[Leica] Re: the dynamic range of digital

[henningw at archiphoto.com (Henning Wulff)]

At 4:18 PM -0400 9/19/06, telyt@earthlink.net wrote:
>B. D. Colen <bd@bdcolenphoto.com> 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
>http://www.wildlightphoto.com

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 :-).

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.

BTW, the M8 can show RGB histograms.

-- 
    *            Henning J. Wulff
   /|\      Wulff Photography & Design
  /###\   mailto:henningw@archiphoto.com
  |[ ]|     http://www.archiphoto.com