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

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    This is the isoinc run with r4160 from sv96=520 until 740.

    The first 221 picture are made in single mode, the second 221 pictures are made in continues mode. The end of the run in continues mode is a little bit corrupted. But this was my mistake. I thought, the run was finished but still running.

    The logfile shows no differences between both runs.



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    This is the isoinc run with r4138 from sv96=520 until 740.

    The first 221 picture are made in continues mode, the second 221 pictures are made in single mode.

    There is a difference between both runs. The run in continues mode looks similar to the runs with r4160



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    Online reyalp

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    Also JPG analysing shows no differences on r4160 between both runs.
    As I mentioned before, philmoz change in r4153 only changes what CHDK thinks the black level is. It doesn't change the camera behavior at all. I am very sure of this.

    For isoinc, the only effect will be the meter96 value, because black level is part of the raw_to_ev96 calculation. It would also change the black level recorded in CHDK DNG files, if you have them enabled. That's all. For the rawopint script, the script is broken when the black level changes, because it has many calculations that depend on the value that aren't aware of the change.

    We need to understand the actual camera behavior. To avoid confusion due to the black level change, we can look at the meter column. This is the average of the raw frame buffer value, without converting into APEX96

    In the isoinc_r4160.csv from reply 10, in the first (non-continuous) run we see going from sv96 = 571 to 572, the meter value jumps from 789 to 2327. The "meter96" value doesn't jump, because this build is aware of the blacklevel change. In the second run (in continuous mode), there was no jump in the meter value.

    In the isoinc.csv from reply 12, we see exactly the same behavior. The only difference is in the meter96 value, which jumps because it is not aware of the blacklevel change.


    From this data, it looks like the black level change does not happen in continuous mode.

    In the "JPEG analyzing" (isoinc_r4160_JPG.png, isoinc_r4138_JPG.png ), is it correct the Y axis is showing the brightness of the jpeg? Or something else?

    The difference in jpeg EXIF ISO between continuous and not may be a clue, but I'm not sure what it means yet.

    One thing I'd like to see is if we get the same behavior using individual shots, releasing half press between each. I'll post a version of isoinc that supports this later.

    Philmoz noted a difference between script and override menu http://chdk.setepontos.com/index.php?topic=11081.msg121670#msg121670. These should be identical if the script override is set before starting halfpress, but in rawopint and the current isoinc, the override is set in inside the shooting process.
    Don't forget what the H stands for.

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    All of the runs above show a drop in meter value at sv96 = 603 (ISO=400)

    This also shows up in the in the timelapse from http://chdk.setepontos.com/index.php?topic=11081.msg122449#msg122449

    As you notice there, it only shows up as a momentary glitch in the raw data, but the jpeg seems to be jump in brightness after that. This appears to happen regardless of the black level change.
    Don't forget what the H stands for.

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    Offline philmoz

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    All of the runs above show a drop in meter value at sv96 = 603 (ISO=400)

    This also shows up in the in the timelapse from http://chdk.setepontos.com/index.php?topic=11081.msg122449#msg122449

    As you notice there, it only shows up as a momentary glitch in the raw data, but the jpeg seems to be jump in brightness after that. This appears to happen regardless of the black level change.

    At the point where the camera switches black point it is also changing ISO behaviour.

    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).

    If you use the CHDK controls (including scripts) it shoots at the selected Sv; but still boosts the JPEG image data resulting in a JPEG image that is 1 stop brighter.

    I don't know why, and I don't have a fix at this point.

    Phil.
    CHDK ports:
      sx30is (1.00c, 1.00h, 1.00l, 1.00n & 1.00p)
      g12 (1.00c, 1.00e, 1.00f & 1.00g)
      sx130is (1.01d & 1.01f)
      ixus310hs (1.00a & 1.01a)
      sx40hs (1.00d, 1.00g & 1.00i)
      g1x (1.00e, 1.00f & 1.00g)

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    At the point where the camera switches black point it is also changing ISO behaviour.
    It looks like there's two different points. In c_joerg's logs, the raw values and black level jump at sv96 = 572 (ISO 320) while the jpeg brightness jump happens at 603 (ISO 400)

    The first one doesn't appear to happen in continuous mode (at least if the initial values weren't already in the range that would trigger it), but the second does.

    With the isoinc script (with or without continuous mode) the drop in raw value seems to only affect the shot at ISO 400, before and after are normal:
    svsv96metermeter96
    397602851-269
    400603679-367
    401604852-269
    but all the jpegs after are boosted.
    Don't forget what the H stands for.


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    If you use the CHDK controls (including scripts) it shoots at the selected Sv; but still boosts the JPEG image data resulting in a JPEG image that is 1 stop brighter.
    I've been sort of following all this from a distance.  Until I read this.

    Does that in fact suggest that for any specific Tv, Av, & SV setting,  Canon also tweaks the JPG image differently afterwards?   So that if you linearly advance any one of those manually through its range (with a corresponding offset in one or both of the others)  you would not get the same JPG with each shot (ignoring motion blur and DOF) ?  The exposure would shift?

    I guess one f-stop of variance is not that big a deal on a P&S camera at the end of the day.  Post processing can deal with it easily.   (Unless you are trying for a smooth time lapse ...)
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    Offline philmoz

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    If you use the CHDK controls (including scripts) it shoots at the selected Sv; but still boosts the JPEG image data resulting in a JPEG image that is 1 stop brighter.
    I've been sort of following all this from a distance.  Until I read this.

    Does that in fact suggest that for any specific Tv, Av, & SV setting,  Canon also tweaks the JPG image differently afterwards?   So that if you linearly advance any one of those manually through its range (with a corresponding offset in one or both of the others)  you would not get the same JPG with each shot (ignoring motion blur and DOF) ?  The exposure would shift?

    I guess one f-stop of variance is not that big a deal on a P&S camera at the end of the day.  Post processing can deal with it easily.   (Unless you are trying for a smooth time lapse ...)

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

    Phil.
    CHDK ports:
      sx30is (1.00c, 1.00h, 1.00l, 1.00n & 1.00p)
      g12 (1.00c, 1.00e, 1.00f & 1.00g)
      sx130is (1.01d & 1.01f)
      ixus310hs (1.00a & 1.01a)
      sx40hs (1.00d, 1.00g & 1.00i)
      g1x (1.00e, 1.00f & 1.00g)

     

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