ISO noise

The comparatively big sensor of the Nikon D5000 indicates an exemplary noise performance due to the low pixel density. Let's compare the results for RAW, JPEG with and without noise reduction and check whether the results meet our expectations.

The chart below shows the results based on a RAW-file analysis:

The Nikon D5000 is a great performer throughout the ISO range. There are no problems at ISO 100, 200,400 as well as ISO 800 and 1600 are also perfectly fine for most scenes. However, at ISO 3200 the noise level is starting to spoil the game, but it's still usable in some situations, while ISO 6400 is definitely out of race.

The next chart shows the results based on a JPEG-file analysis without noise reduction:

Comparing to the RAW output, the JPEG analysis shows nearly the same results, besides the ISO 6400 tuning. However, the high ISO output is still unusable.

And the last chart shows the results based on a JPEG-file analysis with noise reduction:

The JPEG output with noise reduction shows comparatively less noise than the converted RAW files, but the increasing noise reduction towards high ISO settings comes at cost of resolution and dynamic range - specifically at high ISO settings.
These are the lab results, but 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 colour 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):