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The new two-stage auto ISO function - some facts & questions

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Offline msl

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The new two-stage auto ISO function - some facts & questions
« on: 09 / August / 2012, 16:31:27 »
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@tsvstar has provided improvements for the user auto ISO function.

http://chdk.setepontos.com/index.php?topic=7284.0

This improvements were tested and found to be good by two guys, which work more in the 'underground'. They had also developed the GPS stuff for the SX230.

The result was a merged patch, which was added in CHDK-DE (changeset 932). Through the merging of CHDK and CHDK-DE was this features also added to CHDK.

That's the reason for this:

@reyalp wrote:
Quote
Even more ranting:
the defines USE_REAL_AUTOISO and OVEREXP_COMPENSATE_OVERALL are only set for sx230. This does not seem to be due to any special characteristics of that camera. If the option is actually better, then we should use it everywhere. If it's not, then we shouldn't. If there is value in each option, then we should make it a run time option.
( http://chdk.setepontos.com/index.php?topic=8213.msg86427#msg86427 )

Now are the questions:

Should we define USE_REAL_AUTOISO and/or OVEREXP_COMPENSATE_OVERALL for all cameras?

Need we the definition OVEREXP_COMPENSATE_OVERALL really? (Canon Overexposure exists only at daylight.)

Can someone (@tsvstar) explain the two-stage functions understandable?

msl
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Offline msl

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Re: The new two-stage auto ISO function - some facts & questions
« Reply #1 on: 25 / August / 2012, 10:10:35 »
Push ... (sorry)

Any thoughts?
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Re: The new two-stage auto ISO function - some facts & questions
« Reply #2 on: 25 / August / 2012, 10:36:21 »
Did you try PM'ing tsvstar ?  Its a pretty obscure bit of functionality without a more detailed explanation to follow.
Ported :   A1200    SD940   G10    Powershot N    G16

Re: The new two-stage auto ISO function - some facts & questions
« Reply #3 on: 05 / July / 2013, 15:07:18 »
I've made an attempt to start documenting the new Custom Auto ISO for the 1.2.0 user guide. 

http://chdk.wikia.com/wiki/CHDK_1.2.0_User_Manual#Custom_Auto_ISO

Before we lock down 1.2.0 as the stable trunk,  I'd like to do some cleanup of this function & its UI so I thought I'd re-open this thread.

First of all, to answer msl's question from above,  there are basically two changes to this module vs the old code :
  • there is an additional [minimum shutter speed & maximum ISO pair] added - to be used when the camera cannot keep the ISO & Tv setting within the original range
  • there are three new "exposure" compensation parameters that look at the histogram for the scene and allow you to specify a fixed exposure offset if a user defined number of pixels exceeds a user defined exposure threashold



Simple items to be cleaned up :
1) Max ISO HI (x10) menu item is in the wrong place - should be below Max ISO Auto
2) Delete the word "Second" from two menu lines - it should be just "Alternate Min Shutter Speed" and "Alternate Max ISO" -  the word second is redundant and it makes the menu lines too long for my cameras
3) ISO menu items that accept numeric values as (x10) are confusing. Just use regular numeric inputs.  Or better still an enum'd range of choices.

More Interesting Questions :
1) The SX230, SX240 and SX260 seem to interpret the menu ISO values as "real" ISO value.  All other cameras treat the menu entries as "Market" ISO and do a nasty hack to convert them to "real" ISO.  This makes no sense - it should be one way or the other and the default for CHDK is usually "real" value AFAIK.
2) Similarly,  the SX230, SX240 and SX260 handle the exposure compensation differently.  From what I can tell,  they apply the compensation in all situations.  Other cameras only do so in "day light mode" - which seems to be defined as the ISO value not being at one of the upper limits.  Again, why are those three cameras different.
3) Finally, why is the whole exposure compensation mechanism embedded in the AutoISO menu?  Its more like a tweak to "P" mode that just happens to get enabled when you enable AutoISO.

Comments?
« Last Edit: 05 / July / 2013, 15:18:06 by waterwingz »
Ported :   A1200    SD940   G10    Powershot N    G16


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Offline msl

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Re: The new two-stage auto ISO function - some facts & questions
« Reply #4 on: 05 / July / 2013, 15:49:33 »
Difficult topic, thanks for your efforts.

