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07-19-2009, 12:27 AM   #61
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QuoteOriginally posted by jstevewhite Quote
.....
I'm curious, though, how a software package can do DFS, since it can't create a dark frame exposure post-hoc.
Assuming the sensor noise is random, not particular to any pixel or group of pixels, and follows some sort of mathematical distribution (normal, skewed to one side, whatever), has some sort of known relationship with exposure time (doesn't even have to be linear) , its possible to simulate the noise mathematically and create an equivalent DFS.

There are a wide range of electronic design situations where engineers have to simulate the effect of noise, either produced by the circuit itself or forced from outside, even before a single piece of hardware has been build. Software-tunable "noise generators" are now an essential Computer-Aided design tool.
The idea of using random noise to cancel out other random noise is not new, but only recently have processors been fast enough to put it into practice.
I think they have just adapted bits of such technology into Post-Processing programs.

To avoid complex number crunching, digital cameras take an actual shot with the shutter closed. Very old-fashioned if you think how powerful digital processors have become these days. Mathematically generated DFS is definitely possible, depends on cost and complexity for the in-camera hardware, really.

07-19-2009, 12:44 AM   #62
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QuoteOriginally posted by jstevewhite Quote
Oh, good grief that would be awesome. But, if they did that, they'd have to release the byte code/machine code/compiler toolchain/something for their processor setup. But Pentax would *own* the *nix Geek Contingent, eh!?
As much as I would truly love to have my hands on the firmware source, it will never-ever happen. In fact, it would be just as likely that Apple would release the source for the IPOD.
07-19-2009, 12:53 AM   #63
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QuoteOriginally posted by kittykat46 Quote
Assuming the sensor noise is random, not particular to any pixel or group of pixels, and follows some sort of mathematical distribution (normal, skewed to one side, whatever), has some sort of known relationship with exposure time (doesn't even have to be linear) , its possible to simulate the noise mathematically and create an equivalent DFS.

There are a wide range of electronic design situations where engineers have to simulate the effect of noise, either produced by the circuit itself or forced from outside, even before a single piece of hardware has been build. Software-tunable "noise generators" are now an essential Computer-Aided design tool.
The idea of using random noise to cancel out other random noise is not new, but only recently have processors been fast enough to put it into practice.
I think they have just adapted bits of such technology into Post-Processing programs.

To avoid complex number crunching, digital cameras take an actual shot with the shutter closed. Very old-fashioned if you think how powerful digital processors have become these days. Mathematically generated DFS is definitely possible, depends on cost and complexity for the in-camera hardware, really.
Not quite, the noise is not actually random. In long exposures, a certain number of pixels will begin to go hot after a certain amount of time. That is the entire point of the second equally long exposure. The same pixels will go hot again, then the camera subtracts those hot pixels the first exposure.

As mentioned numerous times, the DFS doesn't need to take place immediately after a long exposure. Most/all photographers prefer to do the DFS after they are done taking photos. Unfortunately, if you own a K20D or K7, this is not an option.
07-19-2009, 01:52 AM   #64
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I couldn't be happier with the k7 and it's long exposure capabilities.

This was one of the first long exposures I took when I got the camera. Shutter was open for around 2 minutes.

Wheel of Brisbane on Flickr - Photo Sharing!

07-19-2009, 02:05 AM   #65
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QuoteOriginally posted by petercrane Quote
I couldn't be happier with the k7 and it's long exposure capabilities.

This was one of the first long exposures I took when I got the camera. Shutter was open for around 2 minutes.

Wheel of Brisbane on Flickr - Photo Sharing!
Lovely shot!
07-19-2009, 02:10 AM   #66
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QuoteOriginally posted by petercrane Quote
I couldn't be happier with the k7 and it's long exposure capabilities.

This was one of the first long exposures I took when I got the camera. Shutter was open for around 2 minutes.

Wheel of Brisbane on Flickr - Photo Sharing!
I haven't done anything more than 2 minutes yet (that's long exposure for me ), but I can second that.

