Linear Tone Mapping does not make sense

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Linear Tone Mapping does not make sense

Postby tripleslash » Tue Jan 20, 2015 7:49 pm

Sorry for bothering you again,.. I don't want to be considered the new troll on the block!

From a photographers view "Linear Tone Mapping" does not make sense,

Film ISO does not reduce noise... render time does
Shutter speed does not reduce motion blur... most 3D figures stand perfectly still by nature
F-stop does not change the depth of field... It would be soo extremly cool if you could focus and change the DOF after the render is finished. but no
Gamma, is not really a parameter people are used to on a DSLR. but it works well.

ISO, Shutterspeed and F stop[1] all brightens the image in a linearly way and could be combined into a single bar called exposure. In which case there would be two bars and not 4, namely exposure and gamma.

Cheers

[1] Yes I know f-stop technically isn't linear mapped to the bar but it does not change the histogram values nonlinear like the gamma factor does,
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Re: Linear Tone Mapping does not make sense

Postby jeanphi » Wed Jan 21, 2015 2:33 am

Hi,

As you noticed the available parameters only act on the exposure, so yes they could in theory be mapped to a single parameter. However the whole point of that tone mapper is to give standard tuning knobs for the exposure so that if someone is accustomed to a given setting according to a given light setup, he won't play trial and error to find the correct tuning. Ditto if you want to insert some rendered objects in a real picture, it will be easier to match the exposure settings.
Nothing then prevents an exporter to link those parameters to the camera settings so that when you export, the DoF and motion blur will match the exposure settings. But that's a different thing.
Sure there are some post production refocus filters, but they are commonly available in picture editing tools so we did not find yet a need to include one in LuxRender. For motion blur, you will not be able to achieve a good result with post production filters, you need to start over the render if you're really serious about it.
For ISO, it could be linked to the noise threshold completion, there are even algorithms that describe ways to do it, but there's no free lunch, if you don't want noise you have to let it render longer.

Jeanphi
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Re: Linear Tone Mapping does not make sense

Postby tripleslash » Wed Jan 21, 2015 7:29 am

Thank you for the explanation Jeanphi.

I understand the point of exposure matching a real picture

I guess parallax movement, refocusing and DOF control would be possible after the rendering, like in the real world Lytro camera, since we probably know the light field.
https://pictures.lytro.com/

As far as I know the Lytro camera got its inspiration from 3D graphics.

In which case the FLM file should contain the ray's angle as well as it's spectral properties

Cheers
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