Here is examined noise from ISO 100 through ISO 6400, plus what Nikon calls ISO L1.0 (50) and Hi-1 and Hi-2 (12800 and 25600).
Be sure to use a colorspace-aware web browser to view the example on this pages, which are in ProPhotoRGB.
Noise and megapixels
An appropriate and meaningful comparison of noise must always be considered in context of the camera megapixels, not an absolute on a per pixel basis. After all, one can downsample the Nikon D800 images to the resolution of the Nikon D3s (12MP) or the Canon 5D Mark III (22MP), etc, and downsampling reduces the appearance of noise.
Choice of color space
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