Compared to...

Studio scene comparison (higher sensitivities)

Nikon's approach to noise reduction has always been chroma (color) noise reduction first, then relatively mild amounts of luminance noise reduction. This tends to leave its high sensitivity images looking more detailed but with potentially more visible luminance 'grain' noise (which isn't generally as objectionable as the more digital-like blotchy color noise). There's no doubt that this approach works very well on the D3X. At higher ISOs it beats the Canon EOS-1Ds Mark III and Sony in terms of visible noise and retained detail and even the highest sensitivity output is still usable, maybe not for a large scale print but certainly for web-use or moderately-sized prints.

For the purpose of this comparison we have also included the new Canon EOS 5D Mark II (at lower sensitivities its output is virtually identical to the EOS-1Ds Mark III), which does a slightly better job at high ISOs than its bigger brother. It's pretty much on par with the D3X showing comparable detail at ISO 1600. At the highest sensitivities Canon's stronger luminance noise reduction results in some blurring of detail, but there's also visibly less grain than in the D3X image, giving a more appealing overall result.

At equal viewing size the D3X does an admirable job against our current high ISO benchmark, the D3, showing slightly more luminance noise but also retaining very good detail. However, while the D3X's ISO scale ends at 6400 you can push the D3 up to 25600, so if you tend to shoot in almost complete darkness you don't have too much choice.

ISO 1600

Nikon D3X Canon EOS-1Ds Mark III
Sony DSLR-A900 Nikon D3
Canon EOS 5D Mark II  

ISO 3200

Nikon D3X Canon EOS-1Ds Mark III
Sony DSLR-A900 Nikon D3
Canon EOS 5D Mark II  

ISO 6400

Nikon D3X Sony DSLR-A900
Canon EOS 5D Mark II Nikon D3

D3 at equal viewing size

For this comparison we have downsized the D3X's 24.5 MP images to the same size as the D3's 12MP output using 'Bicubic' resampling in Adobe Photoshop. As you see, the downsized D3X images show slightly more detail (and quite a lot more sharpness) but also slightly more luminance noise (grain). All in all though, at equal output size, there is not an awful lot of difference. However, while the D3X gives up at ISO 6400 you can increase sensitivity on a D3 up to 25600, and keep shooting in near darkness.

Nikon D3X - ISO 1600 downsized Nikon D3 - ISO 1600
Nikon D3X - ISO 3200 downsized Nikon D3 - ISO 3200
Nikon D3X - ISO 6400 downsized Nikon D3 - ISO 6400