Author Topic: ETTR - exposure compensation stuck at +5 EV  (Read 3434 times)

ursamajor

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ETTR - exposure compensation stuck at +5 EV
« on: May 12, 2016, 05:50:47 PM »
Having ETTR activated I noticed that in Live View mode the exposure is corrected by +5EV compensation. Wtf, is this correct? And, unfortunatelly, the exposure compensation cannot be adjusted. Switching on Viewfinder mode, the exposure compensation (+5EV) remains, but, fortunatelly, it can be reset. It's a bug or it's a feature?  :D

a1ex

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #1 on: May 12, 2016, 07:41:46 PM »
Probably a bug - what camera?

ursamajor

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #2 on: May 13, 2016, 07:52:57 AM »
Canon 550D...

There are 4 settings for ETTR in its menu (http://www.magiclantern.fm/forum/index.php?topic=5693.0):
    Always On:  AETTR is always active.  In photo mode through the viewfinder, this means that AETTR is always inspecting the exposure in the image review, and setting the exposure settings for the next shot.  In Live View, this means that AETTR is always looking at the image in the live view, and adjusting the exposure settings as necessary.
    Auto Snap:  After taking a shot, AETTR will take another shot if necessary.
    Press Set:  AETTR activates by pressing the SET button.  In photo mode through the viewfinder, AETTR will turn on live view, determine the correct exposure settings, and return to photo mode.  In live view modes, AETTR will determine the correct exposure settings.
    HalfS DblClick:  This functionality is exactly like Press Set above, except the trigger button is half pressing the shutter button twice.

Now, reading from above, I believe I was a little n00b.  ;D Still, the exposure compensation (+5EV) made by ETTR is way too much.

a1ex

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #3 on: May 13, 2016, 08:08:24 AM »
http://support-sg.canon-asia.com/contents/SG/EN/8200743300.html

Quote
The compensable range is within ±5 stops in 1/3-stop increments.[

=> not a bug. It's just ETTR conflicting with Canon meter - one more reason to disable ETTR in automatic modes.

http://www.magiclantern.fm/forum/index.php?topic=12579.msg121155#msg121155
http://www.magiclantern.fm/forum/index.php?topic=5200.msg114522#msg114522

ursamajor

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #4 on: May 13, 2016, 08:48:18 AM »
Indeed I used Av mode. I couldn't (re)set exposure compensation, I know how to do it. ;) After reading the first linked post, I understood that this is the behaviour of ETTR on Auto modes. I'll switch on M to see if it works. I'll keep you posted.

Thank you very much for replies, really helped me.  :)

a1ex

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #5 on: May 13, 2016, 08:54:03 AM »
Hm, so exposure compensation actually got stuck, so you couldn't dial it down normally? This could indicate a problem in the backend, but limit checking code looks OK.

May I ask what ML version?

ursamajor

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #6 on: May 13, 2016, 09:06:51 AM »
Yes, exp. comp. got stuck.
It was last nightly build, 2016 May 07, I think.

ursamajor

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #7 on: May 13, 2016, 02:09:41 PM »
OK, I made some tests to see how ETTR works on my Canon 550D.
I put the ETTR "Always ON", switched to Manual mode (read that only in this mode it works properly) and... nothing happened. I tried to take pictures in different lightened scenes, still nothing. So, in M mode ETTR doesn't make any adjustement.
Switched to "Av mode" just for checking. Something happened here, but the mode of compensation of exposure seemed to me... chaotic, not at all consistent: sometimes compensation was +2/3EV, sometimes -1, TO THE SAME SCENE, just after press half shutter.
All of these work ONLY IN LIVE VIEW mode, they don't work in Viewfinder mode.
The camera don't use the minimum shutter speed set...
Where am I wrong or what it is wrong to this build from 2016 May 07?

My ETTR settings are... see picture bellow:



a1ex

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #8 on: May 13, 2016, 02:21:28 PM »
Check the main menu for ETTR (not the submenu) and write down the help text.

mario1000

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #9 on: May 13, 2016, 03:09:30 PM »
Dear A1ex,

may I ask another question concerning ETTR during filmimg?

