. focal length: 37 mm
Pincushion distortion - 0.1% at Telephoto
Equiv. focal length: 111 mm

Specific Image Quality Issues

Of course all ultra-compact cameras such as this are going to present some kind of compromise when it comes to image quality. The question is how much of a compromise are we prepared to accept in image quality terms to get a camera that is truly pocket-sized, and is there any real advantage to the large 7 megapixel files (over, say the 4 megapixel SD300) in real terms for everyday use?

First the good news; this is a Canon and has all the usual Canon trademarks; excellent, vivid but natural color, very accurate exposure and focus and a surprising amount of detail (see resolution tests). The images - especially those containing fine low contrast detail such as foliage - can look a little soft, or even muddy (they are very smooth, almost too 'polished'), but they respond well to sharpening and print beautifully. Higher contrast detail is rendered very sharply, but very bright, contrasty scenes can cause metering problems - and the fairly high contrast can produce some highlight clipping, but overall there's little to complain about. Finally, as with all other Canon compacts, we found the 'intelligent' AiAF system to be the cause of so many focus errors (and slow focusing in general) that, again, we'd recommend turning it off unless you really can't use the pre-focus (half-press) lock for off-center subjects.

We found corner softness to be a minor problem at the wide end of the zoom/max aperture, but it's a lot better than in previous models, and isn't really visible in real-world shots. We also found the usual Canon Achilles heel, purple fringing, to be a problem in many high contrast shots. Ultimately, the SD550 produces the kind of results few of the target market would find anything to complain about, and it would make a perfect 'carry always' camera for anyone who normally uses a bigger, more sophisticated camera and doesn't want to sacrifice too much image quality for the sake of portability. I'd also note that the problems below represent no more than around 5% of the 400 or so shots I took during this test, and - aside from purple fringing - are confined to a relatively narrow band of shooting situations.

Color fringing

Noticeable purple fringing is present to some degree in most shots containing very bright (especially overexposed) areas, and in some shots it's very pronounced. It's not enough to mar shots in most circumstances, but wideangle shots on bright days can produce very strong fringes at the boundaries where bright and dark areas meet. It is considerably worse at the edge of the frame, and - compact point and shoot camera or not - something Canon should be doing more to minimize.

100% crop 37 mm equiv., F2.8

Clipped highlights / exposure problems

As with the SD500 before it, we found the SD550 occasionally gave us problems in very bright (and especially contrasty) shooting situations, with clipped (blown) highlights not uncommon. The problem (which is by no means unique to this camera) appears to be partly the result of a fairly high default contrast setting (which is common in cameras in the 'lifestyle' sector of the market as it produces 'punchy' prints) and partly due to the metering - sometimes - being fooled by scenes with a very wide range of brightness levels. On occasion in these situations the SD550 has a slight tendency towards overexposure, blowing out the brighter areas. Thankfully in most everyday shots this isn't a serious issue.

100% crop 37 mm equiv., F2.8
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