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Holy Grail timelapse using auto ETTR

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Offline pigeonhill

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Holy Grail timelapse using auto ETTR
« on: 07 / June / 2014, 12:16:03 »
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I have been away from this forum for some time, enjoying Magic Lantern on my 5DIII and IR converted 50D.

With the latest ML we have auto-ETTR and in camera timelapse.

Does anyone know if CHDK has got anything like this for Holy Grail timelapse capture, eg a function or a script?

I have an S95 and haven't upgraded my CHDK for a while.

Cheers
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Offline waterwingz

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Re: Holy Grail timelapse using auto ETTR
« Reply #1 on: 07 / June / 2014, 13:21:52 »
I don't believe that anything has happened since your last discussions with lapser : http://chdk.setepontos.com/index.php?topic=9270.80
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Offline pigeonhill

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Re: Holy Grail timelapse using auto ETTR
« Reply #2 on: 07 / June / 2014, 13:33:31 »
Waterwingz

Thanks for the quick response. I looked through the posts and had come to that conclusion, but I thought I would ask, just in case I had missed anything.

Pity, as I think an ETTR based approach to holy grail timelapse would be a real nugget for CHDK.

I guess I will have to see if my scripting is good enough :-o)
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Offline waterwingz

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Re: Holy Grail timelapse using auto ETTR
« Reply #3 on: 07 / June / 2014, 13:41:36 »
Quote from: pigeonhill on 07 / June / 2014, 13:33:31
Waterwingz

Thanks for the quick response. I looked through the posts and had come to that conclusion, but I thought I would ask, just in case I had missed anything.

Pity, as I think an ETTR based approach to holy grail timelapse would be a real nugget for CHDK.

I guess I will have to see if my scripting is good enough :-o)
I only half followed the thread with lapser at the time.  Did anything come of it? 

I'm not even sure I really understand the whole ETTR concept. Is it simply a question of itteratively increasing the exposure to get the histogram to shift right until a specified percentage of the pixels saturate ?  Does it matter whether you do this via Tv (integration time) or ISO (amplifer gain) adjustments?  To do this in CHDK,  you would need to take multiple shots,  although I suppose you might be able to block or delete the intermediate once (not sure this can currently be done cleanly though).

One change in CHDK that might help is that reyalp added "hooks" to the shooting process that can be exploited from a Lua script.  The forum thread that discusses this is here :  http://chdk.setepontos.com/index.php?topic=11081.0   I don't believe anyone has done a lot with it so far but it seems to cry out for a "cool"  or "holy grail" application.  Reyalp did include a sample script that might be tweaked to do what you want assuming you are okay with taking multiple images until the optimal exposure is reached.
« Last Edit: 07 / June / 2014, 13:48:41 by waterwingz »
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Offline pigeonhill

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Re: Holy Grail timelapse using auto ETTR
« Reply #4 on: 07 / June / 2014, 13:58:04 »
Waterwingz

The auto-ETTR approach relies on a (RAW) Histogram based assessment of the exposure to ensure no data is saturated in the highlights, or a specified amount is.

Thus A-ETTR is called each time before a timelapse image is taken, and exposure time and/or ISO adjusted.

The resultant images have many jumps, but software, eg LRTimelapse, deals with this in post.

Cheers
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Offline waterwingz

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Re: Holy Grail timelapse using auto ETTR
« Reply #5 on: 07 / June / 2014, 14:00:38 »
Quote from: pigeonhill on 07 / June / 2014, 13:58:04
Thus A-ETTR is called each time before a timelapse image is taken, and exposure time and/or ISO adjusted.
So you set the exposure for the next shot based on the results from the previous shot?  How aggressively you adjust each shot will determine if the next shot has too many blown pixels such that you need to back off for the following shot?
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Offline Microfunguy

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Re: Holy Grail timelapse using auto ETTR
« Reply #6 on: 07 / June / 2014, 15:48:08 »
Quote from: pigeonhill on 07 / June / 2014, 12:16:03
.
Does anyone know if CHDK has got anything like this for Holy Grail timelapse capture.

How is that relevant to solving the 'holy grail problem' ?
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Offline pigeonhill

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Re: Holy Grail timelapse using auto ETTR
« Reply #7 on: 07 / June / 2014, 16:14:55 »
What I mean is, is there an easy way, like with Magic Lantern, to invoke a RAW-based auto-ETTR check, between, timelapse capture frames.

In other words, the user does not have to handraulically intervene with shutter speed or ISO changes. The auto-ETTR functions ensures highlights are not blown out and the image gas the 'best' tonal capture.

This timelapse data set can then be 'thrown' at, say, LRTimelapse, which has an algorithm to pick out the holy grail key frames.

Cheers
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Offline waterwingz

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Re: Holy Grail timelapse using auto ETTR
« Reply #8 on: 07 / June / 2014, 17:48:45 »
Quote from: pigeonhill on 07 / June / 2014, 16:14:55
What I mean is, is there an easy way, like with Magic Lantern, to invoke a RAW-based auto-ETTR check, between, timelapse capture frames.
Did you try reyalp's sample script at the link I posted above?
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Offline pigeonhill

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Re: Holy Grail timelapse using auto ETTR
« Reply #9 on: 07 / June / 2014, 17:57:25 »
Waterwingz

Yes that looked interesting and I will look into it on my return: on international travel at the moment.

Over and out on this subject.........for now:-o)
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