I set ETTR triggering to the SET-button.
When I start filming (RAW not MLV) with mycamera (5D3.113 with latest nightly build) I am able to apply ETTR only one time (e.g. changing from a very bright to a very dark scene): after pressing the SET button I get a very decent result but when I try to press the SET button a second time nothing happens, i.e. the exposure stays the same after pressing the SET button. Is this an intended behaviour?

BR

ursamajor

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #10 on: May 13, 2016, 03:36:34 PM »
Do you mean this menu? I set only minimum exposure time/slowest shutter and let the rest as default. Took pictures in varied scenes: high DR, normal DR etc. Should I modify some settings? Is there an ETTR guide somewhere? I already read 2-3 threads but nothing clear, just some examples/samples.

What's the difference between this AETTR and manual ETTR by exposure compensation, excepting automation?


a1ex

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #11 on: May 13, 2016, 03:51:51 PM »
This is the submenu - go back one level and check the help text you see there. If anything else needs to be configured, that help text will tell you so. This was clearly the case for your first screenshot, but I'm not 100% sure about the second one.

Guides:
http://wiki.magiclantern.fm/ettr
http://www.magiclantern.fm/forum/index.php?topic=5693.0

ursamajor

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #12 on: May 13, 2016, 04:18:57 PM »
Back one level it is Exposure menu. No ETTR menu independently.
ETTR appears as submenu in Expo Menu and in Triangle Menu. What I don't understand is why ETTR appears in gray as it wouldn't be active, although under this gray color it appears as ON (see pictures bellow). Is there a reason for that?



a1ex

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #13 on: May 13, 2016, 04:37:16 PM »
Right there. Move the cursor on ETTR and read the help.

Write it down here.

ursamajor

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #14 on: May 13, 2016, 05:52:51 PM »
Enable image review from Canon menu. written with orange. Is that necessary for ETTR to work properly? I deactivated this function because usually I don't need to review my pictures.
I activated it.
Mode M, Viewfinder/Live View: I took an underexposed picture (as asked) then camera beeped and the exposure for the next pics was the same, not at all exposed to the right. Pictures taken to a normal DR scene (outdoor series).
When I took pictures to a higher DR scene (my monitor in a dark room, indoor series), it took first pic at 100 ISO, then increased to 400 ISO at the second pic and to 800 ISO for the next pics... Noticed that last exposure (at 800 ISO) had some clipping on highlights, making it unusuable in a certain degree.

Is this the workflow: taking first underexposed picture then expect to take the second (third etc.) with ETTR?
Thank you very much for your patience, benevolence and your kind availability!  :-*



a1ex

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #15 on: May 13, 2016, 06:06:11 PM »
Can you include the raw histogram in the screenshots?

ursamajor

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #16 on: May 13, 2016, 06:11:03 PM »
How to? Histogram from Lightroom? Or from the camera? In that second case I must reload RAWs on the SD card, I already transferred on HDD. :D
Or read it with another software... it was a link in one thread.
EDIT: RAW Digger... I'll install it and made asked corrections in the collage.

dmilligan

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #17 on: May 13, 2016, 06:21:36 PM »
(my monitor in a dark room, indoor series)
In low light (i.e. high noise) situations ETTR will clip highlights to maintain the requested midtone and shadow SNR limits. To disable this, simply turn the SNR limits off in the ETTR submenu.

a1ex

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #18 on: May 13, 2016, 06:22:27 PM »
Any kind of raw histogram should be fine.

The one from ML is best because ETTR makes the exposure decision from there. You can repeat the experiment, enable the raw overlays in QR, and use Debug->Screenshot before each picture.

ursamajor

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #19 on: May 13, 2016, 06:36:33 PM »
In low light (i.e. high noise) situations ETTR will clip highlights to maintain the requested midtone and shadow SNR limits. To disable this, simply turn the SNR limits off in the ETTR submenu.

Thank you for idea!

