Thanks, Moose. The original dng does not look terribly underexposed. I
can still see details in the shadows. Here it is:
http://www.pbase.com/tinamanley/image/160035214
Any more exposure and there would be even more totally blown out. I've
always resisted using higher ISOs but I guess I'll try and see if it makes
a difference.
Tina
On Mon, May 11, 2015 at 5:39 PM, Moose <olymoose@xxxxxxxxx> wrote:
> 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
>
> --
> What if the Hokey Pokey *IS* what it's all about?
>
> --
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