HDR


RAB

Link Posted 07/10/2011 - 17:26
Here's one for ya!

I've used the HDR function in my K-x a few times now and got to wondering. Obviously, the camera takes 3 separate exposures, one at the correct exposure, one under-exposed and one over-exposed. It then combines these images using the in-camera software. All well and good, however ...

These exposures have a short time-lapse between them and when the subject has some elements with movement, eg a river, trees blowing in the wind, people etc, the time difference between the exposures shows up in the resulting HDR image.

Why not adapt the software to take one exposure, then produce the under and over exposed images electronically before combining them to produce an HDR image? This would deal with the time-lapse between exposures and result in fewer shutter actuations.

Am I missing something really obvious here? If not, I claim the idea as my own and demand a new 645 from Pentax in recompense.
"He's not the Messiah, ..."

wvbarnes

Link Posted 07/10/2011 - 18:23
Hi,

the version on the newer KR has the selectable option 'auto align' to help resolve any movement. The camera takes 3 frames in half a second by the way.

pentaxian450

Link Posted 07/10/2011 - 18:32
Auto-align won't solve the problem of movement caused by wind (or any other type of movement happening while the pictures are taken). It will align the frames when the three shots are taken hand held and there is a slight variation in the framing.
Yves (another one of those crazy Canucks)
Last Edited by pentaxian450 on 07/10/2011 - 18:32

Dave-L

Link Posted 07/10/2011 - 20:51
RAB wrote:
Why not adapt the software to take one exposure, then produce the under and over exposed images electronically before combining them to produce an HDR image? This would deal with the time-lapse between exposures and result in fewer shutter actuations.

Am I missing something really obvious here? If not, I claim the idea as my own and demand a new 645 from Pentax in recompense.

New pentaxian for here (though with 35 year old Pentax kit!), please don't jump on me if I'm wrong!

If the exposure is 100% perfect at the black and white ends, the extra two images then generated would be over exposed or under exposed respectively and would not help.

If the original shot was over or under exposed, the two extra images would not recover any lost detail any better than you could in post processing.

So any extra images generated from the first exposure would not extend dynamic range (I think).
K3/K5/10-17fisheye/15mmDA Ltd/18-55WR/55-300DA/100DFAMacroWR/50F1.4M/200F4M/DA*200F2.8/DA*300F4/DA*50-135/DA*60-250/Mitsuki 400F5.6/others.
Last Edited by Dave-L on 07/10/2011 - 20:54

simonkit

Link Posted 07/10/2011 - 21:44
RAB wrote:


Why not adapt the software to take one exposure, then produce the under and over exposed images electronically before combining them to produce an HDR image? This would deal with the time-lapse between exposures and result in fewer shutter actuations.

Am I missing something really obvious here? If not, I claim the idea as my own and demand a new 645 from Pentax in recompense.

I don't think there's much reason to do this in camera as it's easily achieved by shooting raw - infact that's exactly how I created the Conwy Castle image I've just posted but with 5 exposures 1/2 stop apart

Simon
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RAB

Link Posted 07/10/2011 - 22:48
simonkit wrote:
[quote:3496ace15f="RAB"]

I don't think there's much reason to do this in camera as it's easily achieved by shooting raw - infact that's exactly how I created the Conwy Castle image I've just posted but with 5 exposures 1/2 stop apart

I know this can be done with a bit of post-processing, but Pentax offer the quicker simpler route of producing HDR images in-camera. I quite like the ease of use and have had some good results, but I feel there could be a technically more advantageous method of achiving the same result.
"He's not the Messiah, ..."

davidstorm

Link Posted 07/10/2011 - 23:25
It's easier and often produces better results to take a single image and adjust the exposure on the raw file, saving differently exposed versions of the same shot and then processing these in software such as Photomatix. This guarantees perfect alignment and gives more control over the final picture. Depending on the subject and lighting conditions this can produce superb results.

Regards
David
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mdc

Link Posted 08/10/2011 - 04:30
I think the original question has been lost throughout the course of this thread... the reason why it doesn't do it in one exposure is simply a matter of physics; DSLRs still work essentially the same way as cameras always have; exposure is determined by a combination of aperture and shutter speed, since you can't expose with 3 different apertures/shutter speeds simultaneously (as DSLRs still use physical shutters), the camera has to take the shots one after the other.

However, it would theoretically be possible to open the shutter for the longest exposure, and then take sequential readings (like split lap timing) from the sensor during the course of the exposure. Not sure how this would work with CCD/CMOS technology though, although that's probably how things will go in the future.

The best way I've found to deal with this issue is either to go for really fast, or really slow shutter speeds. If you're using a decent camera with a good framerate, firing off your 3 (or even 5) shots at 1/250 to 1/2000 will take less than a second. The other option is to do long exposures, say 4 to 30 seconds, and then that way objects in quick motion will be completely absent from the final composite shot.

EDIT: Single-shot HDR is usually pretty appalling... the whole point about HDR is to re-introduce detail which was clipped out at either end during capture.
Last Edited by mdc on 08/10/2011 - 04:37

PierroJ

Link Posted 09/10/2011 - 18:17
mdc wrote:
.

EDIT: Single-shot HDR is usually pretty appalling... the whole point about HDR is to re-introduce detail which was clipped out at either end during capture.

I was just wondering about that myself. If one were to take just a single shot of a scene where a bracketed shot was needed ( bright sky / dark foreground for instance ), which end of the spectrum would you shoot for ?

If you expose for the bright sky, you'll be trying to bring up detail from a dark foreground, which i find is never the best option. So, if exposing for the dark foreground instead, you'd bring down the over exposed sky, which should be the better option for addressing 3 exposures in RAW from a single shot.

Still, i think the one shot option is riskier.
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simonkit

Link Posted 09/10/2011 - 18:30
PierroJ wrote:
mdc wrote:
.

EDIT: Single-shot HDR is usually pretty appalling... the whole point about HDR is to re-introduce detail which was clipped out at either end during capture.

I was just wondering about that myself. If one were to take just a single shot of a scene where a bracketed shot was needed ( bright sky / dark foreground for instance ), which end of the spectrum would you shoot for ?

If you expose for the bright sky, you'll be trying to bring up detail from a dark foreground, which i find is never the best option. So, if exposing for the dark foreground instead, you'd bring down the over exposed sky, which should be the better option for addressing 3 exposures in RAW from a single shot.

Still, i think the one shot option is riskier.

Personally I always make sure I don't clip the highlights as that's where most of the image detail is, also having moved from the K20D to the K5 it's impressive just how much more detail can now be recovered from the shadows without inducing any significant noise - the K5 is really in a different league than previous Pentax models in this respect.


.
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PierroJ

Link Posted 09/10/2011 - 18:34
Yup, i hear that a lot about the K-5, and after my next post office blag, i'll be in the market for one
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