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12-23-2008, 05:30 PM   #1
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K20D continues to amaze - buffered processing

There I was last night with a crystal clear sky. So I decided to check out a few things with the K20D by doing a star trail shot:

1) Plugged in the remote cord.
2) Plugged in the AC->DC converter and plugged it into an outside AC outlet.
3) Set it up on the tripod with the old M28/2.8, the widest lens I currently have.

Set it to ISO200 with EDR on, opened up the lens, set the shutter to B, locked the shutter open with the remote and went inside. I couldn't get Polaris in the shot due to the narrower field of view but I wasn't checking out much more than the cold weather and long exposure capabilities of the K20D. Besides, setting infinity focus is a bitch on this lens because the infinity focus stop inside has worn off so I always have to check focus visually. This isn't easy with little light at bone-chilling temperatures so I was expecting the focus to be off a bit.

Then I left the kit working while I went inside for a while. After a long wait, I stepped outside in the -24C (-11F) chill and closed the shutter on the remote. Knowing that I had a *long* time ahead for the in-camera noise reduction to take effect, I went back inside. Having forgot to actually time the exposure, I was going by feel for how long I needed to leave it. So when I actually brought the camera back inside (wrapped in a sweater) and pulled out the SD card, I was pissed to see that I hadn't waited long enough and there was nothing written to the card.

OK, I thought. Maybe this is a smarter camera than I know and if I put the card back in and turn it on, it will finish the processing. So I reinserted the card, plugged it into wall power and turned it on. I left it for at least half an hour and checked it again. And the image was there!!! I couldn't believe it. Turned out the exposure was 75 minutes long. Pentax had apparently assured that processing was buffered and saved if power was lost during processing. This is so good to know. I think I'll try it again just to see if I can replicate it.

Oh, yes, the focus of the image was as crappy as I had thought it would be. But the in-camera dark frame subtraction is very good with the K20D and there was no banding at all. How much having the camera chilled to the bone helped here, I don't know, but it could not have hurt. Further dark frame subtraction in post-processing got rid of what was left of the grain and hot pixels.

This camera continues to impress me.

Jack

12-23-2008, 09:47 PM   #2
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clever little bugger isn't it?
12-24-2008, 12:20 AM   #3
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No Surprise There

As you have mentioned, it is the Dark Frame Subtraction.

The camera has to hold two frames in its frame buffer. One for actual image and the other with shutter closed (but with the same amount of exposure time). It will not be surprised if the camera stores the two frames in its buffer until it finishes the processing. If any user operation can affect this lengthy process and even the image will not be written, I would regard this is a bug.

IMO, what you have seen should be considered as Normal but not a miracle.

Of course, you shouldn't pull the SD card when the camera was still "thinking"! :-)

My old old *ist D did the same. And yes, it did not fail in any way until it writes the final subtracted image.

Anyway, I don't like that the K20D has to force the user to get every long exposed picture dark frame subtracted owing to the possibly much obvious and numerous hot pixels during longer exposures. In fact, dark frame subtraction cannot do all the magics. It just turns hot/bright pixels into dark pixels afterall, which can be equally horrible depending on the scenes!

Cleverer algorithms will interpolate adjacent pixel values to fill the "dark pixels", but then this could be rather complicated for the algorithm itself and I bet normally most DSLRs won't do that in-cameraly (nor it is viable as much processing and intelligence would be required).
12-24-2008, 06:55 AM   #4
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My first question is why did you pull the SD card out? surely an easier way to check would be pressing the playback button? I guess it doesnt matter, but sounds to me like youre lucky you didnt go and pull the battery out!

Yes, this is pretty amazing stuff, but what would be REALLY amazing is if we could TURN THE DAMN DARK FRAME SUBTRACTION OFF!

12-24-2008, 07:58 AM   #5
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Aye it's some piece of kit for sure.
12-24-2008, 08:26 AM   #6
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QuoteOriginally posted by IsaacEastgate Quote
My first question is why did you pull the SD card out? surely an easier way to check would be pressing the playback button? I guess it doesnt matter, but sounds to me like youre lucky you didnt go and pull the battery out!

Yes, this is pretty amazing stuff, but what would be REALLY amazing is if we could TURN THE DAMN DARK FRAME SUBTRACTION OFF!
A momentary lapse of reason, I suppose. And yes, all K20D owners have voiced their opinion on not being able to turn off the DFS. I suppose we will see this being selectable in the next model churn.

