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Documentation: Color Management - formula formatting misleading / wrong
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Description

System Information
Linux Ubuntu 17.10, Firefox 59.0.2

Blender Version
Broken: 2.79 5bd8ac9abfa (but I am pretty sure it is related to the most recent documentation website version)
Worked: unknown

Short description of error
The documentation for the exposure value for the color management description has bad formating. It is unclear whether the exponent includes the value or not.
Here is the page:
https://docs.blender.org/manual/en/dev/render/post_process/color_management.html#settings

Exact steps for others to reproduce the error
Please visit the "Render" Headline here:
https://docs.blender.org/manual/en/dev/render/post_process/color_management.html#render
Then under "Exposure" there is a formula to calculate the final exposure value. It has however, formatting issues which make it unclear how the value is actually calculated. See my attached screenshot:

I would love to fix that myself, but I cannot make free time to research the correct formula at the moment (is it the one shown here? https://en.wikipedia.org/wiki/Exposure_value#EV_as_a_measure_of_luminance_and_illuminance). I will however, add this to my own todo as well and tackle this task once I find free time.

Thank you!

Event Timeline

The correct formula for calculating scene referred exposure adjustments is:

OUTPUT_VALUE = RENDER_INPUT_VALUE * (2^EXPOSURE_ADJUSTMENT)

As is frequently asked, the difference between the exposure adjustment in the Color Management panel versus the Film panel is that in the Color Management panel, the adjustment is applied solely upon the View, leaving the data untouched. The Film panel applies the adjustment to the data itself.

This is not clearly apparent as to the difference because Blender always bakes the view into the display referred formats. However, if one examines an EXR, one will see that the data itself is changed via the Film adjustment, while it remains as rendered when applied to the Color Management panel.

Hi @Troy Sobotka (sobotka),

Thank you for your informative answer.

The correct formula for calculating scene referred exposure adjustments is:
OUTPUT_VALUE = RENDER_INPUT_VALUE * (2^EXPOSURE_ADJUSTMENT)
[...]

So, as I understand it, the change I need to make is as follows:

From (sourcecode as reStructuredText: .rst ):

:math:`2^(stops) × value`

To:

:math:`value × 2^{(stops)} `

Before being able to fix the issue I would need to search for the proper file and the " × " symbol doesn't seem quite right when checking via the "Online Sphinx editor". But I will manage that once I check out the code on my machine instead of using the "show the source code" feature, for sure.

This is not clearly apparent as to the difference because Blender always bakes the view into the display referred formats. However, if one examines an EXR, one will see that the data itself is changed via the Film adjustment, while it remains as rendered when applied to the Color Management panel.

Aha, interesting. Would you say that the documentation should stress this difference?

`Btw., what source(s) are you using to support the mathematical background of your comment? Do you base it off only of a test .exr file? Lol, I guess not :D

Thank you!

Kind regards,

Adam

Philipp Oeser (lichtwerk) triaged this task as Normal priority.

Thx for spotting this.
I'll change this to TODO and assign @Aaron Carlisle (Blendify) , but @Adam Kalisz (blender_ei) : could you submit a patch like described here?

Philipp Oeser (lichtwerk) changed Type from Bug to To Do.May 2 2018, 10:29 AM

Thx for spotting this.

Thank you, it was not planned, but I thought that should be a quick fix.

I'll change this to TODO and assign @Aaron Carlisle (Blendify) , but @Adam Kalisz (blender_ei) : could you submit a patch like described here?

Great, thank you.
I have created a diff file:
https://developer.blender.org/D3196

I love how easy it is to contribute to the wiki. However, I am not sure about whether or not this formula is correct as I do not have any sources (only the comment by @Troy Sobotka (sobotka) . Furthermore the documentation mentiones the stops, which are not included in the new formula. So, this might need another revision from an expert. I am happy to incoorporate any changes in regard to that.

Kind regards,

Adam

Thanks I will have a look later.