Shadow noise

The Nikon D7000's imaging sensor is of a new generation which produces exceptionally low read noise at base ISO. This lowers the noise floor that usually limits DR and means that you can pull much more dynamic range out of the shadows in RAW conversion than with 'conventional' sensors.

To illustrate this we have taken the base ISO RAW shots of our studio test scene and developed them in Adobe Camera RAW with a +3.0EV digital exposure compensation to lift the shadows. We've then taken crops in the darkest areas of our scene to compare the level of shadow noise on the D7000 and the Canon EOS 60D which features a more conventional imaging sensor. Applying the digital exposure compensation makes shadow noise more visible and at 100% magnification it becomes clear that the Nikon D7000 produces noticeably less shadow noise than the Canon. Take a look at the sample shot below to see how this low shadow noise translates into a real-life advantage.

Nikon D7000 - ACR+3.0EV Canon EOS 60D - ACR+3.0EV
100% crop 100% crop
100% crop 100% crop

In real life this means that, due to the exceptionally low shadow noise in the D7000 output, the shadows in a scene can be lifted in RAW conversion to create a high dynamic range image without sacrificing highlight detail or getting excessive noise in the shadows. To illustrate this we've produced four different images of the same scene. The first image is the metered exposure which, at a shutter speed of 1/50 sec has blown highlights. The second image was taken with a 3.0EV negative exposure compensation. This helped to protect the highlights but blocked up the shadows at 1/200 sec.

We've then taken the RAW file of the underexposed image and lifted the shadows areas in Adobe Camera RAW. In order to do this we increased a range of parameters including recovery, fill-light and brightness. and reduced the blacks. The results is a version of our underexposed image that pulls up the shadows a couple of stops while retaining the highlights. However, the image looks rather flat with low contrast. To convert it into a more 'life-like' image with normal contrast we've done some more post processing and produced a second ACR conversion. It's similar to the first version but we have additionally applied a touch of perspective correction in the raw conversion, a masked curves adjustment layer to boost the overall contrast and a masked warm-up filter.

This little exercise shows two things: firstly you can pull a lot of dynamic range out of a D7000 file, and secondly it does take quite a bit of extra work to put all this extra tonal information into an image file that looks reasonable.

JPEG - metered exposure JPEG - metered exposure -3.0EV
ACR conversion 1 ACR conversion 2

The 100% crops below give you a better idea of the results. In the metered exposure a lot of the highlights in the sky and on some of the buildings have blown out and detail has been lost. On the plus side there is still some detail in the dark areas of the foliage towards the bottom right of the frame. When we captured the same scene with a negative exposure compensation of 3.0EV we managed to protect the highlights but there is very little detail left in the shadow areas.

In our Adobe Camera RAW conversion we've been able to lift the shadows and significantly increase the shadow detail without sacrificing the highlights or increasing the shadow noise. In the second ACR conversion we have applied additional post processing steps to get closer to a ‘finished’ file of normal contrast but the highlight and shadow detail of the previous conversion have been maintained.

JPEG - metered exposure - 100% crop
JPEG - metered exposure -3.0EV - 100% crop
ACR conversion 1 - 100% crop
ACR conversion 2 - 100% crop

Active D-lighting has been a standard feature on Nikon DSLRs for a while now. The system modifies metering and adjusts contrast at a local level in order to maximize the amount of dynamic range information squeezed into the JPEG file. A positive 'side-effect' of the increased shadow noise levels of the new sensor is that high A-DL settings are now much less likely to introduce noise into the shadow areas of the JPEG output. See the examples below for a comparison between the A-DL 'Off' and 'Extra High' settings.

A-DL Off A-DL Extra High
100% crops - Highlight area
100% crops - Shadow area