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

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Offline c_joerg

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #60 on: 29 / February / 2016, 15:08:06 »
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@reyalp:
Made just a fast run with isoinc on the S110 with 1s exposure time and ISO from 960 to 1040 (just 12 pictures)

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You mean to set the initial Tv? You should be able to use M mode. It should always stay the same between shots, unless you selected "Keep exposure constant"
Yes. I set manual 1s in M Mode, const_exp=true and start_ev_shift=0. But I did not get the 1s. So I fixed it in the code as you descript before.


I made 2 runs. One in continue and one in quick mode. As you can see, I can reproduce it and the result is different from the two runs. I can’t believe it why I have it not seen before….

From my last post here I had 2 open question. May be you find some time and give me a short answer. It will may be help me to understand a little bit more about the stuff..
« Last Edit: 03 / March / 2016, 13:17:11 by c_joerg »
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Offline reyalp

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #61 on: 29 / February / 2016, 16:34:35 »
Quote from: c_joerg on 29 / February / 2016, 15:08:06
Yes. I set manual 1s in M Mode, const_exp=false and start_ev_shift=0. But I did not get the 1s. So I fixed it in the code as you descript before.
That's what I get for going from memory rather than looking at the code. This is expected behavior, if the cameras current ISO doesn't match the lowest test value.

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From my last post here I had 2 open question. May be you find some time and give me a short answer. It will may be help me to understand a little bit more about the stuff..
Sorry, sometimes even a short answer takes lot of time :(

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The first thing which I notice was that I got sometimes from the pre shot ISO200. Yes, we have seen it before and it looks like this is some stupid stuff from G1x. So I fixed that in the code from isoinc.
I would guess this is just the camera being in auto-ISO at the start. Remember, this happens if CHDK ISO overrides have been used, even if the camera already had a specific ISO set. To get back to true manual ISO, you need to set something in the menu.

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Why the RAW values are not going under 512? Yes I know a little bit about the black level but not really much.
Some previous discussion https://chdk.setepontos.com/index.php?topic=7069.0

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The G1x has a 14bit AD Converter. The pictures with +3EV are totally overexposed. Why I can’t see 16384 in the RAW Data? Yes I know, it is an average of R G B Pixels.
I'm not sure what raw data you are looking at. isoinc meter value?
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Is this the answer that only on color goes to full scale?
Typically, the greens clip a lot before the red on a neutral subject.

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Is it possible just to meter one color?
Yes. the drtest.lua script does this, for example. In fact, I have a drtest csv file you sent me from G1x at some point. You can see the greens are clipping at +2 stops (I assume 16382 vs 16385 is probably due to some dead or weak pixels)
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Offline reyalp

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #62 on: 29 / February / 2016, 22:00:00 »
Quote from: MarkB on 29 / February / 2016, 19:30:27
I am happy to run the test, are there any specifications or parameters you need?  Or is just pointing the camera outside fine?

The subject should have constant, uniform lighting and not contain anything that moves. An LCD monitor showing a blank page or a blank wall under artificial light should be good.

Set the "ISO input type" to ISO, and enter the range of ISOs you want to test. For your test, you could just do something like 980 to 1020.

If you are only testing a small range like, you can set "Initial ev shift" to 0.

The other settings can be left default.

It's possible the "Shoot mode" setting will affect ISO override behavior.

Setting it  to "cont" and making sure continuous mode is enabled in the canon firmware should be most similar to your rawopint run that showed the funny ISO jump. If "quick" doesn't show the same behavior, you may be able to avoid the problem by turning off cont mode in rawopint.

edit:
FWIW, ISO overrides behaving oddly at high values is pretty common.  As mentioned in the first post, the last stop on some cameras is done entirely in JPEG processing, with no change in the raw data.
« Last Edit: 29 / February / 2016, 22:53:59 by reyalp »
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Offline c_joerg

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #63 on: 01 / March / 2016, 03:04:53 »
 
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This is expected behavior, if the cameras current ISO doesn't match the lowest test value.

Understood. This is the d_sv96 part. It might be easier, to set this value to 0, when the camera is in M Mode.

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Sorry, sometimes even a short answer takes lot of time

It’s OK. I know this. Maybe the time comes, where I can really support you.
Thanks about giving me the answers.

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I would guess this is just the camera being in auto-ISO at the start.

I’m really sure that the Camera was set to ISO100. On auto-ISO I could understand it…

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I'm not sure what raw data you are looking at. isoinc meter value?

Yes the meter values. But I understand now.

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If "quick" doesn't show the same behavior, you may be able to avoid the problem by turning off cont mode in rawopint.

But when I understand my measure correct, "quick" made it worse…

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As mentioned in the first post, the last stop on some cameras is done entirely in JPEG processing, with no change in the raw data.

Yes I understand this.
But everything which can be seen in the meter (or meter96) is not just a JPEG processing or?
In case, where is no change in the raw data, and the raw data is not overexposed, this can be corrected when you saving the RAW files and doing the JPEG processing on a PC or?
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Offline reyalp

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #64 on: 01 / March / 2016, 16:23:33 »
Quote from: c_joerg on 01 / March / 2016, 03:04:53
I’m really sure that the Camera was set to ISO100. On auto-ISO I could understand it…
Just to be clear: using any CHDK ISO override (script or menu) puts the camera in auto-ISO, even if the Canon UI looks like it is set to some specific ISO. So if you ran insoinc twice, without rebooting or manually changing the Canon UI ISO setting between runs, the second run would effectively start in auto ISO.

