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Mult-Exposure Bracketing Based on Zebra

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Offline cantain

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Re: Mult-Exposure Bracketing Based on Zebra
« Reply #10 on: 26 / January / 2011, 19:43:47 »
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Thanks Lebeau

I'll give it a try.

Since I posted this inquiry I've been shooting 7 or 9 bracketed shots using the CHDK feature for this and my results are good. Maybe precision in terms of upper and lower limits of scene DR doesn't matter as long as your bracketing exceeds them.

cantain
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Offline geoffire

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Re: Mult-Exposure Bracketing Based on Zebra
« Reply #11 on: 07 / August / 2011, 02:55:38 »
In histogram.C I see where over_exposed and under_exposed globals are set - used for the indicators on the histogram - why not adjust the threshold as necessary and use those?
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Offline toinech

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Re: Mult-Exposure Bracketing Based on Zebra
« Reply #12 on: 10 / October / 2011, 18:54:54 »
May be a more convenient way would be to manually control the capture of different exposures:
1. Select a highlight/distance area to be captured
2. Select a shadow/distance area to be captured
3. Recompose and shoot.

The detailed process may be as follow:
1. Point the camera to the highlight area (or object at some distance), half shoot
    CHDK will record the exposure parameters (Av, Tv, etc...)
    User can subsequently validate this with an additional push of a custom button

2. Point the camera to the shadow area (or object at some other distance) , half shoot
    CHDK will record the exposure parameters (Av, Tv, subject distance etc...)
    User can subsequently validate this with an additional push of a custom button

2(.5): CHDK compute the bracket parameters based on bracketing mode (Av, Tv, subject distance, etc...)

3. Recompose the framing of the picture in order to take the shot and take the shot.
    CHDK will do the required bracketing based on the  parameters computed in (2.5)

This should be possible as the OSD Miscellaneous values show the exposure values?

Business case (:-) =
Focus bracketing
- Selective Near and Far field in macro or in
- Fore ground subject and infinite landscape under some low light conditions

TV bracketing
- Selective light and dark areas

...

Toine
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Offline toinech

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Re: Mult-Exposure Bracketing Based on Zebra
« Reply #13 on: 29 / October / 2011, 16:12:26 »
Quote from: hwntw on 05 / January / 2011, 09:08:11
Quote from: reyalp on 31 / October / 2010, 00:22:23
One of the ideas I've had along these lines is to automatically capture a RAW/DNG if the histogram shows lots of dynamic range in the scene.

You could do this in script with shot_histogram I think, but it means you have to use script for shooting all the time.
Quote
ps - almost forgot - it would also be nice to "lock" an exposure/focus point ( half-pressed shutter ) without holding the shutter button down - and then adjust the zebra pattern via EV, Tv, Av, etc. That would be too good! Maybe someone already achieved something like this.
Canons firmware already has AE and AF lock on many models, check your manual.
The problem with this suggestion is that exposure lock on my Ixus 95 is the same button which is used for changing Ev- half shutter/top button. Trying to change exposure turns AE lock off. I think that the original idea for an improved zebra remains a good one. If anyone wants to code something I am happy to test it.

I guess the whole point of doing EA lock is not to change exposure.
May be you want to Zebra to be displayed not only when half press so that you can do all the adjustment based on it?
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Offline hwntw

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Re: Mult-Exposure Bracketing Based on Zebra
« Reply #14 on: 30 / October / 2011, 17:41:37 »
yes, display zebra just like the histogram can be displayed- on all the time so that Ev adjustments can be seen working, as they are made
I think that "lock" did not really mean lock, but meant continuous display (of zebra)
Colin
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Offline toinech

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Re: Mult-Exposure Bracketing Based on Zebra
« Reply #15 on: 04 / November / 2011, 23:50:09 »
Quote from: hwntw on 30 / October / 2011, 17:41:37
yes, display zebra just like the histogram can be displayed- on all the time so that Ev adjustments can be seen working, as they are made
I think that "lock" did not really mean lock, but meant continuous display (of zebra)
Colin

I had quick look at the code for that section. Somehow, the code only displays zebra when half shoot. Easy modification to fix. However, it is not my piece of code I do not feel entitled to mess with it unless for my own personal use.
Toine.