Look the histograms. The 2nd and 3rd pictures from outdoor have virtually the same histogram, that's why I attached only the first screenshot of histogram to the collage.

In low light (i.e. high noise) situations ETTR will clip highlights to maintain the requested midtone and shadow SNR limits. To disable this, simply turn the SNR limits off in the ETTR submenu.


ursamajor

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #20 on: May 13, 2016, 06:48:26 PM »
Quote
In low light (i.e. high noise) situations ETTR will clip highlights to maintain the requested midtone and shadow SNR limits. To disable this, simply turn the SNR limits off in the ETTR submenu.

I disabled both, but now ETTRight became ETTLeft. Underexposed to maximum of 1/4000 s.  :'(

a1ex

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #21 on: May 13, 2016, 07:00:36 PM »
For the outdoor image: the white level for your camera is about 13255 DN above black level (from indoor histograms).

The outdoor histogram has its max level at around 5900, and if you ignore the brightest 0.5% pixels, it will be probably around 5000. So, your image is about 1.5 stops underexposed.

Note the exposure target was set to -1 stop, so the difference was really less than 0.5 stops. Without knowing more about the exact settings used, and without seeing the metered raw histogram, I can't tell why this difference wasn't corrected (there are many possible cases).

For "ETTLeft": you probably have a specular highlight in the image (or maybe even a large group of hot pixels), so ETTR probably metered for that. Without seeing the raw histogram, I can't give an accurate answer.

ursamajor

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #22 on: May 13, 2016, 07:39:06 PM »
I understood, I'll try to increase the target exposure to see what's happen.

Look the photos and correspondent histograms with both SNR OFF.
As far as I understand ETTR sometimes can become ETTL. If the purpose of ETTR is to limit the noise, ETTL is far from this from my point of view. Of course, I understand, there are limits that ETTR/ETTL cannot transgress. Still I believe that  it'll be very usefull some hints for settings in a manner to help in most common situations.
Anyway, you were so kind and that's why I thank you one more time! I'll use my week end for experiments, especially now after changing my focusing screen.  :D
I wish you a good night and a nice week end!


a1ex

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #23 on: May 13, 2016, 07:48:41 PM »
In that case, you can try increasing highlight ignore.

If you are looking to reduce noise, SNR limits are your best friend (because the exposure decision is made from... guess what... measuring noise levels). But this may give clipped highlights in HDR scenes.

If you want both low noise and good highlight detail in HDR scenes, try dual ISO.

ursamajor

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #24 on: May 13, 2016, 08:04:38 PM »
Quote
If you want both low noise and good highlight detail in HDR scenes, try dual ISO.

It was the next step I wanted to ask: to have ETTR + DualISO it's absolutely necessary to activate DualISO or it's enough to select "linked to DualISO" in ETTR submenu, so that I can have ETTR+DualISO only when I activate ETTR? Sincerly, I don't like to have active DualISO all the time, because at primary high ISOs I get many hot pixels. By the way, what version is the DNG file obtained from cr2hdr software/plugin processing of CR2s files? I noticed that my DNG v. 1.3 from CHDK installed on my compact are hot pixels free. On the other hand, the v. 1.0 had tons of hot pixels. Just an idea...

a1ex

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #25 on: May 13, 2016, 08:16:35 PM »
Yes, enable both.

In general, Dual ISO works best if the base ISO is 100, and the recovery ISO is higher (400-1600). The reason for that is buried somewhere in this thread: www.magiclantern.fm/forum/index.php?topic=10111

exiftool image.DNG -dngversion, but it won't help with hot pixels (I'll let you figure out why).

At what ISOs do you get hot pixels that can't be corrected by cr2hdr?

ursamajor

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Re: ETTR - exposure compensation stuck at +5 EV
« Reply #26 on: May 13, 2016, 08:37:43 PM »
If primary ISO is 1600 ISO I get very few hot pixels and too many at 3200 ISO. But 3200 it's already too much, I used it just for experiments. :)
Anyway Dual Iso has stunning results.