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Old Nov 20, 2008, 6:22 PM   #1
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I did a search before posting and didn't come up with anything, though I feel sure this must have been discussed before.

Anyway, I'm trying to figure out how the feature works, so as to take most advantage of it. I've read how it is supposed to impart HDR benefits to the final composite image, but I just don't see it happening. People have described the final composite as an "average" of all the frames, but the results I get don't suggest this.

From what I can tell, the final image is merely a sum of all the previous exposures. If I take three shots with each exposed normally, then the final image is overblown consistent with a shutter speed three times as long as it needed. So the tactful approach to take - and this is what the camera apparently does if you enable auto EV adjust - is to divide the exposure time for normal exposure by the total number of intended frames and use this as exposure time for each frame. Of course, you wouldn't have to use exposure time explicitly, but whatever combination of exposure time, aperture, and iso to the same effect.

So anyway, in playing around with changing out exposure value between each frame or keeping them all the same my results consistently suggest that I'm getting nothing more than the sum off all the exposures. Nowhere in this process is HDR incorporated. In fact, if the multi-exposure were averaging the frames instead of adding, this still wouldn't give you HDR, it would just create an image you could achieve in one shot anyway if you had the exposure settings correct. To get HDR you have to have some kind of algorithm cherry picking the most desirable parts of each (differently exposed) frame to put into the final composite.

Lacking HDR, multi-exposure still has some interested possibilities, I'm just a little disappointed.

Can someone prove me wrong? I'd love to have some in-camera HDR...
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Old Nov 20, 2008, 9:12 PM   #2
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Hi Pwithem,
I could be totally wrong here because I've never fooled with HDR but, I was under the impression you could only achieve HDR with a computer program plus multi exposures of different settings. also has to be done with a tripod so each is in identical position.
I know there are those here that are good with this technique, somebody will jump in with the correct info soon I'm sure.:-)
good luck,

GW :bye:
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Old Nov 20, 2008, 9:20 PM   #3
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GW,
I am in agreement with you. I read the following before I set out to figure how multi-exposure works, and I think what Bart explains is incorrect, although his application toward moving water is clever and effective.

http://forums.dpreview.com/forums/re...712&page=1

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Old Nov 20, 2008, 9:49 PM   #4
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As I read his post, he says he is able to boost shadows a lot in p-p, so the hdr part is not done in the camera. Auto EV, I think, has to be enabled in the menu. (don't have that feature on my *ist D, but I can do multi exposures)

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Old Nov 20, 2008, 10:09 PM   #5
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there is a small button top left on the back of the K10D which will give you multiple exposures at different exposures
when i used it took 5 photos, you can change the exposure setting and the sequence you want the exposures to be in the menu

be aware
if you only take 3 photos for instance the next photo you take will follow the exposure sequence and not start again from the begining exposure

i shot many a photo at the wrong exposure because i forgot i pressed that button

i am at work at the moment so i cant check my camera or settings
but i am pretty sure thats how it worked


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Old Nov 20, 2008, 11:05 PM   #6
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There's two different topics being talked about here. I've played around a bit with the multi-exposure mode on the K20 (I never tried it on the K10). There's the option to let the camera compute exposure so that however many frames you chose for your multi-exposure, the final output (the picture that incorporates all of the pictures) is properly exposed. The picture I posted for last month's challenge was a multi-exposure done in camera.

That's different than the exposure bracketing that the camera can also do - where it takes 3 or 5 shots, changing the exposure between the shots so you have a range of exposure for HDR software to use, what John was talking about. That's different than shooting multi-exposure.

You can't use auto bracketing with multi-exposure on the K20 (p. 103 of the manual). I haven't actually tried to manually change the exposure when shooting different segments of a multi-exposure (you'd have to have a tripod as any movement of the camera at all would give you dizzying ghost images) so I don't know how that would work. I've been meaning to try it but just haven't gotten around to it yet. From your experience, it doesn't sound like it will work all that well.

I did try to use multi-exposure to smooth water when shooting a fountain. However, I found water like that a tricky thing - you still have to use shutter speeds slow enough to smooth the water some. Otherwise you get ghostly water drops throughout the frame, however many sets of them you have frames to your multi-exposure.

