ISO noise

Let's have a look at the results of Sonys' 23.4 x 15.6 mm CMOS sensor with respect to the ISO performance. Based on converted RAW files the Sony A550 is generally a good performer throughout the ISO range. There are no problems at ISO 100/200 and ISO 400 as well as ISO 800 are also perfectly fine for most scenes. However, at ISO 1600 and more so at ISO 3200 the noise level is starting to have a higher impact but they may be still usable at times, while ISO 6400 and 12800 are nothing but gimmicks.

Unfortunately, the A550 doesn't provide sufficient control about noise reduction in JPEG mode; you can't turn it off and only switch between standard and high and this is why the next chart shows the results based on a JPEG-file analysis only with standard noise reduction:

Comparing to the RAW output, the JPEG analysis shows different results. The JPEG output with standard noise reduction shows comparatively less noise than the converted RAW files but as already mentioned at cost of resolution. However, these are the lab results and I guess you're also interested in some samples taken in the real world. The first image series should give you an idea of the color noise at the specific settings.

... and another series with a more detailed subject.

	low ISO noise (ISO 100-200):
	mid ISO noise (ISO 400-800):
	high ISO noise (ISO 1600-3200):