

Noise, Dynamic Range and Bit Depth in Digital SLRs - akkartik
http://theory.uchicago.edu/~ejm/pix/20d/tests/noise

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ChuckMcM
Oooh, thanks for that. I had read it a long time ago and lost track of it. Now
I've added it to my Evernote notebook :-)

Back in the stone age I was a lowly systems guy at the Image Processing
Institute at USC and we spent a lot of resources computing all of the noise
contributors to a digital camera system. The two uses were creating better
cameras (that could compensate for their electronics) and identifying which
images came from which camera (which could be used in authenticating an images
veracity). These days there is so much post processing done in the camera body
I doubt the pattern noise signature can be extracted from an image.

~~~
flywheel
I've been using digital cameras since the first wave of them was introduced in
the 90's.

Since the start I was making hot pixel maps and that helped fix images using
them as a mask in photoshop to reverse the errors caused by hot pixels and
non-random noise.

A hot pixel map is simply a long-exposure photo taken that is completely black
- with the lens cap on, or the lens otherwise blocked from all light.

I've found that as the sensor ages, the "hot" pixels get "hotter". I take a
new pixel map every six months to a year, and have observed the increase in
non-random noise.

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jwise0
One of the interesting things that's changed some since that article was
written has been the advent of truly itsy-bitsy sensors, for instance on cell
phone cameras. Sony, OmniVision, and Aptina are all making sensors on the
scale of 1/3", with pixel sizes as small as 1.1µm; the upshot of this is that
the electrons wells for these pixels are fantastically tiny, and saturate well
below 2,000 electrons.

This means that even on a bright, sunny day, with brilliant opportunities to
pour light into the sensor while maintaining short exposure times, we /still/
can't get as much light in as we want, because if we do, we'll saturate the
pixels -- and no amount of lowering the analog gain in the readout circuitry
will recover the electrons that spilled out of the wells. So, we end up with
shot noise as a dominating factor for cell phone images, even in "perfect"
conditions.

As we cram more pixels into sensors, noise reduction -- in many different
modes -- will become an important battleground in which image sensor and SoC
vendors will have to compete. Glad to see it getting some attention :-)

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ScottBurson
The TL;DR is a little surprising:

First, try to maximize the number of photons collected, by using the largest
aperture and slowest shutter that shooting conditions permit. (This isn't the
surprising part.)

In photon-rich conditions, sensitivity ("ISO") doesn't matter much. In photon-
poor conditions, however -- perhaps you want a small aperture to expand depth-
of-field, or a fast shutter to freeze motion -- you get the best noise
performance by using the _highest_ sensitivity that doesn't saturate
highlights. (This is the surprising part.)

Oh, and there's no point to 14-bit raw formats -- quantization noise at 12
bits is already less than noise from other sources.

~~~
aaronbrethorst
Widest aperture is tricky. Most lenses are soft until you stop down a couple
times. And with regard to highlights, that sounds like sort of a modern day
restatement of Ansel Adams' classic "expose for the shadows and develop for
the highlights." You never want to blow your highlights since you can't
recover detail from them.

~~~
judk
How is that possible? If you expose for shadows, you will blow out highlights
before you develop.

~~~
devindotcom
Not with Ansel Adams' setup! Shooting straight to JPEG will do that, though.

~~~
platz
yep, negatives have a "shoulder" at the top of the exposure curve which might
be poor quality, but there is still information there.

Coversely, extreme underexposure means there is basically no information on
the negative[

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aaronbrethorst
Interesting, but I wish they would've given more information on how they
metered the cityscape. "Underexposed" can be a very relative term, as some
parts of a non-uniform image will need more exposure than others to be
properly exposed, hence the reason why HDR is a thing.

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SixSigma
Interesting article. Not just for the photographic analysis but also how
quickly fancy things on the Web date.

"Mouseover to compare" and Mouseover menus all killed off by touchscreens. I'm
glad about drop down menus, they are a UI mistake, even on desktop
applications; Wirth and Raskin warned us about that.

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001sky
by Emil Martinec © 2008

last update: May 22, 2008

> worth noting (2008) in the title for reference