I played around a bit with CS4's HDR option, combining a couple of auto-bracketed pictures. Either there's something more to the settings than what I figured out, or else CS4's module isn't all that great - it still showed the one section of the picture blown out though one exposure had it correctly exposed, and took out a lot of the color in the mid-tone section because of the significantly underexposed frame. Perhaps if I only use 2 frames - the two extremes? I'm starting to think that Photo Matrix is the only way to go.
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Old Nov 21, 2008, 12:51 AM   #7
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mtngal wrote:
Quote:
There's two different topics being talked about here. I've played around a bit with the multi-exposure mode on the K20 (I never tried it on the K10). There's the option to let the camera compute exposure so that however many frames you chose for your multi-exposure, the final output (the picture that incorporates all of the pictures) is properly exposed.
Quote:
As I understand it, when you do this, it will average out a lot of noise in the dark areas, enabling better looking results when shadows are boosted, either with an HDR routine, or through using shadows/highlights.
Quote:
I haven't actually tried to manually change the exposure when shooting different segments of a multi-exposure (you'd have to have a tripod as any movement of the camera at all would give you dizzying ghost images) so I don't know how that would work.
Quote:
Would this work with the auto EV mode? If so, it could be a possible way to get something approaching HDR in camera.
Quote:

I played around a bit with CS4's HDR option, combining a couple of auto-bracketed pictures. Either there's something more to the settings than what I figured out, or else CS4's module isn't all that great - it still showed the one section of the picture blown out though one exposure had it correctly exposed, and took out a lot of the color in the mid-tone section because of the significantly underexposed frame. Perhaps if I only use 2 frames - the two extremes? I'm starting to think that Photo Matrix is the only way to go.
Quote:
Haven't used PS for this. With Photoimpact, it is pretty easy with a static scene. With motion in the picture, there is a way to mask out what you don't want, but it is pretty tedious, and I haven't gotten very good results. It does auto align the exposures, if there is minor movement between shots, so I have been able to do some hand-held HDR. The best feature, IMO, is that I could profile my camera, using 5 full-stop brackets, and save the profile. Now, I am able to use a single exposure, and turn it into HDR using the saved profile. Works very well, if I don't try to push it too far.
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Old Nov 21, 2008, 4:25 AM   #8
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as everyone has allready said, you cant do hdr "on camera" you need to use software, i use MediaChance Dynamic Photo HDR, you can download a trial version here http://www.mediachance.com/hdri/index.html

its very simple to use and you can get some very good effects, even using just 1 photo and when shot in jpg, not sure how it does that lol

i used it to transform this really greydull looking photo into something i was really pleased with.


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Old Nov 21, 2008, 8:18 AM   #9
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good input everyone. When I first started using the multi-exposure and taking double images of objects (myself, lamps, q tips, etc.), I saw how the clone objects looked ghostlike. My immediate impulse was, I want to make fully exposed clones and not ghosts. So, I figured out a way to do this in camera, but it requires some constraints on what you're shooting.

What makes it possible is that the multi-exposure is adding images instead of averaging them. By adding, I mean that a completely black pixel would have a value of 0 and anything brighter than that would have some value like 10 or 92, etc. So the key to having non ghost clones is that you fully expose the clone in each image, but you have to ensure that minimal or no light information is added to that same space in subsequent frames. The best way to do this is to use a black background.

The black background would need to be more perfectly black the more frames you want to add. Noise would also add, so low ISO is probably a good idea. I tried it out handheld with an image of two qtips on a black leather chair and it looked convincing.

Oh, and to do this, you have to disable auto EV adjust, because it does the math so that the final image is "properly" exposed, but since you only have clone in each frame, each clone needs to get a full exposure. Also, you want to avoid overlapping your clones or you'll get a bright ghostlike contribution - the same as if not using a black background.

Anyway, maybe this is all oldschool, but I didn't know I could do this until I figured out hwo the multi-exposure was working.
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Old Nov 21, 2008, 8:56 AM   #10
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Thanks for clarifying a couple of things - what you posted wasn't "old hat" to me at all. I've only just started to play around with multi-exposure and HDR options, so I'm a bit at a loss on how to do all this.
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