That's because the HDR process expands the total available dynamic range which in turn reduces contrast. You can simulate this effect by taking an image and compressing its range by using Levels to set the *output* to say, 50-200. If you then examine the histogram you'll see it has "shrunk" and moved to the middle.

That's what HDR does for each exposure moving this shrunk histogram to its appropriate place within the "total dynamic range" histogram space, so to speak. The result is an image which (in theory) contains the dynamic ranges of all of the composite images but each one only occupies a portion of the available range which, as shown above, has the appearance of reducing overall contrast.

Actually, the real problem is the display. If we had displays with the same dynamic range as an HDR image the image would look vibrant. Just look outside your window. That real world doesn't have this problem because we can perceive its full dynamic range.

To overcome this a number of methods have been devised when converting this "mega" dynamic range to what our displays can handle. Generically they are known as "local contrast enhancements" or "tone mapping". Like everything "auto" this sometimes works. Mostly not. The common artifacts are "hallos", false-color (looks like "out of gamut" tool), etc. So - for me anyway - it's best done manually.

Which then begs the question "why bother" with HDR? And the answer - for me at least - is *noise*! An HDR image clears up the noise so I can boost those dark impenetrable Kodachrome scans shadows without worrying about ugly noise artifacts.

BTW, I don't use PS, and I'd really like to try it out but a ~350 MB trial is a bit much for me to download right now.

Don.

On Tue, 10 May 2005 15:57:51 GMT, "Got Whiz? Cheese that is..." wrote:

Thanks the funny thing. They look fine before I bring them in to HDR. They only get... well for lack of a better term blah after they go through HDR.

"JJS" wrote in message

"Got Whiz? Cheese that is..."
wrote in message

Generally I have found HDR images come out dark and drab. Lots of detail sure, but still in need of some levels work and I would rather do that at the 32-bit level than 16-bit or 8-bit.

So adjust them before you bring them into HDR.

jazzman2005

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