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[OM] Re: HDR attempt

Subject: [OM] Re: HDR attempt
From: Dan Mitchell <danmitchell@xxxxxxxx>
Date: Tue, 29 Jan 2008 21:54:43 -0700
Moose wrote:
>> One thing that confuses me is that an "HDR" image actually has a lower 
>> dynamic range than the original scene did
> Not in the 32 bit mode used by some HDR apps. I'm too lazy to do the 
> research and math, but I think 32 bits may be enough to encompass the 
> range from direct sun, as seen on a clear day through the atmosphere, to 
> below the lowest threshold of light for the adapted eye.

  Well, 32 bits just gives you more resolution, but surely dynamic range 
is the difference between 0 and the top, not the number of steps in the 
middle. 1 bit would be enough if you're really not picky, 8 bits is 
certainly enough to represent a scale between total blackness and "the 
sun up close" -- there just wouldn't be a lot of detail available in the 
'interesting' range.

> So the combined capture can be true HDR - in a file. What you are 
> dealing with is the lack of display technology to actually display 
> anything like the full range of brightness. 

  Exactly -- if monitors were a:big enough to force the eye to 
open/close to compensate for varying brightness, and b:better at subtle 
shades of darkness and able to be much brighter, then this could be 
close -- and at that point, you'd want to have a lot of resolution to 
take advantage of that extra range of brightness.

> Even slide film could hold more DR than most photo paper can display. 

  And depending on how opaque unexposed slide film is, and how bright 
the bulb in the projector is, you could possibly get close to the real 
world.

> From fairly early on in 
> the development of film to now, one of the skills of a good photographer 
> has been to compress and/or clip that range of tones into a form that 
> reads as realistic to the human eye. That process is, for example, the 
> basic reason for being of the Zone System.

  My point exactly == "compress and/or clip" is reducing the dynamic 
range of a scene to a range that works for display on the medium in 
question, be that a monitor or photo paper.

  HDR images with tone compression and the like are just doing this with 
a larger original dynamic range than has been previously possible. (hm. 
I suppose with judicious masking and bracketed negatives, you could do 
the same thing in a darkroom, it would just be awkward).

  -- dan


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