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

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Offline reyalp

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #70 on: 15 / March / 2016, 00:58:51 »
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From the g7x thread
Quote from: c_joerg on 14 / March / 2016, 06:02:29
For me it’s important the dynamic range of a camera. According DxO the dynamic range of G7x is 2EV better than the G1x.
It would be nice if you could start drtest.lua on the camera, and post the results.
Here's a drtest from g7x, along with one from d10 with the the same script version for comparison.

One notable differences is that for this particular scene (defocused on an LCD monitor showing a blank page), cameras idea of "correct" exposure is ~2/3 of a stop lower than the "neutral" value used in CHDK. On most other cameras I've tested, the m96 value is closer to 0. The d10 is almost exactly 0, but that's because it's the camera I derived the value from.

Another oddity of this camera is that the blacklevel seems to be about 511, not 127 as seen on other 12 bit cams. This is both from testing and what is appears in DNGs converted with Adobe DNG converter.

I'll do some isoinc runs later.
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Offline reyalp

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #71 on: 15 / March / 2016, 01:59:03 »
Here are isoinc runs on g7x from ~116-424 and 394-872

I'm not sure if the glitch at the start is a bug in port or the script, but aside from that it looks very linear.

Interestingly it seems to work even in the range below the 125 minimum.

These runs were all done in cont mode.

I also did a run at from ~800-6400, but the initial exposure value was bad (likely related to the first shot glitch seen in the others) and it ended up being over exposed. I'll try to run it again later, but it looked OK up to around 4000.
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Offline c_joerg

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #72 on: 15 / March / 2016, 05:06:10 »
 
Thanks for sharing this result with us.
I notice, that drtest logs m96 now in float and not in integer anymore….
If I understand the results correct, the G7x has 1 step more dynamic as the D10?

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Another oddity of this camera is that the blacklevel seems to be about 511, not 127 as seen on other 12 bit cams.[\quote]
That’s interesting for me that the cam made a higher dynamic range (12.7 EV) with a lower value range (511-4095). The G1x has (10,8) with a value range from 511 – 16383. Yes, that’s not just the bits from AD converter…

I’m not sure, how I can trust the following link:


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Here are isoinc runs on g7x from ~116-424 and 394-872 [\quote]
Have you seen any jumps in JPG results like on G1x?

Would be interesting to know, if the cam make also blacklevel jumps on exposure time > 1.3s.
May be you could try it with some values Tv >1.3s and higher ISO values.

Quote
One notable differences is that for this particular scene (defocused on an LCD monitor showing a blank page), cameras idea of "correct" exposure is ~2/3 of a stop lower than the "neutral" value used in CHDK. On most other cameras I've tested, the m96 value is closer to 0. The d10 is almost exactly 0, but that's because it's the camera I derived the value from.[\quote]
Interesting. How the JPG does look in that case (D10 to G7x)?
If I have m96 = 0 than the average on JPG is close to 128. Does the cam correct the 2/3 lower stop on the JPG processing?

One reason to do this is could be, that this protect the cam more for overexposure. The range from "neutral" to overexposure is larger. If you do this with another camera by setting it to -2/3EV and pushing it up in RAW processing, this gives you more noise. But maybe not on this cam…
« Last Edit: 15 / March / 2016, 05:08:48 by c_joerg »
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Offline reyalp

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #73 on: 16 / March / 2016, 02:38:32 »
I fixed a bug in the isoinc script that caused the initial ISO and exposure to be wrong in some cases. This probably happened in some of your runs too. Updated script attached.

I re-ran the isoinc tests on g7x. ISO seems to start at 115, and stay linear all the way up to 12800, with no jumps in the jpeg or funny stuff with the black level. All my runs have been with relatively short exposure times (all < 1 sec, and > 1/1000th for the highest ISO)

Quote from: c_joerg on 15 / March / 2016, 05:06:10
If I understand the results correct, the G7x has 1 step more dynamic as the D10?
It looks one more step of usable range to me, but the offset in neutral value makes it harder to compare directly.

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I’m not sure, how I can trust the following link:
[/l]
I don't know, my impression is their benchmarks are well regarded, but I don't see how g7x could have > 12 stops, since my test only covers 11 and has clipping at both ends.
It is interesting that their dynamic range chart for g1x DR is flat until around 400, then starts drop. The same point we see the blacklevel weirdness etc.
Quote
Interesting. How the JPG does look in that case (D10 to G7x)?
That's a good question. Just pointing them at the same blank monitor and letting them auto-expose, the g7x is a bit darker, average ~138 while d10 is ~147, but this wasn't a very scientific test.
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Offline c_joerg

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #74 on: 21 / March / 2016, 03:42:04 »
I was just playing with my IXUS160…
I made 3 isoinc runs (sv96 -> 400-600, 600-800 and 800 -1000) and drtest. Result attached in the zip file.
I thought the IXUS has only 10Bits but the results show me 12bits….

