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

reyalp

philmoz
That seems to be the case - although the G1X is the only camera affected that I know if.

But only using CHDK script or overrides, right? If you set it all manually in the Canon UI, the jpegs would appear to have equal exposure.

The last stop of ISO on some other cameras is special, in some cases it can't be set using CHDK overrides, and if set in the UI only affects the jpeg, not raw values.

reyalp

Here's an updated version of the isoinc script.

Changes
Shooting method is now selected with the "shoot mode" mode option
Single: full half press and shoot cycle for each shot.
Quick: hold half press, click shoot full
Cont: continuous mode (errors if not also set in canon UI)

Changed "Initial ev shift": The sign was backwards before, now negative values mean less exposed.

Added an append to log option.

isoinc.lua

7.16KB

c_joerg

is it correct the Y axis is showing the brightness of the jpeg?

I think so. I do it in the following way:

Open JPG File.
Then I have a matrix form m * n *3 (RGB) with 8 bit data.
Then I calculate H = (R*0.3 + G*0.59 + B*0.11) for every pixel
Then calculate a mean value for all pixels.

So the value must be something like brightness. I know conversion from RAW to JPG is not linear, what you see on the y axis. In the same way, I analyzed overexpose on JPG, which is close to your results.

Single: full half press and shoot cycle for each shot.

Would be really interested, what this run shows ....

reyalp

So the value must be something like brightness.

Close enough for my purposes.

In the attached version of isoinc, I added an option called "ISO Set mode". If this is set to "Script" it will attempt to use the ISO override method Lapser suggested in https://chdk.setepontos.com/d/11081/84 for all shots after the initial value. This option is not valid in single shot mode, only quick or cont.

The basic difference from the C code is that it doesn't set the base ISO in SV_MARKET. This leads to some ambiguity, but it's worth a try since he was apparently able to get usable results with the G1x.

Setting to "CHDK" will use the normal CHDK overrides.

isoinc.lua

7.81KB

c_joerg

Made just a fast runâ€¦

I added an option called "ISO Set mode". If this is set to "Script" it will attempt to use the ISO override method Lapser suggested

This method is working definitely differentâ€¦. I think you getting close to a solution 😉
Well, thatâ€™s the difference between a Guru and a Jr. Member,
I wish I had the time to get your knowledge

The run was with r4138, continues mode and ISO set mode Script.
As you see, JPG is now OK 😀

isoinc_r4138_Cont_Script.csv

25.38KB

c_joerg

Meter96 has now a offset. Is this the blacklevel?

I get now a little bit confused about all combination which i can test.
Which combination can be helpful?
Still the single mode? With which release? And which ISO set mode?

reyalp

c_joerg
Meter96 has now a offset. Is this the blacklevel?

From a quick look, I think it's the behavior phil described in https://chdk.setepontos.com/d/12165/17

If you use the Canon controls to set the Av,Tv and Sv values in the region above the black point changeover it shoots at 1/2 the selected Sv and boosts the JPEG data to compensate (a DNG will be 1/2 as bright and show 1/2 Sv value in the EXIF).

Essentially when the ISO reaches 400, the camera drops the actual ISO (as seen in the raw data) back to 200 and boosts the jpeg. In continuous mode, it appears the black level change doesn't happen

Out of curiosity, what does the exif show for these?

I get now a little bit confused about all combination which i can test.
Which combination can be helpful?
Still the single mode? With which release? And which ISO set mode?

I would be interested to see the log from single mode, with CHDK ISO set.

c_joerg

Out of curiosity, what does the exif show for these?

EXIF was OK, so I have not posted it. I if you want, I can add the plot

I would be interested to see the log from single mode, with CHDK ISO set.

This method has one big disadvantage for timelapse. I this mode (which I use in my script) the camera always open the aperture for measure. This adds an aperture flicker. This is not happens with open aperture (may be also not with full closed aperture). So we will probably see this in the log fileâ€¦

https://www.youtube.com/watch?v=PVnqd4f3Kmk

Edit:
Add EXIF Plot

c_joerg

This is the run with r4138, single mode, with CHDK ISO set.

meter96 looks similar to the run from continues mode and ISO set mode Script.
EXIF ISO Data is correct (same as continues mode and ISO set mode Script)
JPG analyzing takes always time on my old PC...

isoinc_r4138_single.csv

25.46KB

c_joerg

I compare meter96 values from single and continuous mode (by normalizing before). There is a little bit more flicker in single mode, but not much. May be this depends that I used f16. A couple of month ago I compared my S110 in single mode (open aperture with f5.6). The differences were much bigger.

Also JPG looks similar.

