What a difference a sensor makes. Though the A550 is the same 14.2-megapixel resolution as the cheaper A380, the A550's Exmor CMOS sensor delivers much cleaner images at all ISO sensitivities than the CCD used by its sibling does. They're sharp and relatively clean at least through ISO 400. ISO 800 looks very good on my high-end, color calibrated monitor, but slightly noisy on my cheapo standard-issue display. At ISO 1,600, image detail starts to mush up a bit, but for the most part, detailed photos can remain usable up through ISO 3,200.
As is typical for its class, ISO 6,400 and above are more emergency modes than for everyday shooting; however, the A550 displays better noise suppression at these midrange ISO sensitivities than we usually see from Sony. Its ISO 6,400 shot, for example, is much cleaner than our equivalent shot with the full-frame A900 and A850 models.
Though you have to take this comparison with a grain of salt--I couldn't reshoot the 7D to match because I no longer have the lens so the settings aren't comparable--you can see that the A550's noise at ISO 6,400 fares pretty well compared with the more expensive 7D.
(A550: 1/50 sec, f4.5, multisegment metering, AWB, ISO 6,400, 18-55mm lens at 35mm. 7D: 1/15 sec, f11, pattern metering, AWB, ISO 6,400, 15-85mm lens at 70mm.)
While the original JPEG version of the this shot looked OK, it was slightly underexposed. But it held up surprisingly well to exposure adjustment and color correction. Once again, it looks much better on my high-end, calibrated display than on a typical consumer model.
(1/60 sec, f2.8, ISO 800, multisegment metering, 24-70mm f2.8 ZA SSM lens at 45mm. Raw file processed with Adobe Camera Raw 22.214.171.124; custom white balance, exposure boosted +1, Blacks setting=2, all other defaults.)
Though it's only two shots and takes longer to save to the card than I'd like, Sony's Auto HDR does a decent job of producing images with a larger dynamic range than it would otherwise render. Note that you do gain a little depth of field as well.
(1/50 sec, f4.5, ISO 400, multisegment metering, AWB, 18-55mm lens at 35mm. Top with standard Dynamic Range Optimization, bottom with AutoHDR.)
The lack of any daylit natural colors in new York City in February makes it difficult to show how much Sony pushes the saturation of its colors in its default Standard Creative Style. Worse, with this model it looks like the raw files are similarly oversaturated.
(1/60 sec, f5.6, ISO 200, AWB, pattern metering, Creative Style standard, 18-55mm lens at 50mm, DRO auto)