Author Topic: Understanding ETTR diagram  (Read 6873 times)

Theiamania

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Understanding ETTR diagram
« on: July 22, 2015, 12:26:36 PM »
Hi guys,
I'm starting to use ETTR exposure methid on my canon 60D.
I'd like only to understanding ETTR diagram displayed on monitor. Sometime the the RGB balls become bigger/smaller...  ???and sometime compare number inside these balls...  :o
What does it mean?
I didn't find this explanations on web, but tons and tons disputes and quarrels on use or not use ETTR  :D :D :D

Many, many thnaks for a reply!


vertigopix

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Re: Understanding ETTR diagram
« Reply #1 on: July 22, 2015, 12:30:22 PM »

Theiamania

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Re: Understanding ETTR diagram
« Reply #2 on: July 22, 2015, 02:43:55 PM »
Okay v,
thx for your reply.
So, If I have rightly understand:
1 - you start to exposure on right increasing aperture (for video). Than ETTR histogram shows all three R G B  increasing their dimension till a full circle: this should be the correct/suggested ETTR exposure.
2 -if you increase more your exposure, R G B full circles show a number inside,  circles show a number to them, which means that you're in overexposure, quantifying every single overexposure value inside every single RGB channel in EV +1, +2... so + 1 stop, + 2 stop...
Am I right? ??? ??? ??? ???


Theiamania

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Re: Understanding ETTR diagram
« Reply #3 on: July 23, 2015, 09:30:52 AM »
Anybody use ETTR...? :o

Walter Schulz

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Re: Understanding ETTR diagram
« Reply #4 on: July 23, 2015, 09:40:11 AM »
If there are things unanswered/incorrect in given link someone will most likely trying to help.

garry23

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Re: Understanding ETTR diagram
« Reply #5 on: July 23, 2015, 10:17:24 AM »
@Theiamania

This may help you.

Look at ETTR as a kind of 'auto' mode on your camera.

You decide the aperture, ie for artistic or DoF reasons.

You initially set the ISO to the lowest, eg ISO 100.

You decide the slowest acceptable shutter speed, ie for hand holding reasons. If on a tripod this can, according to to your artist vision, be very low, ie eg as low as, say, 30s.

The ETTR will then decide the shutter speed to meet two criteria: the exposure will be shifted to the right of the histogram to meet your clipping setting and, if required, your ISO will be adjusted to meet your min shutter speed.

ETTR means you will get a very 'over exposed' looking image compared to 0Ev metering, say, You must post process.

You can then build on the above by also linking in Dual-ISO. But I would recommend you get used to basic ETTR first.

Set the ETTR setting to 0, ie clipping, and the two SNR setting.

If you change these you will get some clipping, which of course is acceptable in some cases.

I have tried to write about ML on my blog and you are most welcome to look here: photography.grayheron.net. But I'm only an amateur so don't think I'm a guru on ML. like others that post replies :-)

Theiamania

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Re: Understanding ETTR diagram
« Reply #6 on: July 23, 2015, 01:58:10 PM »
Hi garry,
many thanks for your reply, but I asked something really different... ::)

Theywere two simple questions,only to know if I've rightly understand the meaning of RGB circles. Sorry, but maybe I have to repeat me:

1 - you start to exposure on right increasing aperture (for video). Than ETTR histogram shows all three R G B  increasing their dimension till a full circle: this should be the correct/suggested ETTR exposure.
2 -if you increase more your exposure, R G B full circles show a number inside,  circles show a number to them, which means that you're in overexposure, quantifying every single overexposure value inside every single RGB channel in EV +1, +2... so + 1 stop, + 2 stop...

Anyway, I doesn't touch change  ISO I decided to use (always as low as possible) and I stay always on 180 shutter degree rule, apply any temporal FX in post. The only parameter I change to exposure is Aperture. 

I mean, right now I'm starting to understand how exposure in ETTR with ML to capture more Dynamic Range as possible for post. No way (and no time...  :-[) in this moment to experiment.

I'll visit ypur blog, of course and again, thanks for your reply, but sorry, I asked something other...  ???
 


garry23

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Re: Understanding ETTR diagram
« Reply #7 on: July 23, 2015, 03:02:37 PM »
This page tells you everything: http://wiki.magiclantern.fm/ettr

Theiamania

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Re: Understanding ETTR diagram
« Reply #8 on: July 23, 2015, 03:24:08 PM »
I already read this page, of course...!
It is not so clear about what I asked, and sincerely, I'm not surprise now, cause nobody still can not answer to my very elementary questions... :-\
Anyway thanks for your reply!
 8)

garry23

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Re: Understanding ETTR diagram
« Reply #9 on: July 23, 2015, 03:36:58 PM »
Ok. Apart from this, you're on your ;-)

Using the histogram

Inside this histogram you may see near the top-left of the graph, in white lettering, the letter E followed by a number which represents how far you can go, in EV numbers, to reach ETTR, i.e E1.2

Inside the RAW histogram near the bottom you may see colored circles with numbers inside which represent the overblown channels (R, G, B) and the number of EV of over-exposure. To see this aim to an area with higher more light and take a pic.

Theiamania

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Re: Understanding ETTR diagram
« Reply #10 on: July 23, 2015, 04:05:46 PM »
Okay garry, now you are in focus about the argument!

But sorry, you have repeated the same words I used... :-[


1 - you start to exposure on right increasing aperture (for video). Than ETTR histogram shows all three R G B  increasing their dimension till a full circle: this should be the correct/suggested ETTR exposure.
2 -if you increase more your exposure, R G B full circles show a number inside,  circles show a number to them, which means that you're in overexposure, quantifying every single overexposure value inside every single RGB channel in EV +1, +2... so + 1 stop, + 2 stop...

So, I think, I can push up exposure till the three circles, first, become VISIBLE, and second, when they are BIG, I reach the maximum right exposure available, before clipping. That's all!
A many cases, you can push up just  a little more right exposure... to work with in in post. In this cases, inside the BIG circles (RGB channel) appear numbers, which minds +1 EV stop, +2 EV stop,...  in over exposition.
I don't see any others meaning about it... :-[

Kharak

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Re: Understanding ETTR diagram
« Reply #11 on: July 24, 2015, 05:34:47 PM »
The way you explain it, theiamania. Is how I have been using it. I think it is the correct way.
once you go raw you never go back

Audionut

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Re: Understanding ETTR diagram
« Reply #12 on: July 25, 2015, 07:48:58 AM »
http://www.magiclantern.fm/forum/index.php?topic=12096.0#post_Histogram

Quote

[snip]
The colored circles in the histogram, warn of overexposure in the color channel.  Small circles show a very small amount of exposure, with the circles increasing in size.  When at least 1 % of the pixels of a channel are overexposed, the numbers inside these colored circles, describe the percentage of pixels that have been overexposed in that color channel.  In the above example. 1% of red pixels have been overexposed, 10% of green pixels and 2% of Blue pixels.
[/snip]


Theiamania

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Re: Understanding ETTR diagram
« Reply #13 on: July 26, 2015, 06:52:11 AM »
Hi Audionut,
in your link, FINALLY, we can simply and rightly understand how Histogram (and ETTR) works. Great!

Many thanks for all reply, of course.   ;D