Hi Seeker
In Photoshop CS3 there is a “Merge to HDR” function which works as follows:
When you have a scene that contains deep shadows and bright highlights, a single exposure cannot manage the full range of brightness levels, so either the shadow areas are black and show no detail, or the highlight areas are completely white and burned out.
Photoshop CS3 can compensate for this. For a terrestrial scene, using a tripod mounted camera, you expose 3 or 4 images at the same F stop, but varying the shutter speed for each image.
Image #1 has a slow shutter speed (e.g. 1/30 sec) so that detail is revealed in the shadows.
Image # 2 is exposed at say 1/60 sec for the mid tones.
Image # 3 is exposed at say 1/125 sec for some highlights.
Image # 4 is exposed at say 1/250 sec to show e.g. details in the sky and clouds.
The CS3 HDR function then automatically combines all 4 photos, using the correctly exposed shadows in Image #1 through to the correctly exposed highlights in Image #4.
Hope that makes sense!
Cheers
Dennis
PS - Have a look here
http://www.luminous-landscape.com/tutorials/hdr.shtml for a CS2 tutorial. It shows a 7 frame blend from almost black to almost burned out, and how they were combined to produce quite a pleasing final photo showing the full dynamic range.
Here is an astronomy example
http://www.astropix.com/HTML/J_DIGIT/PS_HDR.HTM