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10-21-2008, 03:51 PM   #16
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QuoteOriginally posted by bentax Quote
Erm? Is that site on crack?
my thoughts exactly. My K20D doesn't do this, does it?

10-21-2008, 05:55 PM   #17
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QuoteOriginally posted by Mike.P Quote
Pentax adds HDR capabilities to their latest DSLRs

Quote : The user then simply needs to access the camera's HDR mode through the menu dial, set the camera up for the first shot, press the shutter, and off it goes. The internal sensors will then take three shots and combine them into a single HDR image.
This is not what in camera HDR does. In camera HDR on the K20D is just a "simulation" of HDR from 1 picture (and not a very good simulation). There is no camera yet that does HDR automatically, you need to post process from one picture processed once for shadows and once for highlights or bracketed exposure.
10-21-2008, 06:52 PM   #18
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QuoteOriginally posted by flyer Quote
This is not what in camera HDR does. In camera HDR on the K20D is just a "simulation" of HDR from 1 picture (and not a very good simulation). There is no camera yet that does HDR automatically, you need to post process from one picture processed once for shadows and once for highlights or bracketed exposure.
when you multiple exposure & bracketing available I would think that with just firmware change you have in camera hdr (3 or 5 shot), be a great selling feature IMO
10-22-2008, 03:08 AM   #19
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QuoteOriginally posted by deejjjaaaa Quote
Favourite Feature of the K10D - Multi-exposure (images) [Page 1]: Pentax SLR Talk Forum: Digital Photography Review

if you are talking about a feature that Pentax put in K10D/K20D to make it easier, but it is NOT classic HDR
I might be being stupid, but I don't see how this could possibly work. All the exposures are additive, so what is the difference between this and a single shot?

You are just building up the total exposure additively rather that all at once. Why should it make a difference?

Please let me know what is wrong with my thinking.

10-22-2008, 08:17 AM   #20
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The difference from the single shot comes by changing the exposure settings between shots. From what I've read (I haven't tried the multi exposure mode yet), the difference is this:

Lets say the scene you are taking a photo of has a DR of 10 stops. And lets say the camera sensor can record 8-stops of DR. And lets assume a single exposure that clips a stop at the bottom and one stop at the top.

If you are doing a two-shot exposure, and you don't change the camera settings (aperture, shutter, etc) for both captures, then pixels that are overexposed in the first image are overexposed in the second image, and when you put them together the are still overexposed. So in this case you don't have any difference compared to a single shot (other than motion being blurred and noise being reduced). Same goes for underexposure.

However, if you are taking two exposures with different exposures, lets say at -1EV and +1EV, things change. The first shot will capture all the shadow details, but overexposes the upper two-stops of DR. The second shot captures all the highlights, but clips the lower two stops of shadow detail. However, when you add them together, the composite image will contain both shadow data from the first shot and highlight data from the second shot, covering the full 10-stop DR of the scene. But, because the highlight detail and shadow detail aren't present in both shots, they can get compressed. In this case, the top and bottom 2 stops of image are compressed, and the middle 6 stops are equivalent as the single exposure.

Check out this post from the linked thread for an illustration:
I can illustrate what Richard described: Pentax SLR Talk Forum: Digital Photography Review
10-24-2008, 01:42 AM   #21
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QuoteOriginally posted by wcleong Quote
The difference from the single shot comes by changing the exposure settings between shots. From what I've read (I haven't tried the multi exposure mode yet), the difference is this:

Lets say the scene you are taking a photo of has a DR of 10 stops. And lets say the camera sensor can record 8-stops of DR. And lets assume a single exposure that clips a stop at the bottom and one stop at the top.

If you are doing a two-shot exposure, and you don't change the camera settings (aperture, shutter, etc) for both captures, then pixels that are overexposed in the first image are overexposed in the second image, and when you put them together the are still overexposed. So in this case you don't have any difference compared to a single shot (other than motion being blurred and noise being reduced). Same goes for underexposure.

However, if you are taking two exposures with different exposures, lets say at -1EV and +1EV, things change. The first shot will capture all the shadow details, but overexposes the upper two-stops of DR. The second shot captures all the highlights, but clips the lower two stops of shadow detail. However, when you add them together, the composite image will contain both shadow data from the first shot and highlight data from the second shot, covering the full 10-stop DR of the scene. But, because the highlight detail and shadow detail aren't present in both shots, they can get compressed. In this case, the top and bottom 2 stops of image are compressed, and the middle 6 stops are equivalent as the single exposure.

