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05-22-2009, 09:25 AM   #1
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K7 HDR Bracketing - Why only 3 images ?

I've been having a quick peek through some of the preliminary specs for the forthcoming Pentax K7 and note that if they are to be believed, it's new High Dynamic Range feature appears to works solely in conjunction with Jpegs (not RAW images?) and is limited to a maximum of three bracketed images.

HDR (High Dynamic Range) Mode (One Composite Image from 3 Exposure Bracketed Images)
I was always under the impression that to be truly effective, at least 5 (possibly more ?) bracketed images were required to produce an effective finalised HDR image. My question is therefore:
Why only 3 bracketed images ? Your comments and constructive explanation on the subject would be most welcome ……..

Best regards

Last edited by Confused; 05-22-2009 at 09:37 AM.
05-22-2009, 09:38 AM   #2
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Maybe a limitation on what hte processor can handle, something to upgrade to on the next model. Could be to limit the file sizes form novice users getting carried away. Also could be that with the dynamic range capabilities of the new 77segment metering system all you need is 3 images.
05-22-2009, 10:15 AM   #3
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I think of this new functionality as "neato factor". It's first generation, mostly gimick that turns a few heads and hopefully generates some additional revenue. Once JP lifts the restriction on sample images and/or it hits the streets I could easily be proved wrong - but it seems like it would take a ton of horsepower and programming in-camera to produce "real" HDR imagery.

Based on what I've seen/heard it appears what they are offering is a one-touch solution for combining multi-exposure and one-touch bracketing (something a few of us thought would have been nice to have in the K20D) and applied some basic tonemapping.

That they are doing tone mapping precludes the output being "RAW" - it has been processed in-camera the same as if you had applied one of the other digital filter/effects. You can tweak the image properties all you want in the K20 (pretty sure K10 is the same but can't remember) but if you're shooting raw they do nothing unless the raw processing software you use in post decifers the info.
05-22-2009, 10:17 AM   #4
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Though the output is JPEG who is to say that the 3 images aren't actually full RAW captures? with -3, 0 and +3 EV captures you should be able to pull a LOT of information in terms of shadows and highlights from three RAW files. My guess that this will only work in JPEG mode because the output is JPEG. Can you image the size of a 3 image HDR PEF file from a 14.6mpx sensor? Or the amount of in-camera time it would take to make that PEF?

05-22-2009, 10:34 AM   #5
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Three images at distinct 1 ev steps are enough to create an HDR image. The amount of range is not really relevant compared to the response curve of the sensor (which Pentax knows very well). Most HDR software require at least 3 exposures to be able to reconstruct the response curve to know where to "line up" the three histograms and combine them (because "1 ev" apart is never exactly that amount). Again, this is something that in-camera firmware knows very, very well.

Also, it is easier to keep the images lined up to avoid the appearance of "ghosts" or slight misregistration "blur" if you have fewer images. The HDR feature in the K-7does not align the images like off-camera software, and no matter how stable your tripod and head, there will always be some shake when the mirror goes up and down. From what I've seen and read, the range of the images is probably 2 ev apart and computed from the raw files (as it takes 10-12 seconds to compute!). Finally, converting to JPEG first would actually take *more* time as the frames are held in buffer as raw after each shot anyways.

I got a good idea from this article by Jack Howard: But I'll know more after I try out the K-7 tomorrow.

Last edited by panoguy; 05-22-2009 at 11:33 AM. Reason: added URL and clarified
05-22-2009, 10:43 AM   #6
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Hi everyone

Thanks for your cogent replies on the subject.

Best regards
05-22-2009, 12:40 PM   #7
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There's a possibility that it's not doing tone mapping at all. I know there was a comparison to that, but I also know there's a third-party company offering firmware integration of an exposure blending system, similar to enfuse and other software. The source material for that is likely to be JPEGs due to the processing system used at present.
05-22-2009, 12:57 PM   #8

QuoteOriginally posted by Confused Quote
Why only 3 bracketed images ?
So they can offer 5 bracketed images in the next upgrade so you'll have to buy that.

05-22-2009, 04:51 PM   #9
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My guess is, adding two more will require almost twice the required on board memory, and almost twice the processing time. It takes 10-12 seconds to process 3 images already, I suppose anything longer will make this feature a hard sell.
05-22-2009, 05:05 PM   #10
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QuoteOriginally posted by song_hm Quote
My guess is, adding two more will require almost twice the required on board memory, and almost twice the processing time. It takes 10-12 seconds to process 3 images already
I guess it is because 6EV range is more than enough if you cannot interactively tweak tone mapping parameters for a decent result.

As far as "on board memory" is concerned: the K-7 has 2GB on board! So, this shouldn't be an issue ... at all
05-22-2009, 05:40 PM   #11
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Because the 3 frames are so you can create HDR on the run... the camera itself supports bracketing of 5 shots. So if you want to do the tone mapping yourself don't use the in camera HDR use the 5 shot bracket and then do it on a computer.

05-22-2009, 07:13 PM   #12
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Even with 3 shots, as long as it gathers all information required, it can be broken up and tone-mapped separately in PP.

5 shots just makes it easier to tone map each of them.

HDR is only required if the scene contrast is higher than the RAW capacity. In case of an overcast day, for example, HDR effects can be obtained easily with only 1 RAW exposure. 3 shots usually suffice (they can be 0, -3, +3 EV apart for what's worth), more shots are only required if there's information that falls outside the covered range...

For example, a part of your +0 EV shot may blow the highlights, but at -3 EV it becomes black. Therefore 1 exposure is needed between 0 and -3. Usually with modern sensors, this situation rarely happens unless the contrast of the composition is very, very high and you want every pixel of every channel not clipped in any way.

Last edited by wolfier; 05-22-2009 at 07:21 PM.
08-06-2009, 04:46 PM   #13
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QuoteOriginally posted by falconeye Quote
As far as "on board memory" is concerned: the K-7 has 2GB on board! So, this shouldn't be an issue ... at all
How do you know it? How come the buffer is relatively small compared to this amount of memory?
08-07-2009, 10:56 AM   #14
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HDR can be done with just two images 3EV apart, so in many cases you don't necesarilly need 3, let alone 5.
08-07-2009, 10:05 PM   #15
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QuoteOriginally posted by Miserere Quote
HDR can be done with just two images 3EV apart, so in many cases you don't necesarilly need 3, let alone 5.
True, in fact the free FDR Tools HDR program only allows two images, but still provides some decent results. Click here.

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