Collaboration Overview
2017-12-20 by Bill Claff
The
purpose of this document is to introduce people to the general guidelines for
collaborating in gathering sensor characterization data.
I gather raw image files of several particular styles and perform statistical
analysis on those files to present findings.
Full size raw images are required for the analysis.
Set all noise
reduction settings to off (or a low as possible if off is not an option). In
particular do not use High ISO Noise Reduction.
DR boost if available should be off and any lens corrections disabled if
possible.
The desire is to get as "pure" a raw file as possible.
For Sony
uncompressed is preferred to eliminate any artifacts from the lossy
compression.
If there is both a
mechanical and electronic shutter use the mechanical.
If your camera does
more than one bit depth, such as 14‑bit and 12‑bit then use the
higher bit depth.
You will be using
Manual mode and Manual focus. Make sure Exposure Compensation is 0.
I always test every ISO including any intermediate or extended ones.
On some cameras you will need to change something to enable extended ISO
settings.
If your camera does 1/3 EV settings then change the menu if necessary to allow
that as well.
I have constructed these tests as a compromise between what one might do in a laboratory, with the freedom to take a large number of images and control a number of variables, and what is practical to ask ordinary photographers to provide.
I typically collect three sets of data.
Some
of the images are simply black frames.
Generally these are taken with the lens (or body) cap on and at the highest
shutter speed. (eg. 1/8000s) and smallest aperture (eg. f/22).
Body cap is best because it defeats any lens processing that might occur.
It's also not a bad idea to cover the viewfinder (if there is one) to guard
against light leakage.
Take a single black frame at every ISO setting including extended and intermediate ISOs.
Choose any lens you
like. Probably it will be easier with a short and light lens.
Images
will be taken at the lowest analog ISO.
For most cameras the lowest numbered ISO setting is the lowest analog ISO; but
on some its the next ISO setting up.
When in doubt wait for my feedback based on the Read Noise images.
Simply take 16 black frames as you did for Read Noise (set#1).
Evenly
exposed frames are taken of your computer screen at the same ISO setting as the
black frames.
You will set your lens to infinity focus and place the front of the lens
(filter threads, not you actual lens!) against the computer screen.
Some people prefer to use a tripod, the important thing is that all the images
are as equally exposed as is possible.
This ensures a diffuse image. Because some cameras modify raw data at low
f-numbers I suggest f/4 as a good aperture.
Also, at f-numbers lower than 4 there is often light fall-off that interferes
with the analysis.
A short primes lens is usually a good choice but wide angles lenses are a
problem because they have such a deep Depth Of Field (DOF).
The following image is preferred because it exposes the red and blue channels
more evenly than a simple white image:
You
can also use any other uniform target other than the computer screen but will
need a tripod for consistent images if the lens is not against the screen.
Take 16 of these images.
If
the sensor does dual conversion gain a second set of FPN Black and FPN
Illuminated frames is desirable.
I need to inspect the Read Noise files to determine which ISO setting to use
for this additional data.
Contact me at BClaff@comcast.net to gain
access to my Dropbox to transfer your files or to arrange for an alternate
method.