The K-7 @ ISO100 does a very good quality, low noise capture at 2 minutes, no doubt about it.

I think its only the forced DFS which is controversial.
07-19-2009, 03:37 AM   #67
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Iím with pentaxmz here, I immediately switched off the DFS function on my K10. I just couldnít stand waiting for the camera spending half my photographing time doing DFS.
But I guess the result without DFS is so bad that if reviewers saw it the camera would be shot to pieces.
07-19-2009, 03:50 AM   #68
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I wasn't aware of this long exposure NR issue. TBH, over here when it's dark outside, it's usually so damned cold one prefers to stay inside anyhow. I recently bought a K200D to accompany my K20D. Do I gather correctly that this CCD sensor based model doesn't have the issue?

EDIT: OK, that seems to be the case. I just did some long bulb exposures with the lens cap on and if NR was on, it took about the same time as the exposure to display an image. But if NR was off, the image was displayed almost instantly.

Sorry about the semi off topic.


Last edited by emr; 07-19-2009 at 04:17 AM.
07-19-2009, 07:30 AM   #69
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QuoteOriginally posted by petercrane Quote
I couldn't be happier with the k7 and it's long exposure capabilities.

This was one of the first long exposures I took when I got the camera. Shutter was open for around 2 minutes.

Wheel of Brisbane on Flickr - Photo Sharing!
That's a great shot - but if aliens had landed and hung around for the next two minutes after the shutter closed, you'd have had to photograph them with your phone, 'cause your fancy camera was a worthless brick for that period of time - just sayin'...
07-20-2009, 01:26 AM   #70
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Just wondering: Do we have the same problem when shooting in RAW?
07-20-2009, 03:45 AM   #71
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QuoteOriginally posted by heliphoto Quote
That's a great shot - but if aliens had landed and hung around for the next two minutes after the shutter closed, you'd have had to photograph them with your phone, 'cause your fancy camera was a worthless brick for that period of time - just sayin'...
I think I'd be too afraid to photograph aliens in case they melt, suddenly attack me, or decide to steal my Pentax.
07-21-2009, 09:52 PM   #72
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QuoteOriginally posted by petercrane Quote
I couldn't be happier with the k7 and it's long exposure capabilities.

This was one of the first long exposures I took when I got the camera. Shutter was open for around 2 minutes.

Wheel of Brisbane on Flickr - Photo Sharing!
Nice photo... but Quality isn't the point. Like heliphoto, you've got your self a brick for as long as the initial photo took to capture.

I dare you to team up with a fellow Canon or Nikon photographer some night for a photo marathon (as you are already aware, there is a whole other world to photograph at night).... you might feel a little inadequate next to them. Comparing relatively similar cameras with similar IQs.... you and your Pentax are going get far fewer photos by the end of the evening when compared to the non-Pentax photographers.

As heliphoto said, I'm just say'n!
07-21-2009, 09:53 PM   #73
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QuoteOriginally posted by phvg Quote
Just wondering: Do we have the same problem when shooting in RAW?
Doesn't matter. If it did, I definitely wouldn't have a reason to complain.
07-21-2009, 09:55 PM   #74
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Has anyone written Pentax about the DFS matter?

I have and it's been about three weeks and with no reply! Nice!
07-22-2009, 07:51 AM   #75
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QuoteOriginally posted by phvg Quote
Just wondering: Do we have the same problem when shooting in RAW?
Yes. The forced DFS is applied even to RAW images.

The properties of a dark frame are typically consistent given a specific exposure time and rough sensor temperature. So to cover a fireworks show, a photographer could take shots of the show and then take a set of dark frames with representative exposure times at the end.

But with the K20D and K-7's forced DFS, this is not an option. I don't know how many great bursts I've missed due to the K20's forced DFS, which is one of the main reasons I never sold the K10D - I switch back to the old body for fireworks shows because the 20 is nearly useless for them.
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