-clean up:

1. agree.

2. In the German version I use '2.' instead 'second' because of the line length. For a better understanding you could name the two stages: '1. stage min. shutter speed' and 2. stage min. stutter speed', or something like that.

3. agree.

-more questions:

I think, SX240 and SX260 are a result of the SX230 as reference for porting. The 'underground' guys (see my first topic) have made their own thing. Nobody understands this because there is no description.

The 'real' ISO should be the base for the calculation. This three cameras should be changed so that they operate uniformly as all other cameras.

msl
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Offline reyalp

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Re: The new two-stage auto ISO function - some facts & questions
« Reply #5 on: 05 / July / 2013, 15:50:34 »
1) The SX230, SX240 and SX260 seem to interpret the menu ISO values as "real" ISO value.  All other cameras treat the menu entries as "Market" ISO and do a nasty hack to convert them to "real" ISO.  This makes no sense - it should be one way or the other and the default for CHDK is usually "real" value AFAIK.
Agree it should be one way or the other. If the code to use "market" ISO is correct and portable, it would be great to use it everywhere. If it's not, then everything should just use real. Having different cameras randomly treat units differently is just wrong.

Quote
2) Similarly,  the SX230, SX240 and SX260 handle the exposure compensation differently.  From what I can tell,  they apply the compensation in all situations.  Other cameras only do so in "day light mode" - which seems to be defined as the ISO value not being at one of the upper limits.  Again, why are those three cameras different.
Again, weird hard coded differences for specific models (that don't depend of underlying capability of the platform) are wrong, and should go away.

Quote
3) Finally, why is the whole exposure compensation mechanism embedded in the AutoISO menu?  Its more like a tweak to "P" mode that just happens to get enabled when you enable AutoISO.
Good question  :-[
Don't forget what the H stands for.

Re: The new two-stage auto ISO function - some facts & questions
« Reply #6 on: 05 / July / 2013, 15:52:19 »
The 'real' ISO should be the base for the calculation. This three cameras should be changed so that they operate uniformly as all other cameras.
Curiously, the three rogue cameras are using real ISO.  The way its written,  all the other cameras assume market ISO is what is entered in  the Custom Auto ISO menu and then convert to real ISO using a straight line linear approximation.
Ported :   A1200    SD940   G10    Powershot N    G16

Re: The new two-stage auto ISO function - some facts & questions
« Reply #7 on: 05 / July / 2013, 15:55:48 »
If the code to use "market" ISO is correct and portable, it would be great to use it everywhere
From what I can tell,  its an approximation based on testing it with one camera (S90).  I believe you have posted in the past that the conversion is different from camera to camera and not linear ?

Otherwise,  it would be a great project to sneak in just before the version jumps.  But I don't think its going to be possible?
Ported :   A1200    SD940   G10    Powershot N    G16


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Offline msl

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Re: The new two-stage auto ISO function - some facts & questions
« Reply #8 on: 05 / July / 2013, 16:04:28 »
Curiously, the three rogue cameras are using real ISO.  The way its written,  all the other cameras assume market ISO is what is entered in  the Custom Auto ISO menu and then convert to real ISO using a straight line linear approximation.
What i meant, all ISO inputs should be 'real' ISO values like the ISO override or bracketing function.

msl
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Re: The new two-stage auto ISO function - some facts & questions
« Reply #9 on: 05 / July / 2013, 16:16:04 »
Curiously, the three rogue cameras are using real ISO.  The way its written,  all the other cameras assume market ISO is what is entered in  the Custom Auto ISO menu and then convert to real ISO using a straight line linear approximation.
What i meant, all ISO inputs should be 'real' ISO values like the ISO override or bracketing function.
Agreed.  It should be consistent across all menus & functions.   And as reyalp has pointed out - there is not currently a way to convert market to real that can be applied to all cameras (other than upgrading the iso_table[] in every camera's shooting.c file and then getting the values from every single camera  or  finding a new function in the firmware that does that for us).
Ported :   A1200    SD940   G10    Powershot N    G16

 

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