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Real vs market ISO

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Offline dvip

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Re: Real vs market ISO
« Reply #70 on: 20 / July / 2013, 22:38:34 »
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Did you have "test MIN-100 [.]" checked?

This crashes for me:

min ISO [80]
max ISO [3200]
half shoot delay [1000]
test MIN-100 [.]

This doesn't:

min ISO [80]
max ISO [3200]
half shoot delay [1000]
test MIN-100 [ ]

Could be that I didn't have "test MIN-100 []" unchecked ?
Running now 1.2.0-2968.
CSV file attached

« Last Edit: 20 / July / 2013, 22:50:27 by dvip »
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Offline reyalp

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Re: Real vs market ISO
« Reply #71 on: 20 / July / 2013, 22:54:09 »
Thanks. Phil confirmed the same thing in IRC.

The point of the script is to get the real and market sv96 values that correspond the the ISO values in the Canon menu. It's just a time saver compared to going through the menu and writing down the values manually. The fact that it crashes if you set the value outside of the Canon supported range isn't a problem.
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Offline reyalp

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Re: Real vs market ISO
« Reply #72 on: 21 / July / 2013, 00:53:40 »
I changed the CHDK override display to use "market" units, by converting the output of shooting_get_iso_override_value() back from "real". This leads to values that are usually 1 or 2 less than requested value, mostly (I think) due to integer divisions truncating.

I did this rather than just showing the input value because the override value can get clamped in shooting_get_iso_override_value(). There's much greater imprecision in the actual override process, but I imagine we will get a lot of questions about it if we leave it like this.

Another issue is with the "low" values. Since the current override code doesn't know about the special case for low values, having the correction actually ends up requesting an even lower override value than expected. On my D10, if I put in ISO 80, the canon UI flashes 64 when I half press because of this. Since ISO overrides don't actually work much lower than stock, this should only be a cosmetic issue, but I'm inclined to comment out the "low" special case for 1.2.
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Offline dvip

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Re: Real vs market ISO
« Reply #73 on: 21 / July / 2013, 11:26:42 »
@reyalp, thanks for 2972 update.
With the override set at iso 40, 80 and 100, I see a
small exposure difference. The only thing is that chdk always display iso 115
on the screen, and the jpg's exif is always set to iso 100... I'm sure you are still working on this.
The SX50HS has the same sensor and the min iso there is 80,
so it may be possible to get iso 80 with the SX40HS.
I hope Phil can also test this with his SX40HS.
 
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Offline reyalp

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Re: Real vs market ISO
« Reply #74 on: 21 / July / 2013, 14:33:58 »
Quote from: dvip on 21 / July / 2013, 11:26:42
With the override set at iso 40, 80 and 100, I see a small exposure difference
IMO, it is extremely unlikely that 40 is different from 80.
Quote
The only thing is that chdk always display iso 115
on the screen, and the jpg's exif is always set to iso 100...
You are saying the red CHDK override display shows 115 for 40, 80 and 100?

Quote
The SX50HS has the same sensor and the min iso there is 80,
Just to be clear, I am not changing the way ISO overrides actually work, only trying to make the input units approximately the same as what Canon shows on the screen.
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Offline reyalp

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Re: Real vs market ISO
« Reply #75 on: 21 / July / 2013, 16:28:39 »
A note on overriding ISO_MODE:

Phil noted that values between 80 and 100 (exclusive) crash SX40. On D10, they don't crash but the live view and image get a very strong red tint. This seems to be true for any value that isn't available in the UI, except for 50 and 64. However, 50 and 64 give identical exposure to 80.

The above is only relevant to ISO_MODE, regular CHDK ISO overrides use a different method.

edit:
On a540, the live view looks fine, but the result jpeg has the red tint.

edit:
A further note on OSD values. The "misc values" real and market ISO display does not match the override OSD, because it's based on shooting_get_iso_from_sv96 from the sv96 propcase. This should more closely reflect the value actually used, but is only updated after half press.
« Last Edit: 21 / July / 2013, 16:56:06 by reyalp »
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Offline reyalp

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Re: Real vs market ISO
« Reply #76 on: 21 / July / 2013, 17:42:16 »
Quote from: reyalp on 21 / July / 2013, 00:53:40
Another issue is with the "low" values. Since the current override code doesn't know about the special case for low values, having the correction actually ends up requesting an even lower override value than expected. On my D10, if I put in ISO 80, the canon UI flashes 64 when I half press because of this. Since ISO overrides don't actually work much lower than stock, this should only be a cosmetic issue, but I'm inclined to comment out the "low" special case for 1.2.
I made this change.
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Offline dvip

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Re: Real vs market ISO
« Reply #77 on: 21 / July / 2013, 20:31:13 »
@reyalp,
>You are saying the red CHDK override display shows 115 for
>40, 80 and 100?

Yes

>On my D10, if I put in ISO 80, the canon UI flashes 64
>when I half press because of this.

I don't get any UI flashes, just ISO 100 on the Canon UI, and ISO 115 in red (CHDK override display).


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Offline reyalp

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Re: Real vs market ISO
« Reply #78 on: 21 / July / 2013, 21:34:16 »
Quote from: dvip on 21 / July / 2013, 20:31:13
I don't get any UI flashes, just ISO 100 on the Canon UI, and ISO 115 in red (CHDK override display).
OK.

SX40 has
Code: [Select]
    #define CAM_MIN_ISO_OVERRIDE                70  // Defines min (non-zero) ISO override value - lower value may crash if flash used
in platform_camera.h

That is in "real" units. The override is limited to avoid going below this, and this is reflected in the value displayed.

Note that this should completely rule out lower values having any effect on exposure.

According to previous data, setting ISO 100 in the menu should result in a "real" ISO of about 60 (sv96 411, sv96_market 480). Using the standard conversion, real 70 = sv96 430, sv96_market 499 = ISO market 115.

You could try setting the define to 60,  which would correspond to the actual apparent minimum ISO, but I would expect that Philmoz based the 70 value on solid experiment (but it's possible the conversions have changed in the meantime, and 70 was meant to be a "market" value)

If you want to verify that 60 is OK, you should probably make sure you can reproduce the crash first, be removing the limit completely and verifying that it crashes with some low value.
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Offline dvip

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Re: Real vs market ISO
« Reply #79 on: 21 / July / 2013, 22:52:45 »
@reyalp,
I did a test with:

#define CAM_MIN_ISO_OVERRIDE                60

No crashes at iso 64 nor 80. Flash on or off.

And there is a exposure difference for sure between iso 64 and iso 100 (min for the SX40HS).
But I hope someone else can confirm this.

I get now iso 98 (CHDK override red display) when override iso 64 is used.

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