Jack
01-16-2009, 03:39 PM   #7
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Not being able to turn off DFS is a major turn-off

QuoteOriginally posted by jbinpg Quote
There I was last night with a crystal clear sky. So I decided to check out a few things with the K20D by doing a star trail shot:

1) Plugged in the remote cord.
2) Plugged in the AC->DC converter and plugged it into an outside AC outlet.
3) Set it up on the tripod with the old M28/2.8, the widest lens I currently have.

Set it to ISO200 with EDR on, opened up the lens, set the shutter to B, locked the shutter open with the remote and went inside. I couldn't get Polaris in the shot due to the narrower field of view but I wasn't checking out much more than the cold weather and long exposure capabilities of the K20D. Besides, setting infinity focus is a bitch on this lens because the infinity focus stop inside has worn off so I always have to check focus visually. This isn't easy with little light at bone-chilling temperatures so I was expecting the focus to be off a bit.

Then I left the kit working while I went inside for a while. After a long wait, I stepped outside in the -24C (-11F) chill and closed the shutter on the remote. Knowing that I had a *long* time ahead for the in-camera noise reduction to take effect, I went back inside. Having forgot to actually time the exposure, I was going by feel for how long I needed to leave it. So when I actually brought the camera back inside (wrapped in a sweater) and pulled out the SD card, I was pissed to see that I hadn't waited long enough and there was nothing written to the card.

OK, I thought. Maybe this is a smarter camera than I know and if I put the card back in and turn it on, it will finish the processing. So I reinserted the card, plugged it into wall power and turned it on. I left it for at least half an hour and checked it again. And the image was there!!! I couldn't believe it. Turned out the exposure was 75 minutes long. Pentax had apparently assured that processing was buffered and saved if power was lost during processing. This is so good to know. I think I'll try it again just to see if I can replicate it.

Oh, yes, the focus of the image was as crappy as I had thought it would be. But the in-camera dark frame subtraction is very good with the K20D and there was no banding at all. How much having the camera chilled to the bone helped here, I don't know, but it could not have hurt. Further dark frame subtraction in post-processing got rid of what was left of the grain and hot pixels.

This camera continues to impress me.

Jack
OMG! The K20 doesn't deserve accolades for this!

The fact that we are FORCED to wait the same amount of time for a DFS is absolutely ridiculous!

I've been doing astrophotography for years now and anyone with knowledge of this type of digital photography understands that a DFS is usually necessary to remove noisy pixels, it is also understood that you usually only need one reference DFS image for any group of similar long exposures. You do not need a DFS for every photo. In addition, sometimes post processing will usually correct errors without the need of a DF reference.

Unless Pentax makes the DFS an option, this camera is virtually useless for exposures of 1 minute or more.

What photographer wants to waste his/her time waiting twice as long as the initial exposure before taking the next shot?

And for those that argue that CMOS is noisier and that Pentax had no choice, I suggest you check out most of all of the Canon CMOS based cameras, such as the 20D, 30D, 40D, and 50D. They don't insist on a DFS!

Has anyone else contact Pentax about this? I have and all I received was a caned message that this is how the camera was designed.
01-16-2009, 06:22 PM   #8
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The accolade was not for forcing DFS on the user. I have bitched about this ever since I got the camera. It was for buffering the process so the shot wasn't lost between power cycles.

Jack

01-17-2009, 01:48 AM   #9
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QuoteOriginally posted by jbinpg Quote
The accolade was not for forcing DFS on the user. I have bitched about this ever since I got the camera. It was for buffering the process so the shot wasn't lost between power cycles.

Jack
I understood but I am still really, really ticked off that despite so many of us complaining to Pentax, they have ignored addressing this issue for us.

I am beginning to suspect a flaw in the hardware which is algorithmically covered-up by the forced DFS! I am not normally into conspiracies but what else explains this issue being apparently unacknowledged for a year or more?
01-17-2009, 08:58 AM   #10
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QuoteOriginally posted by jbinpg Quote
How much having the camera chilled to the bone helped here, I don't know, but it could not have hurt.
I used to work with microscopes and laboratory grade cameras used for microphotography used some form of cooling for their CCD and CMOS sensors. The colder temperatures actually help image sensors by reducing the noise of an image.
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