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Fredrik Eriksson wrote:
> On Thu, 06 May 2010 00:56:35 +0200, Jim Henderson <nos### [at] nospam com>
> wrote:
>>
>> I've actually wondered this myself - raw editing software gives you the
>> option to adjust the exposure; obviously, you can't pull details out
>> doing this that are completely washed out or completely underexposed, but
>> it is possible to bring additional detail out by making changes to the
>> exposure setting (ev) after the photo has been taken.
>>
>> I've done it, so clearly it's possible, I just don't understand the math
>> behind it.
>
> When the camera creates a JPEG file, part of the raw data is discarded and
> the rest is then adjusted to fit in the 0-255 range. The camera picks a
> black-point somewhere near the low end of the (raw) range, and all values
> below that are made black (i.e. 0) in the JPEG. Similarly, a white-point
> is selected, and all values above that are made white (i.e. 255). When you
> edit a RAW file, you have access to the parts that would otherwise have
> been cut off. If the exposure was somewhat less than perfect, there can be
> useful data in those parts.
In other words, the RAW format gets you High Dynamic Range.
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