It looks like, that ISO works already <ISO100 but it stops exactly at ISO1600.
EXIF data is OK and works even with ISO6400.

But I see a small jump from 5 bits in the JPG Data around ISO560. It’s not much and you will not really see this when you only watch the JPG’s.

Quote from: reyalp on 16 / March / 2016, 02:38:32
with no jumps in the jpeg or funny stuff with the black level. All my runs have

Are you sure the JPG’s are OK on the G7x? How do you investigate this?

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Offline reyalp

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #75 on: 21 / March / 2016, 13:11:24 »
Quote from: c_joerg on 21 / March / 2016, 03:42:04
Are you sure the JPG’s are OK on the G7x? How do you investigate this?
Not completely sure, I just scrolled through the images, so I certainly could have missed smaller effects. I'm confident it doesn't jump a full stop or anything like that though.

Quote
I thought the IXUS has only 10Bits but the results show me 12bits….
Most cameras from 2009 or so have 12 bit raw.
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Offline c_joerg

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #76 on: 27 / March / 2016, 14:25:42 »
This is a full isoinc run with my G1x from ISO80 to ISO10000 (in 3 steps). As you can see, as long the exposure time is less than 1s the G1x make also no funny stuff.

There only two little jumps from '3' m96 values at ISO1600 and '6' m96 values at ISO3200. But this can be fixed at post processing.

Would be really interested what the G7x will do at longer exposure times…

I plan also for completeness this full runs with my SX230, S110 und SX50 in the next time…
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Offline c_joerg

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #77 on: 30 / March / 2016, 02:51:44 »
This is a full isoinc run of my SX50.

Every of my cams show other funny things. This is the first time where I see a plateau in the JPG data. It’s happen around ISO160, ISO750 and ISO 3600. But this will probably no trouble for time lapse.

M96 looks Ok until ISO 3600 where a jump from 1EV step is.
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Offline c_joerg

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #78 on: 09 / May / 2016, 04:26:34 »
Quote from: reyalp on 15 / March / 2016, 00:58:51
One notable differences is that for this particular scene (defocused on an LCD monitor showing a blank page), cameras idea of "correct" exposure is ~2/3 of a stop lower than the "neutral" value used in CHDK. On most other cameras I've tested, the m96 value is closer to 0. The d10 is almost exactly 0, but that's because it's the camera I derived the value from.
 

I’m not sure, if this is the same what I notice here:

I have quite a few Canon PowerShot models (G1x, S110, SX230, SX50) and a EOS1200D. And now for testing a g7x as well.

I hold the PowerShot models (without G7x) on a white wall with identical settings (Av mode with the same aperture, ISO, equivalent focal length ...), then I get on all models the same exposure time. Images are then all identical brightness and the histogram peak is in the middle. This works even with the IXUS500, when I then use the values from the EXIF for PowerShot.

In the DSLR that is different. Since exactly get half the exposure time. Even when G7x I currently this is so. Even with her you get half the exposure time (May be the 2/3 of a stop). Ultimately have these images have an identical brightness compared to the other power shots. Again, the histogram peak is located in the middle.


What insights can eventually win it? Is the EOS1200D and G7x around 1EV sensitive than the other power shots? So is ISO100 with the DSLR or G7x ultimately ISO200 on Powershot?


 

I again repeated the measurements yesterday, and must revise my statements above part.

Basically it is so that the light meter of EOS1200D and G1x tend (about 2/3 EV) to expose a little below. Probably about to have a little more dynamic upward.

On same manually settings, the pictures nearly the same.
« Last Edit: 11 / May / 2016, 03:54:43 by c_joerg »
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Offline c_joerg

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Re: Measuring exposure performance (was Re: proposal - script shooting hooks)
« Reply #79 on: 04 / February / 2017, 08:02:49 »
The results look funny from M10.

How did you run?

You should definitely do it in M Mode. The light should not change during the measurement.

The easiest way: Display a white area on a monitor and place the camera directly in front of it. The focus is not important.

A run from ISO 100 ... to ISO 400 would be interesting.
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