Read Noise
Collaboration
Prepared 2007-12-10 by Bill Claff
The purpose of the collaboration is to collect read noise information on all Nikon DSLR models.
Read noise is the major component that limits sensor
performance.
We can also measure Photo Response Non-Uniformity (PRNU) and the noise floor
with the same set of measurements.
In practical terms it is this combination of factors that truly limits
performance.
A rigorous approach requires numerous pairs of exposures
taken at different low light intensities.
However, this expedited procedure uses
a smaller number of pairs to produce reasonable results.
You need to be
running a Windows system and to get the following from my web site:
(You should be able to right‑click and save from these links.)
Place them all in
the same directory.
Choose your fastest
lens that can take images of your computer monitor at a comfortable distance.
Use a 50mm f/1.8D AF-Nikkor if it is available as this is what I used to
collect my data.
Use default noise
reduction settings. In particular do not use long exposure noise reduction.
Do not use ISO Auto.
Use RAW or RAW+JPG.
If your camera does
both 14‑bit and 12‑bit then use 14‑bit.
You will be using
Manual mode and Manual focus. Be certain Exposure Compensation is set to 0.
Using a ‘DOS box’
run the flat_target program with parameters as follows:
RN_grid 5 200
Note the intensity
value after the ‘@’ in the program caption. It is initially 200.
The ‘a’ or ‘-‘ keys will reduce the gray value by 5 on each keypress.
The ‘z’ or ‘+’ keys will increase the gray value by 5 on each keypress.
All readings and
images are taken wide open in manual focus with the lens set to infinity and
touching the computer screen.
(If your screen curves a lot then be sure to use a lens with a recessed from
element.)
At this first screen
adjust your monitor brightness so you are properly exposed at 1/30s with the
lens wide open and at the lowest ISO for your camera (even Lo 1.0).
Take 7 pairs of
images at intensities of 85, 90, 95, 100, 105, 110, and 115.
Remember the ‘a‘ and ‘z’ keys will change the intensity value.
Take a set of 14
images (7 pairs) at each full ISO such as Lo 1.0, 100, 200, 400, 800, 1600,
3200, Hi 1.0 etc.
As you increase ISO you can either decreasing shutter duration or stop down to
maintain the same overall exposure.
Transfer the images
into the directory with the downloaded programs and batch file using your usual
procedure (although a card reader is preferred to Nikon Transfer).
Using a ‘DOS box’ in
the directory with the images run the gain_gather batch file.
gain_gather will use
gain_gather1 which will in turn use gain_analyse to extract information from
the NEF files in the directory.
A summary file
called ‘gain.txt’ is also created.
Using a ‘DOS box’ in
the directory with the images run the RN_gather batch file.
RN_gather will use
RN_analyse to extract information from the NEF files in the directory.
A summary file
called ‘RN.txt’ is also created.
Simply e‑mail
the gain.txt and RN.txt files to me at BClaff@comcast.net
and I’ll add your data to the collection.