So everything between the run from
'continues mode and ISO set mode Script'
and
'single mode with CHDK ISO set'
is the same.

reyalp

c_joerg
This method has one big disadvantage for timelapse. I this mode (which I use in my script) the camera always open the aperture for measure.

Understood, I'm not suggesting using it for timelapse, I'm just trying to understand the behavior of the G1x.

philmoz

reyalp

c_joerg
This method has one big disadvantage for timelapse. I this mode (which I use in my script) the camera always open the aperture for measure.

Understood, I'm not suggesting using it for timelapse, I'm just trying to understand the behavior of the G1x.

I've done a bit more experimenting.

When Tv >= 1.3s and ISO > 320:
- If ISO set manually in Canon settings
- black point = 2048 (in DNG, CR2 has black = 512)
- camera shoots at selected ISO
- max raw image value in DNG = 16384, in CR2 = 14847
- raw image values in CR2 file = raw image values in DNG - 1536 (2048 - 512)
- If ISO set using AUTO mode (Canon setting or CHDK override)
- black point = 2048 (in DNG, CR2 has black = 512)
- camera shoots at 1/2 selected ISO
- max raw image value in DNG = 16384, in CR2 = 16384
- raw image values in CR2 file = raw image values in DNG - 1536, then scaled up by some factor

So Canon is setting the sensor/ADC to a higher black point; but then fudging the raw data in the CR2 file to pretend the black is actually 512. When AUTO ISO is selected it also shoots at 1/2 the selected ISO and scales the raw image data to get the max value back to 16384.

I haven't found a point in the code where the raw buffer data has been changed - it's probably being on the Digic processor as the file is being saved.

It may be possible to 'compensate' for this behaviour in the raw meter - e.g. detect if camera is G1X, Tv >= 1.3s and ISO > 320, then adjust meter calculation. It would also need to take the calculated black point into account.

I have also seen some cases where the camera shoots at 1/2 ISO but with a black point of 512 - I have not determined the cases where this occurs yet.

Phil.

reyalp

philmoz
I have also seen some cases where the camera shoots at 1/2 ISO but with a black point of 512 - I have not determined the cases where this occurs yet.

This is seen in a couple of c_joerg's posts earlier:
https://chdk.setepontos.com/d/12165/26
https://chdk.setepontos.com/d/12165/29

In both of the above, Tv was 1.8 sec

The other kink in this is that the transitions don't seem to be at the same point: The 1/2 ISO seems to kick in at 400, while the black point does at 320. (edit: in the samples I've seen any way)

c_joerg

Made just a run on G1X with R4191 in continues mode and ISO set mode Script.
The run looks simular to r4138 (EXIF ISO OK, JPG OK).

isoinc_r4191.csv

25.18KB

reyalp

c_joerg
Made just a run on G1X with R4191 in continues mode and ISO set mode Script.
The run looks simular to r4138 (EXIF ISO OK, JPG OK).

Yeah, I think it's not really affected. It appears that the blacklevel jump at ISO 320 doesn't happen at all with these settings (it didn't happen in the r4138 run either). The ISO drop at 400 (compensated in jpeg) is still there, and would still cause problems for rawopint because even though the jpeg is OK, the raw meter value changes suddenly. It's possible a G1x specific workaround could be implemented in rawopint.

reyalp

Here's an updated isoinc.lua for trunk r4193.

Other changes:
* Added "ISO input type" If set to ISO, the start and end values are interpreted as Canon UI ISO. If set to SV96, they are interpreted as "real" SV96 values as in previous versions.
* More detailed logging.

isoinc.lua

8.51KB

c_joerg

A new run on G1X with R4193 in continues mode and ISO set mode Script would be useful?

reyalp

c_joerg
A new run on G1X with R4193 in continues mode and ISO set mode Script would be useful?

Both "script" and "CHDK" modes might be helpful. Thanks.

c_joerg

Iâ€™m getting more and more confused about stuff with G1X 😉
What about philmoz change in r4153? The still have an effect on this runs?
I make 3 runs with isoinc r4193 from sv96=520 until 740.
Iâ€™m not sure, if we had the combination quick/script beforeâ€¦

1) shoot_mode=cont / iso_method=script
2) shoot_mode=cont / iso_method=chdk
3) shoot_mode=quick / iso_method=script

I put â€˜*â€™ for ISO320 and â€˜oâ€™ for ISO400 in the plot from meter96.
Interesting is the run quick/script. There is an offset from around 16 which I have not seen beforeâ€¦

isoinc_r4193.csv

78.5KB

c_joerg

Iâ€™m wondering that EXIF ISO is for all runs OK.
I thought it must be wrong on the combination cont/chdk.
But the combination cont/chdk shows still the Â½ ISO kick on JPG data which I expect.

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