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Old Sep 25, 2006, 01:20 PM   #1
jdl8422
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HDR Photo Question

I just recently discovered HDR photos. I have been reading up on them online. From what I understand you need to take several images at different ranges to get all the different values, then you basically merge them all to get a dynamic range of values. My question is, is there a way to do an HDR from one RAW photograph? The reason I ask is what if you want to take a picture of a person or a subject that is not stationary. Can you just take one RAW photo and adjust the levels and save it several times, then make one HDR?
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Old Sep 25, 2006, 01:44 PM   #2
ChrisA
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Quote:
Originally Posted by jdl8422
I just recently discovered HDR photos. I have been reading up on them online. From what I understand you need to take several images at different ranges to get all the different values, then you basically merge them all to get a dynamic range of values. My question is, is there a way to do an HDR from one RAW photograph? The reason I ask is what if you want to take a picture of a person or a subject that is not stationary. Can you just take one RAW photo and adjust the levels and save it several times, then make one HDR?
Yes and No. The RAW file contains maybe one and a half f-stops more range then a JPG can have. So of course you could adjust the contrast of the raw file so that it can "fit" into a monitor's or prints dynamic range. This is exactly like what people do in the darkroom when they select a paper grade to print on. Saving the image twice gains you nothing as you can't squeeze more information out of the RAW file than what the camera recorded in that one exosure wich is only a stop or two more then JPG. What I do is select _parts_ of the image and apply levels/curves adjustments to the shadow areas. I always expose for th highlights. Selective adjustment of the darker parts of the image is logically equivalent to what you proposed but much less work In Gimp you'd use a selection, in PS I think a "quick mask"

If you do the techique where you bracket the exposure you gain as many f-stops of dynamic range as you are willing to make exposures. The limit is "believability" at some point the image looks faked
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Old Sep 25, 2006, 01:44 PM   #3
Zeke
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You can't make an HDR from one raw image, but you can take one raw image with multiple exposures saved separately and combine them. Then using layer, mask out the parts you don't want of each exposure.
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Old Sep 25, 2006, 02:22 PM   #4
ATD
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A RAW file contains about 12 to 14 bit depth. A HDR can have upward to a 32 bit depth. Bit depth is not linear, so a 32 bit depth is a very deep range to play with, far greater than a single RAW file. Like the others said, even if you could make a HDR from a single RAW file you would not gain anything from it.


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Old Sep 25, 2006, 05:23 PM   #5
spicyapple
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Quote:
Originally Posted by jdl8422
My question is, is there a way to do an HDR from one RAW photograph? The reason I ask is what if you want to take a picture of a person or a subject that is not stationary. Can you just take one RAW photo and adjust the levels and save it several times, then make one HDR?
Yes. Photomatix can create HDR images from a single RAW file.

I tried saving multiple exposures from a single RAW file and combining it in PS, but PS gave me an error.
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Old Sep 25, 2006, 05:26 PM   #6
jdl8422
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the reason i asked the question was basically to see if you can make a HDR photograph of something that isnt stationary. Something like a person, I mean it will be difficult to take several exposures of a person. they would have to be perfectly still.
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Old Sep 25, 2006, 05:34 PM   #7
ATD
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Quote:
Originally Posted by spicyapple
Yes. Photomatix can create HDR images from a single RAW file.

I tried saving multiple exposures from a single RAW file and combining it in PS, but PS gave me an error.

Good to know that, thanks for the link.


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Old Sep 26, 2006, 10:35 AM   #8
tvguru
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Quote:
Originally Posted by spicyapple
Yes. Photomatix can create HDR images from a single RAW file.

I tried saving multiple exposures from a single RAW file and combining it in PS, but PS gave me an error.
From the FAQ from the site you linked:

Can't I just create the exposures from one RAW file?
Not really. Your RAW file contains data captured by the sensors for only one exposure. The total dynamic range you can reconstruct from one photo converted with different exposure settings can never be more than the dynamic range captured by your camera, and this is rather limited (see above).
When you are using only one exposure to capture the scene, your RAW file is already your HDR image.
Converting the RAW file to images with different exposure levels is a bit like slicing the dynamic range of the RAW into several parts. Combining back the parts into an HDR image will at best re-produce the dynamic range of the initial RAW file.
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