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Re: [OM] Bracketing for snow

Subject: Re: [OM] Bracketing for snow
From: Moose <olymoose@xxxxxxxxx>
Date: Tue, 03 Feb 2009 15:18:01 -0800
Chuck Norcutt wrote:
> I don't think your use of "tonal range" is correct here.  The tonal 
> range of the input is what it is.  

I knew that sentence was going to get me in trouble. And it did, even 
after rewriting. I mean to say that the 16 bit processing and output of 
RAW converters are capable of handling an even greater range of 
brightness than is present in any current RAW files that I know of. Of 
course it can't add dynamic range that's not in the original.

> Somewhat greater in a raw file than a JPEG with perhaps up to 1 stop or so of 
> additional highlight and shadow 
> detail.  But the tonal range of the 12 or 14 bits is not improved by 
> converting to 16 bits... it's only scaled upward.  For example, with 12 bit 
> input the maximum value for pure white is 4095.  In 16 bits it's 16535 or 16 
> times larger.  During the conversion of 12 bits to 16 bits all the 12 bit 
> values are simply multiplied by 16 and 4095 becomes 16520 (as close as you 
> can get to 16535 on an integer conversion).
>   

I've hoped it's something like that, rather than fully stretching fewer 
to more values.The advantage would be in the low values, where binary 
representation in the lowest bits leaves only coarse steps available for 
interpolation during editing.

16 bit histograms in PS don't show gaps in such converted files, but 
that may be by design. I dunno.

> The advantage of the 16 bits is that the additional range over the JPEG is 
> retained and, as you frequently point out, editing produces fewer integer 
> truncations and star-stepping when dividing numbers downward when reducing 
> pixel brightness during editing.
>   

Yup, the greater the tonal resolution, the smoother the results of 
interpolation.

Moose
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