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multiple exposure

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Offline titaniq

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multiple exposure
« on: 08 / October / 2009, 08:11:54 »
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i wonder if it could be possible with a PS camera to take multiple shoots in one single frame, to realize something like http://photoshare.shaw.ca/image/2/d/8/63987/eclipse-0.jpg , without using a photo editor to blend several pictures.

I think of something like during a long exposure shoot of 15'' the iris to be closed let's say for 3 times, 3'' each.
Of course i can do this manually by placing a black paper in front of the camera  :D , but i wonder if this is possible with chdk.

what do you think?
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Offline barret

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Re: multiple exposure
« Reply #1 on: 08 / October / 2009, 08:30:47 »
i think this needs some hardware hacking and i don't think it's easy.
especially when you can acheive same results relatively easily. by making few shots and composing them together.
sometimes you have to balance gains and costs of such things and estimate, is it really worth it.
although the idea is nice :)
greets
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Offline barberofcivil

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Re: multiple exposure
« Reply #2 on: 08 / October / 2009, 08:37:30 »
Quote from: titaniq on 08 / October / 2009, 08:11:54
i wonder if it could be possible with a PS camera to take multiple shoots in one single frame, to realize something like http://photoshare.shaw.ca/image/2/d/8/63987/eclipse-0.jpg , without using a photo editor to blend several pictures.

I think of something like during a long exposure shoot of 15'' the iris to be closed let's say for 3 times, 3'' each.
Of course i can do this manually by placing a black paper in front of the camera  :D , but i wonder if this is possible with chdk.

what do you think?

You can set up a script to take individual shots and then combine them later.  CHDK also has RAW sum and RAW average feature in the file browser that lets you compbine raws on-camera.
Much like extra long exposures, you would likely get nicer results using this method than one single shot as I think there would tend to be less noise due to the combining process.
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Offline fudgey

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Re: multiple exposure
« Reply #3 on: 18 / October / 2009, 15:43:56 »
Forgive me if I'm wrong, but didn't Dataghost try that stuff in his old experimental branch thingie, I suppose by calling Canon fw functions CloseMShutter and OpenMShutter? If that's true (and if those functions can be found for all cameras at least yours), it would be trivial to add script commands to enable this for a single camera (but tedious to add support for all cameras because entry points need to be found & checked for all fw subs separately).

But you'll probably get better image quality by combining shots, because the sensor noise won't stop gathering to the photo just because you've closed the shutter (and before anyone says it, this script command wouldn't be enough to shoot dark frames at will, because the shutter will always open for a little while first).
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Offline reyalp

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Re: multiple exposure
« Reply #4 on: 18 / October / 2009, 17:59:47 »
There is really no reason to try to take multiple exposures in real time with a digital camera. Stacking the raws later can give you exactly equivalent results.
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Offline Xevailo

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Re: multiple exposure
« Reply #5 on: 09 / February / 2011, 18:09:27 »
I'm sorry for digging this up, but as titaniq I'd like to know whether a scrip like this existed or would be possible. And I think there are definitely reasons for real time multiple exposures:
- Not everyone owns picture-processing-programs such as Photoshop
- Those who own them may not know how to combine the pictures
- Others may simply refuse to manipulate their images on a pc
- Last but not least multiple-exposure images offer instant results and don't require any post-processing
Therefore I could really use a script like this for my Powershot G11, so if anyone knows where I could find one that'd be awesome.
Oh, and if there doesn't exist such a script but it would be possible to write one, I'd be willing to pay about up to 10$ for a working one (negotiable ;) ).
Greetings,

Xevailo
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Offline reyalp

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Re: multiple exposure
« Reply #6 on: 09 / February / 2011, 21:27:50 »
Quote from: Xevailo on 09 / February / 2011, 18:09:27
I'm sorry for digging this up, but as titaniq I'd like to know whether a scrip like this existed or would be possible. And I think there are definitely reasons for real time multiple exposures:
- Not everyone owns picture-processing-programs such as Photoshop
Plenty of free programs are capable of doing this.
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- Those who own them may not know how to combine the pictures
I'm not sure why you think these people would be able to figure out how to do it in CHDK. PC software is generally easier to use and better documented.
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- Others may simply refuse to manipulate their images on a pc
Users arbitrarily deciding to cripple their imaging capabilities is not something CHDK should try to solve.
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- Last but not least multiple-exposure images offer instant results and don't require any post-processing
Therefore I could really use a script like this for my Powershot G11, so if anyone knows where I could find one that'd be awesome.
"Stacking the raws later" does not necessarily mean off camera. You can use the "raw sum" or "raw average" to stack images on camera. Raw sum is the equivalent of a traditional multiple exposure. You can use raw develop to create a jpeg to view on camera.

Edit:
There is at least one valid reason to take multiple exposures on the camera: Taking them faster than you can save images. This can probably be done using lua and event procs, similar to the dark frame script: http://forum.chdk-treff.de/viewtopic.php?f=7&t=2157
« Last Edit: 09 / February / 2011, 21:42:24 by reyalp »
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Offline fudgey

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Re: multiple exposure
« Reply #7 on: 12 / February / 2011, 05:58:49 »
Quote from: reyalp on 09 / February / 2011, 21:27:50
There is at least one valid reason to take multiple exposures on the camera: Taking them faster than you can save images. This can probably be done using lua and event procs, similar to the dark frame script: http://forum.chdk-treff.de/viewtopic.php?f=7&t=2157
...and for those who don't read German that well, the original script is here http://chdk.setepontos.com/index.php?topic=5822.msg57106#msg57106.

And yes, I suppose one could modify that script to for example set Tv to 10 seconds and open the shutter for 50 ms twice per second (or at each USB remote key press). But exposure times shorter than 10 ms (1/100 s) may be difficult to achieve with acceptable accuracy unless we have access to a timer with better resolution that could be polled from Lua...? But then again the mechanical shutter may be too slow for fast exposures anyway.
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Offline fudgey

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Re: multiple exposure
« Reply #8 on: 12 / February / 2011, 11:16:27 »
Oh well, find a Lua script evolved from the dark frame script attached along with a tiny small image of a hand in front of a wrinkly and wet black t-shirt for proof  :D I tested this briefly on my a570, CHDK trunk 1054 (with native calls enabled).

The script shoots a long exposure with shutter opened shortly at instants specified by USB remote presses, for time specified by the user. The default is a 8 second shoot with 100 ms (1/10 s) exposures.

The script requires native calls to be enabled in your CHDK build. They are not enabled in CHDK autobuilds by default. Set OPT_LUA_CALL_NATIVE=1 in builconf.inc and rebuild to enable them. See script comments for more info (it's pretty much copied from the dark frame script so if that worked for you without modification, this should too).
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