Archived posting to the Leica Users Group, 2006/09/19

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Subject: [Leica] Re: the dynamic range of digital
From: telyt at (Douglas Herr)
Date: Tue Sep 19 18:22:09 2006
References: <> <p06230902c1362bb46c66@[]>

On Sep 19, 2006, at 4:49 PM, Henning Wulff wrote:

> At 4:18 PM -0400 9/19/06, wrote:
>> B. D. Colen <> wrote:
>>>  And of course, if one routinely underexposes by a stop, one is not 
>>> only
>>>  avoiding overexposure, one is also discarding about 20 percent of 
>>> all the
>>>  information captured by the sensor. ;-)
>> ???  can you explain  ???
>> I typically set the DMR to underexpose 1/2 to 1 stop (RAW files) and I
>> rarely if ever see clipping at either end of the histogram.
>> Doug Herr
>> Birdman of Sacramento
> This being digital, it generally works like this:
> Depending on how the chip/firmware are set up, the first (brightest) 
> stop or stop and a half have half the total bits of information in the 
> file, the next darker stop to stop and a half have a quarter of the 
> bits, etc. The darkest segment, where things start blending into 
> noise, holds only a fraction of a percent of the info.
> wugh away half of your bits. Fortunately, if you start out with a 12 
> or 13 useable bit depth, that's not that much problem because even 
> with fairly drastic maneuvering in Photoshop you won't get noticeable 
> banding in the dar areas, and besides, they're _dark_ areas, where a 
> bit of banding doesn't show up as much.
> No point in talking about some cameras having a 16 or even 14 bit 
> depth depth; true, useable bit depths really don't extend beyond 12; 
> possibly 13. Not even DMR's :-).

Do you have empirical or experimental evidence of this?

> The moral is: for highest quality try to expose so your histogram is 
> as far to the right (bright end) as possible, and yet clip only 
> specular highlights. Make sure you're looking at an RGB histogram, 
> because in the common luminance histogram one colour could be clipping 
> without you knowing it, causing serious, non-recoverable colour shifts 
> in highlights.
> In practice, I generally set exposure compensation to -1/3, and keep 
> an eye on the RGB histogram.

In my experience with the DMR, setting exposure comp to -.5 or -1 
sacrifices very little deep shadow detail if any.  It's not what I'd 
call a 20% loss of data.  The histogram (yes it's RGB) is nowhere near 
clipping at either end aside from specular highlights.  Perhaps B.D.'s 
20% estimate is based on his experience with the E-1?

Doug Herr
Birdman of Sacramento

Replies: Reply from bd at (B. D. Colen) ([Leica] Re: the dynamic range of digital)
Reply from imagist3 at (Lottermoser George) ([Leica] Re: the dynamic range of digital)
In reply to: Message from telyt at ( ([Leica] Re: the dynamic range of digital)
Message from henningw at (Henning Wulff) ([Leica] Re: the dynamic range of digital)