Talk to Adobe about HDR. They will tell you and the plug-in in
Photoshop CS2 will not allow you to use three seperate images (with
different exposures done in ACR) for an HDR image. The plug-in
knows you are trying to use one image for the three and will not
allow you to do it.
Just because the software doesn't allow you to do something
doesn't mean there is no value in combining different 'developments'
of the same RAW file. Not allowing this is merely some software developer's
decision as to what they will allow their software to do. Do you
always follow the guidelines set down by authority figures?
Sounds so conformist.
Adobe has covered this very well. It doesn't work and can't be
done. Now if other software is allowing you to do this. It means
either the software is less picky and isn't doing the job right
and/or the software isn't very good and can't tell that you are
using the same image.
Who said it doesn't work? I do it all the time, with results that
I can plainly see, and which improve my images when they have
exposure issues. I am doing the job with Photoshop and ACR,
but not the HDR plugin. There are tutorials I could point you to
on the web explaining the technique of combining multiple
conversions of a given RAW file.
Part of the point here is that some cameras (DSLR's for sure,
I can't vouch for P&S's since I don't have one with RAW
output capability) have a wider gamut (larger color space)
than sRGB. The human eye can see more than sRGB jpeg
can encode in terms of color. One place this is quite apparent
is in the tendency of jpegs to have blown reds, a subject much
discussed here a while ago. Using a larger color space such
as Adobe or Prophoto RGB allows one to capture a wider gamut,
and using two different developments allows one to compress
the highlights and shadows of that color into the smaller
sRGB color space. I recently had a bright orange flower
with a hummingbird feeding on it.
In sRGB the flower was completely overexposed
if I used sRGB and kept the bird from being totally dark.
Using Prophoto RGB gamut allowed me to keep tonal range in
the flower without underexposing the bird. Alternatively, I could
use two RAW conversions, one for the flower and one for the bird.
The same holds true for overall luminance values. I often use
two RAW conversions of the same file and combine them
in layers, using them to lighten the shadows and/or bring back
the highlight details.
Personally, I will go with Adobe. It doesn't matter what you do to
a raw file as far as adjusting the exposure. The computer, the
software and the HDR plug-in sees all data in the file even if the
human can't. When you adjust exposure in an image you are adjusting
for the benefit of the humans looking at it and not the software or
the hardware. Just for the humans.
Take a dark shadow area. The computer and software know what is in
there. When you adjust it so you can see it, that is only for the
benefit of the human, not the software the software and the HDR
plug-in has always saw that data. Plain and simple.
You seem to have an overly restrictive conception of what the RAW
data represents. It is as the name indicates the unprocessed data
captured by the sensor. Any conversion of that data to another format
inevitably involves processing of the data. Vanilla conversion to
sRGB is not guaranteed to match ideally the sensor data, in fact
generically it clips in both the shadows and highlights
of some colors. One can use two conversions of the same RAW file
to bring the image data within the more restrictive confines
of the 8-bit sRGB gamut of a jpeg image.
I don't see why this amounts to fakery; it is
merely compressing the data to fit within the confines of an
overly restrictive standard of what digital color and exposure
should be, since indeed the human eye has a wider gamut than
sRGB, and one would like to represent the tonal range in
some way that our eyes can interpret and appreciate.
Granted, this may be less of an issue with P&S cameras
with their more limited dynamic range. But with DSLR's
it is definitely a useful tool, even if the people who developed
the HDR plugin couldn't think of a way to incorporate it
in their software.
--
emil
--
http://theory.uchicago.edu/~ejm/pix/20d/ 