Check out this post from the linked thread for an illustration:
I can illustrate what Richard described: Pentax SLR Talk Forum: Digital Photography Review

Thanks for the explanation and link.

Again I have tried to get my head round this but I remain sceptical. The only way that I can see this working is if the camera is much more intelligent than I take it to be. Once the highlights are blown, (i.e. the sensor is saturated with photons) they cannot become "unblown" by adding even more photons.

Sorry If I am still being stupid.
10-26-2008, 12:16 AM   #22
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I think you might be getting hung up on the film equivalent. For example, when doing a multi-exposure shot with a film, once you blow a highlight it doesn't matter what else you do, that section of film is blown out. So if you were to take two exposures (lets say 0.7 secs for the shadows and 1/45 for the highlights and keeping the aperture constant), it wouldn't matter, your highlights would get destroyed when exposing for the shadows. If there is no motion, this is basically an addition, the equivalent of exposing the film (or a single picture) for a length of 0.7 + 1/45 = 0.722 seconds. So for film, no matter how you pick the exposures, you will not get any increase in dynamic range captured. And Film multi-exposure is an addition of each frame.

But there is a difference between a film camera and the K20D. The K20D has two multi-exposure modes, one that emulates the film version, and a new one that is only possible with digital (AFAIK). The mode is selected by the "auto-EV Adjust" checkbox. If this is not checked, then it is like a film camera, and you get no increase in DR. However, if you do select it, the camera doesn't add the exposures together, it AVERAGES them. So even though one image has the highlights blown out, the second has the highlights well exposed, and the net effect when you average the two is that you maintain highlight detail, but the DR of the highlights are half of what they are in the well-exposed image. Same goes for the shadows. The key is the average, and it's not an addition. So the resultant image will be like this: the portions of the image that are well exposed in both frames maintain the same DR as either frame, and the portions that get over-exposed/underexposed in only one frame will have half the DR compared to the well exposed frame for that highlight or shadow.

You've maintained your detail, you've just compressed the true DR of your scene into the 8-stop range that a JPG allows.

I also took some test shots to demonstrate this. I lit a portion of the frame (my bathroom) so that it metered at 1/45, and lit another portion so it metered 0.7". This range is larger than the DR of the camera (at least for JPGs). So for a single exposure at 1/8, both highs and lows get clipped:

Name:  pentax-1_8.jpg
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Now, for the multi-exposure I used two exposures, 0.7" and 1/45:

Name:  pentax-7.jpg
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Size:  21.7 KBName:  pentax-1_45.jpg
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The camera combined them with this result:

Name:  pentaxMulti.jpg
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Compare this the the 1/8 image from above. I think you could say that now the dark sections appear up reasonably well exposed compared to the 1/8, and the bright areas (the shower curtain especially) also has more detail that the 1/8 single exposure.

And to round things out, here are the histograms for the images:

Name:  histograms.jpg
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I apologize, the middle plot on the left is mislabeled, it should say 1/8 (instead of 1/20). I didn't feel like re-generating that plot. You can see that there isn't a single exposure frame that can cover the DR of the scene, and that the 1/8 exposure clips both highs and lows. But the multi-exposure image has a nice looking histogram, with very little clipping. The color of the wall behind the shower curtain does look like it's changed, perhaps I should have manually set the white balance, maybe thats what makes it look funny.

Anyways, hopefully that helps.
10-26-2008, 04:08 AM   #23
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The K20D built-in "HDR" feature has nothing to do with this. The above three images are examples of excessive application of a program like Photomatix to an exposure-bracketed series of shots (as has been said before).

Note that most photographers hanging out here at pentaxforums consider this kind of images bad photography, typically made by newbies, and that the Pentax Photo Gallery would never accept them. Personally, I feel one should experiment with the technology until one masters to get away w/o the artificial touch. I.e., an image which obviously is an HDR image normally is a bad image...

10-27-2008, 04:34 AM   #24
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QuoteOriginally posted by wcleong Quote

Anyways, hopefully that helps.

Again many thanks for your detailed exposition.

As they say, the proof of the pudding is in the eating so I will give it a go sometime and get back to you with my results.

Best wishes
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