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Re: [OM] IMGS: Baracoa, + Banding?

Subject: Re: [OM] IMGS: Baracoa, + Banding?
From: Moose <olymoose@xxxxxxxxx>
Date: Mon, 11 May 2015 14:39:48 -0700
On 5/10/2015 6:26 PM, Tina Manley wrote:
...

This particular photo was very dark.  The ISO is only 320 but there is
severe banding in the shadows.  Why?  It's there in the original dng
without any manipulation.  If the ISO is 320, just like most of the other
B&W's in low light, why is there so much banding in this one?

http://www.pbase.com/tinamanley/image/160019998

Methinks you misunderstand the technology. There are certain combinations of camera bodies and lenses that band because of RF interference, or some such, but I don't think that's the problem here.

This shot is deeply underexposed. I'm guessing from some of my own shots that a good exposure for this scene is in the vicinity of 8 stops above what you took. That's about what an averaging meter would give. That would, of course, give a daylight like exposure, which is not what you want. However, given a static subject, tripod and highlights that will be blown either way, full exposure, then pulling the middle down in post, will generally give the best results.

You don't have that luxury with this subject. The only solution is higher ISO 
and perhaps slightly slower shutter speed.

This is an analog to digital device; it records analog input digitally, which has a problem in A to D conversion. In the highlights, all is wonderful. The top few stops have thousands of brightness values to record what the sensor 'sees'. In the middle, there are still enough values to exceed what our eyes can differentiate. At the bottom, there are fewer and fewer values available. At the very bottom, there are only two values, 0 and 1, black and white.

When you underexpose this much, you force the middle tones to be recorded in a part of the histogram where there are few values and force the shadows down into "insufficient information" land.

You seem to think the banding (of this sort) is, or should be, an artifact of high ISOs, when the opposite is the case. When you force the camera to record everything in the bottom of the histogram, then when you pull it up in post, there just isn't enough information to recreate the tonal detail that was squished (technical term) in recording. When you use higher ISOs, the camera amplifies the analog sensor signal before converting it to digital. The result is generalized noise, but not banding.

Bigger apertures and slower shutter speeds fix it all by delivering more light 
to the sensor, but aren't available here.

Another, broader way to look at it is that forcing anything, from material to system to person, beyond it's limits will result is failure of some sort. By underexposing, then trying to raise shadows well above any actually useful level, you forced this particular system beyond its limits into failure. It happens to be banding.

If you want to find the practical limits, set up a test with static subject, bracket exposures over a broad range and process them. You can find the minimum exposure that gives the results you want at your desired ISO.

Does anybody know how to get rid of banding?

1. Underexpose less.

2. Since it's in areas that should be deeeep shadow on any print or web display, don't worry about it, 'cause nobody can see it. Certainly no one, including me, saw any problem with the image as posted.

3. NR can sometimes help. Blurring works pretty well in areas like sky with no 
detail.

Techie Moose

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What if the Hokey Pokey *IS* what it's all about?
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