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ETTR

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Offline pigeonhill

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ETTR
« on: 03 / July / 2019, 08:35:16 »
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I'm playing with the idea of an ETTR script and would be interested in hearing if anyone else had looked into such functionality...and got things working  ;)


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Offline waterwingz

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Re: ETTR
« Reply #1 on: 03 / July / 2019, 09:56:57 »
Quote from: pigeonhill on 03 / July / 2019, 08:35:16
I'm playing with the idea of an ETTR script and would be interested in hearing if anyone else had looked into such functionality...and got things working  ;)
Well, it has been five years since you posted "Holy Grail timelapse using auto ETTR". 

AFAIK, no additional progress although the script shooting hooks needed have certainly matured since then.  Perhaps reyalp's Raw Meter Intervalometer will do what you want?
« Last Edit: 03 / July / 2019, 10:01:37 by waterwingz »
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Offline pigeonhill

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Re: ETTR
« Reply #2 on: 03 / July / 2019, 12:12:15 »
@waterwingz

That’s what I thought, which I found strange; as, over on ML, the auto ETTR is a killer function.

What I seek is ETTR without taking an image and accessible in Lua ;-)
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Offline reyalp

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Re: ETTR
« Reply #3 on: 03 / July / 2019, 13:13:12 »
Quote from: pigeonhill on 03 / July / 2019, 12:12:15
What I seek is ETTR without taking an image and accessible in Lua ;-)
In CHDK, you have to shoot an image to have access to full dynamic range raw pixel values.

You could try to do something with get_live_histo (https://chdk.fandom.com/wiki/Lua/Lua_Reference#get_live_histo), but the relationship between viewport YUV pixels and raw values isn't specified AFAIK.
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Offline pigeonhill

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Re: ETTR
« Reply #4 on: 03 / July / 2019, 15:26:22 »
@waterwingz

Thanks for the hint. Had a look at the LV histogram route and I’m keen to explore, but the Lua script info doesn’t help me enough with how to code things.

It would be great to look at someone else’s scripting of this functionality.
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Offline waterwingz

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Re: ETTR
« Reply #5 on: 03 / July / 2019, 16:34:42 »
Quote from: pigeonhill on 03 / July / 2019, 15:26:22
Thanks for the hint. Had a look at the LV histogram route and I’m keen to explore, but the Lua script info doesn’t help me enough with how to code things. It would be great to look at someone else’s scripting of this functionality.
I've been looking for way to implement a "light meter" function as the final thing missing in my GUI 3.0 project.  That would go into the compiled C code but, if I understand your application correctly, needs something similar to what you are seeking  (i.e. the ability to assess the current exposure "quality" when using the current Tv, Av, Sv, Ev offset values).  Maybe I've been overlooking what was done for the get_live_histo( ) function in my forlorn hope that a get_current_brightness( ) proc call will show up one day?  Hmmm ....
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Offline pigeonhill

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Re: ETTR
« Reply #6 on: 03 / July / 2019, 17:01:53 »
@waterwingz

In a perfect world, CHDK would have an ETTR raw functionality like Magic Lantern.

I use the ML ETTR virtually all the time for still photography.

In ML one chooses how to trigger the ETTR exposure, eg via a half shutter press or a key press.

You can also specify various parameters to help set the ETTR exposure.

As I say, in a perfect world ;-)
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Offline reyalp

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Re: ETTR
« Reply #7 on: 04 / July / 2019, 01:19:47 »
Quote from: waterwingz on 03 / July / 2019, 16:34:42
Maybe I've been overlooking what was done for the get_live_histo( ) function in my forlorn hope that a get_current_brightness( ) proc call will show up one day?  Hmmm
I've thought about making something parallel to the rawop functions for live view, but the fact that I've never seen anyone use get_live_histo in a real script suggests interest is low.

FWIW, you can also abuse motion detection to get averaged values from regions of the screen, by running md_motion_detect with a short timeout and then using md_get_cell_val
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Offline c_joerg

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Re: ETTR
« Reply #8 on: 04 / July / 2019, 02:08:37 »
Quote from: pigeonhill on 03 / July / 2019, 17:01:53
I use the ML ETTR virtually all the time for still photography.

I am also very pleased with the function ...
ETTR makes sense in my view, but only with RAW data. The pictures are sometimes much underexposed. This can’t be corrected in JPG.

Quote from: reyalp on 04 / July / 2019, 01:19:47
I've thought about making something parallel to the rawop functions for live view, but the fact that I've never seen anyone use get_live_histo in a real script suggests interest is low.

Is get_live_histo RAW based?
The question is also how accurate is the histogram in darkness and long exposure times.

I have no idea how ETTR is realized in ML. If you have a RAW histogram of a picture and it is underexposed, you can calculate the exposure quite accurately for an ETTR image. However, if the RAW histogram is already clipped, then you cannot calculate how many steps you have to underexpose so that this no longer occurs.
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Offline pigeonhill

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Re: ETTR
« Reply #9 on: 04 / July / 2019, 10:03:52 »
Over on ML there are three raw-based LV features: a raw spotmeter; a raw based histogram that shows ETTR; and auto ETTR setting.

For example https://www.magiclantern.fm/forum/index.php?topic=5693.0

As I say, if CHDK could over some of this functionality it would greatly add to its raw based capability.  Note I say raw based based, ie not jpegs.

Then there would be the chance to extend the Lua api, to link to such raw based based functionality.
« Last Edit: 04 / July / 2019, 10:07:49 by pigeonhill »
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