Measuring exposure performance (was Re: proposal - script shooting hooks)

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This is an isoinc run from SX230. Meter96 looks more noisy as from S110 an G1x. Well, this cam has a smaller Sensor…

I would like to compare my cameras under identical conditions . But it's hard because the exposure time is constantly changing . It would certainly be helpful if you had a parameter for the exposure time .
Or any other idea?

Can I do something like set_tv96_direct(0) for 1s in the code?

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Offline reyalp

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I would like to compare my cameras under identical conditions . But it's hard because the exposure time is constantly changing . It would certainly be helpful if you had a parameter for the exposure time .
Or any other idea?

Can I do something like set_tv96_direct(0) for 1s in the code?
That's a good idea. For now, you should be able to set the exposure you want by replacing
Code: [Select]
local tv96 = get_prop(props.TV) + d_sv96 - start_ev_shift*96
with your own tv96 value. For one second, use 0.
Don't forget what the H stands for.

This is a nearly identical isoinc run with G1x, S110 and SX230 with 1s exposure time in range ISO100 to ISO400. For me it looks like there is not really a difference between the cams. In the second plot I tried to normalize the curves.



Re: proposal - script shooting hooks
« Reply #45 on: 08 / September / 2015, 04:45:05 »
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I don't think there should be oscillation in rawopint in constant lighting 

I would also expect so on constant lighting.

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if over or under protection isn't active, unless shutter speed is high enough to run into precision issues. However, I haven't actually tested like that, so maybe there is.

The second 100 pictures from rawopint_compare3, the part without modification show oscillation on constant lighting. Under protection was off, over not active and shutter speed around 1/4s. I see this in a couple of runs

The question is who constant the lighting was. I did it in a room without windows. The same environment as I used for all isoinc runs. The room has one filament lamp (200W / 50Hz) with non-electronically stuff inside. I’m not sure if a monitor would be better measure equipment.

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Another note, in theory we can set the shutter speed directly in microseconds. The actual precision of the hardware is unknown (a shutter testing script like isoinc would be useful), but it should be possible to adjust exposure in steps smaller than 1/96th ev for some of the range. This isn't currently possible through script though.

Interesting stuff.
I've always asked myself, how the implementation of tv96 to exposure time works.
On ISO I expect amplifiers as we discuss before.
On exposure time I would expect a digital timer. But when the lowest resolution is microseconds than the timer must be larger than 16Bit. So when you can modify the timer, you can play with the lowest Bit. Do you know where the highest shutter speed is?

Update:
To run some constant measures with isoinc, I could set  iso_start= iso_end=412 and  shots_per_step=100 or?
To get more accurate values, it would be helpful to set meter_step=1?





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Offline reyalp

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Re: Re: proposal - script shooting hooks
« Reply #46 on: 08 / September / 2015, 16:31:30 »
I've always asked myself, how the implementation of tv96 to exposure time works.
It follows the follows the APEX definition  (how precisely isn't certain)

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On exposure time I would expect a digital timer. But when the lowest resolution is microseconds than the timer must be larger than 16Bit. So when you can modify the timer, you can play with the lowest Bit. Do you know where the highest shutter speed is?
The exposure time is a 32 bit microsecond value, but I assume the flicker seen at high shutter speeds is related to physical limits. In the testing I've done, 1/16000 is noticeably darker than 1/8000, but I haven't got around to testing how close they are to the requested values or how consistent the results are. This should be relatively easy to now that we have raw meter.

At the other end, you can use a full 2000 seconds on some cameras, but quality suffers ;)

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Update:
To run some constant measures with isoinc, I could set  iso_start= iso_end=412 and  shots_per_step=100 or?
I think so, though I don't promise the script correctly handles start=end
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To get more accurate values, it would be helpful to set meter_step=1?
The default samples 57600 pixels, I wouldn't expect adding more to make much difference.

edit:
In my earlier comment, I said meter would tell you if the scene changes, but of course this isn't copletely correct, meter will change in the next frame if the requested exposure changes. Bv should should give you the absolute scene brightness, assuming there is no over or under exposure, and that the camera actually uses the requested exposure values.

In your compare3, the bv values show some slight variation.
« Last Edit: 08 / September / 2015, 16:40:20 by reyalp »
Don't forget what the H stands for.

Re: Re: proposal - script shooting hooks
« Reply #47 on: 09 / September / 2015, 02:18:46 »
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if the scene changes, but of course this isn't copletely correct, meter will change in the next frame if the requested exposure changes.
Of course, I understand it like this, meter has to change when exposure changes


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In your compare3, the bv values show some slight variation.
So I will do some investigation with different lighting situation including using a monitor…


Re: Re: proposal - script shooting hooks
« Reply #48 on: 10 / September / 2015, 14:52:07 »
I made 6 runs (each 100 shoots) under constant lighting condition with G1x.  I thought it would be constant...

1) Filament lamp, indirect light, F4, 1/2s
2) Halogen lamp, indirect light, F4, 1/10s
3) LED lamp, indirect light, F4, 1/8s
4) LED lamp, indirect light, F4, 1/8s
5) Monitor, 60Hz, F4, 1/25s
6) Monitor, 60Hz, F16, 0.6s

Run 1) are the same condition as I made with all isoinc runs.  There are changes from around 3/96 steps.  Really worse is the halogen lamp.  It looks like that the LED is better but she loses brightness over the time. It look like the monitor is the best solution for measure (when using longer shutter times). But also the monitor needs time, to get on the right temperature. 

Notice: The senor temperature increases from 30 to 45 degree on the end, but it looks like that this has no influence.

The log file shows on sv96=412 ==> sv=101. I thought, sv96=412 is exact ISO100…

Re: Re: proposal - script shooting hooks
« Reply #49 on: 10 / September / 2015, 17:13:50 »
Hi,
I follow your discussion and tests very interrested.
  I thought it would be constant...

1) Filament lamp, indirect light, F4, 1/2s
2) Halogen lamp, indirect light, F4, 1/10s

For 50Hz AC the the light of your lamps have a frequency of 100Hz.
Every 10ms you will have a peak in brightness.
Noone knows really how quick the naked exposure-measurement of the camera is. (not exposure time)

So  your exposure can differ depending to the position of the trigger.

A good idea to test this might be a 12V Halogen lamp with a good stabilized DC Power source.
IXUS 970 IS 100b

 

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