Equipment & Techniques > Beginner's Questions

Expose Right

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spassig:
Hello

I have read the article from Michael Reichmann about Expose Right.
I read the following statement.

Within the first F/Stop, which contains the Brightest Tones > 2048 levels available
Within the second F/Stop, which contains Bright Tones > 1024 levels available
Within the third F/Stop, which contains the Mid-Tones > 512 levels available
Within the fourth F/Stop, which contains Dark Tones > 256 levels available
Within the fifth F/Stop, which contains the Darkest Tones > 128 levels available

I don't understand this.
Why in this manner?

Why not in following steps.

Within the first F/Stop, which contains the Brightest Tones > 128 levels available
Within the second F/Stop, which contains Bright Tones > 256 levels available
Within the third F/Stop, which contains the Mid-Tones > 512 levels available
Within the fourth F/Stop, which contains Dark Tones > 1024 levels available
Within the fifth F/Stop, which contains the Darkest Tones > 2048 levels available

Regards

Jochen

bjanes:

--- Quote from: spassig on January 18, 2016, 05:45:38 am ---Hello

I have read the article from Michael Reichmann about Expose Right.
I read the following statement.

Within the first F/Stop, which contains the Brightest Tones > 2048 levels available
Within the second F/Stop, which contains Bright Tones > 1024 levels available
Within the third F/Stop, which contains the Mid-Tones > 512 levels available
Within the fourth F/Stop, which contains Dark Tones > 256 levels available
Within the fifth F/Stop, which contains the Darkest Tones > 128 levels available

I don't understand this.
Why in this manner?

Why not in following steps.

Within the first F/Stop, which contains the Brightest Tones > 128 levels available
Within the second F/Stop, which contains Bright Tones > 256 levels available
Within the third F/Stop, which contains the Mid-Tones > 512 levels available
Within the fourth F/Stop, which contains Dark Tones > 1024 levels available
Within the fifth F/Stop, which contains the Darkest Tones > 2048 levels available

Regards

Jochen

--- End quote ---

For an explanation of the number of tones in various levels, please refer to the linked chart posted by Norman Koren. The human visual system can visualize only about a 1% difference in tonal values (Weber-Fechner law), which corresponds to a about 70 levels per f/stop. In practice, more tones may be needed to prevent posterization if aggressive editing is applied to the image.

However, the number of tones is largely irrelevant with respect to ETTR as explained by Emil Martinec here. Emil points out that raw files are never posterized, since inherent noise dithers the levels.

Regards,

Bill

spassig:
@Bill

Thanks for quick feedback.
In the links are lot of information.
Hope it well answer my question.
I'm not sure

Jochen

Rory:
Hi Jochen

A camera determines brightness by counting photons, which are converted into electrons.  The reason the brightest f stop has the most information is because more photons were collected.  As you know, each f stop represents a doubling of the amount of light which equals a doubling of the number of photons.  So, arbitrarily starting with 128 photons:

f stop 1 = 128 photons = really dark
f stop 2 = 256 photons and 128 levels available to really dark levels f stop 1
f stop 3 = 512 photons and 256 photons/levels to previous stop 2
f stop 4 = 1024 photons and 512 photons/levels to previous stop 3
f stop 5 = 2048 photons and 1024 photons/levels to previous stop 4 and 4 times brighter than stop 1.

As you can see, each time you double the amount of light there is twice as much information (# of photons) compared to the previous double.  Consequently the darkest portions of the scene have the least information and are represented by the left side of a histogram.  The right side of the histogram represents the brightest portions of the scene and have the most information.  Hence the expression "expose to the right".

Of course, this is a simplistic example to illustrate the concept.  The links Bill posted will get you starting into the wonderful world of quantum efficiency, signal to noise, human vision ...

spassig:
@Rory

Thanks for your wonderfully explenation.

This will help me to compare it with analog photographie.

Jochen

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