PS: I'll let you know how it works with my A610. What's your camera?

Other though - so far we have over exposed zebra. We'll also need under exposed zebra so that you can adjust until some portion of the picture become too dark. This will give you the bracket range.
« Last Edit: 04 / November / 2011, 23:59:58 by toinech »
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Offline cantain

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Re: Mult-Exposure Bracketing Based on Zebra
« Reply #16 on: 16 / January / 2012, 02:49:58 »
Quote from: toinech on 04 / November / 2011, 23:50:09
Quote from: hwntw on 30 / October / 2011, 17:41:37
yes, display zebra just like the histogram can be displayed- on all the time so that Ev adjustments can be seen working, as they are made
I think that "lock" did not really mean lock, but meant continuous display (of zebra)
Colin

I had quick look at the code for that section. Somehow, the code only displays zebra when half shoot. Easy modification to fix. However, it is not my piece of code I do not feel entitled to mess with it unless for my own personal use.
Toine.

PS: I'll let you know how it works with my A610. What's your camera?

Other though - so far we have over exposed zebra. We'll also need under exposed zebra so that you can adjust until some portion of the picture become too dark. This will give you the bracket range.
Quote from: toinech on 04 / November / 2011, 23:50:09
Quote from: hwntw on 30 / October / 2011, 17:41:37
yes, display zebra just like the histogram can be displayed- on all the time so that Ev adjustments can be seen working, as they are made
I think that "lock" did not really mean lock, but meant continuous display (of zebra)
Colin

I had quick look at the code for that section. Somehow, the code only displays zebra when half shoot. Easy modification to fix. However, it is not my piece of code I do not feel entitled to mess with it unless for my own personal use.
Toine.


PS: I'll let you know how it works with my A610. What's your camera?

Other though - so far we have over exposed zebra. We'll also need under exposed zebra so that you can adjust until some portion of the picture become too dark. This will give you the bracket range.

Interesting! Can you post or PM the code for the mod to code? I'm using an S3iS.

About your idea from a previous post (3 steps for calculating DR range for bracketing) have you combined that procedure with the zebra display in your new code?

Since my original post way back in October 2010 I've been experimenting with many similar manual procedures. However the three step automated procedure you outlined would be almost ideal.

C.
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Offline toinech

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Re: Mult-Exposure Bracketing Based on Zebra
« Reply #17 on: 25 / January / 2012, 22:37:43 »
Need to change the following code from gui.c from:
2312   
2313       if (conf.zebra_draw)
2314           if (module_zebra_load())
2315                   if (libzebra->gui_osd_draw_zebra(conf.zebra_draw && gui_get_mode()==GUI_MODE_NONE &&
2316                                                           kbd_is_key_pressed(KEY_SHOOT_HALF) && mode_photo &&
2317                                                           !state_kbd_script_run)) {// no zebra when script running, to save mem
2318                           return; // if zebra drawn, we're done
2319           }

to

2312   
2313       if (conf.zebra_draw)
2314           if (module_zebra_load())
2315                   if (libzebra->gui_osd_draw_zebra(conf.zebra_draw && gui_get_mode()==GUI_MODE_NONE &&
2316                                                           mode_photo &&
2317                                                           !state_kbd_script_run)) {// no zebra when script running, to save mem
2318                           return; // if zebra drawn, we're done
2319           }

Works on my cam.

The 3 step process is still being worked on. I have not figured out the calculation part for the Tv bracketing as shoot half might change your Av and Tv at the same time for the second measurement. We want to keep the Av constant to avoid messing up with depth of field.
If Av(1) is the first Av to be kept then we will need to find out the Tv(n) for Av(1) value that gives same exposure value as the Tv(2) and Av(2) values collected in the second measurement. Unless you are already in Av mode.

Hope this helps,

Toine
« Last Edit: 25 / January / 2012, 22:51:50 by toinech »
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Offline toinech

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Re: Mult-Exposure Bracketing Based on Zebra
« Reply #18 on: 12 / April / 2012, 20:19:24 »
I made the change for the display of Zebra on my A540. This completely mess up with the rest of the OSD display. Unfortunately, I do not have a very good understanding of how Zebra work to fix it. :-(
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