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But everything which can be seen in the meter (or meter96) is not just a JPEG processing or?
Right, what I mean by "in jpeg" is that we don't see it in the raw data. But this isn't the the issue we see on s110 or g1x, it's just a general point that "ISO" in the Canon firmware is not only amplifier gain (as it would be in a classic, generic description of a digital imager), it's a combination of amplifier gain, software processing in the raw->jpeg conversion, and maybe other stuff that varies depending on the specific camera model. CHDK overrides do not always control all of these elements successfully.

The point of this point  :-[ is that it shouldn't be a surprise when high ISO values are wonky. Specific cases should still be reported and fixed if possible, but in the end CHDK is hack and this is one of the hacky bits.
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In case, where is no change in the raw data, and the raw data is not overexposed, this can be corrected when you saving the RAW files and doing the JPEG processing on a PC or?
In cases like the D10, where the last stop is in JPEG, you might be able to recover images that were overexposed in the "ISO 1600" jpeg from raw. I'm not sure off the top of my head how this would work with rawopint. In general, I'd recommend keeping the ISO limits in the range that works normally.
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Offline MarkB

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #65 on: 02 / March / 2016, 00:12:23 »
Quote from: reyalp on 29 / February / 2016, 22:00:00
Quote from: MarkB on 29 / February / 2016, 19:30:27
I am happy to run the test, are there any specifications or parameters you need?  Or is just pointing the camera outside fine?

The subject should have constant, uniform lighting and not contain anything that moves. An LCD monitor showing a blank page or a blank wall under artificial light should be good.

Set the "ISO input type" to ISO, and enter the range of ISOs you want to test. For your test, you could just do something like 980 to 1020.

If you are only testing a small range like, you can set "Initial ev shift" to 0.

The other settings can be left default.

It's possible the "Shoot mode" setting will affect ISO override behavior.

Setting it  to "cont" and making sure continuous mode is enabled in the canon firmware should be most similar to your rawopint run that showed the funny ISO jump. If "quick" doesn't show the same behavior, you may be able to avoid the problem by turning off cont mode in rawopint.

edit:
FWIW, ISO overrides behaving oddly at high values is pretty common.  As mentioned in the first post, the last stop on some cameras is done entirely in JPEG processing, with no change in the raw data.



I did two tests on the s110 , in both the Canon firmware was set to Continuous Mode.  One test was set to "cont" in the script the second to "quick"
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Offline c_joerg

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #66 on: 02 / March / 2016, 04:33:13 »
 
Quote from: MarkB on 02 / March / 2016, 00:12:23
I did two tests on the s110 , in both the Canon firmware was set to Continuous Mode.  One test was set to "cont" in the script the second to "quick"
The results looking comparable to my camera. Both of your runs have not the same exposure time so there are not full comparable. But I looks like that the effect is independent from the exposure time, because I use 1s and you 0.05s.
It looks like; there is already an offset between ‘Cont’ and ‘Quick’ before ISO1000.
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Offline c_joerg

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #67 on: 03 / March / 2016, 13:13:47 »
I made another 4 runs with isoinc, just for interests. Every run gives a different result…
Combinations: Cont CHDK, Cont Script, Quick CHDK, Quick Script.
The script method of ISO settings avoids the JPG boost, but meter values going down.
For me it looks like, that there is still a real amplifier working, because meter increases in all cases.
If I understand the Dxomark ISO sensitive plot correct, then the real amplifier works until ISO6400 for the S110. But that might be a misinterpreting from my side
http://www.dxomark.com/Cameras/Compare/Side-by-side/Canon-PowerShot-SX50-HS-versus-Canon-Powershot-S110-versus-Canon-PowerShot-G1X___848_838_769
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Offline reyalp

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #68 on: 03 / March / 2016, 15:59:31 »
Quote from: c_joerg on 03 / March / 2016, 13:13:47
For me it looks like, that there is still a real amplifier working, because meter increases in all cases.
If I understand the Dxomark ISO sensitive plot correct, then the real amplifier works until ISO6400 for the S110.
I would interpret the "script" runs as the camera turning the real amplifier gain down by 1 ev, setting the jpeg process to add a constant +1 ev, and then running the amp through the range again. IIRC this is similar to one of the things we see on G1x, but G1x did it at much lower ISO.

The "chdk" ones look like the same thing happens initially, but then the -1 on the amp is lost. The ~half stop difference between cont and quick is just weird though  ???
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Offline c_joerg

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #69 on: 04 / March / 2016, 02:00:26 »
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I would interpret the "script" runs as the camera turning the real amplifier gain down by 1 ev, setting the jpeg process to add a constant +1 ev, and then running the amp through the range again.

May be…
But why does the cam do this so complicate? He could just go to the max real amplifier gain and add smaller steps to jpeg...
« Last Edit: 04 / March / 2016, 02:02:02 by c_joerg »
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