Physically Based

[evelyn]

From time to time I hear talk of "physically based" with Vray and others.
Since we most always use cameras to represent that reality can I ask for a psychological camera to be created instead of a physical one???? Our perception and the measures of Science are many times two different things. (Just made that up)

Evelyn

[RErender]

Hmm, you might be on to something, a "See art button" instead of a "make art button"

[evelyn]

Eric,

You miss the point. Have you ever rendered an interior/exterior scene with the camera inside and seeing outside and either the glass or the exterior is "blown out" as cameras do? What I would like is better exposure control that would approximate the human eye perception of illumination. A render like that would give a feeling of being there! If you have no use for something like that is ok. It is not about art but about a process being termed "physical" as in "real" when the judging of that reality is human perception and is not being represented as it sees it itself (assuming your average good eyes).

Evelyn

[RErender]

Ok, I see your point. Sorry for the bad joke. But I think it is already attainable.

[samuel_bubat]

Hi there,

A feature would be nice.. but you don´t really need it.
Exposure is nothing but a color correction in a High Dynamic Range
Environment. What you need is a tool that is able to read HDR, RPF or
OpenEXR formats in 96bit and offers a colorcorrection that also handles
96bit (pff... shame on photoshop) unfortunately.. so far I only know 2 tools
that are able to do this.
1. HDRShop in conjunction with Reinhards Tonemapping Plugin
wich is not very intuitive and where you don´t have a preview
but.. it works and it´s free as far as I know (for personal use).
2. Digital Fusion.. it´s very expensive but a dream of a program.

The exposure control itself is quite easy to handle.
Example Vray 1.09: Set color mapping to linear activate unclamped colors
in the G-Buffer Channels set the rendering output to RPF and activate
unclamped colors and 32bit per channel in the rpf dialog as well.
Add some photometric lights to your scene (IESSun ...)
and render the image (do not just hit f9 and save from the framebuffer
you must set the output before and render from the render button or
unclamped colors won´t be saved)
When you used a IESSun your image will probabely come out white.
That´s ok.

Now all you need to have full controll of your lightsettings are 3 parameters
gain, gamma, and saturation (no curves no Levels this should be added afterwards for final corrections)
I will describe it now with Digital Fusion.
Load your image into Digital Fusion (make shure DF defaults are set to 32bit per channel) and add a color corrector to your image.
Now decrease gain until every colorbleeding is removed and
hard shadows show proper antialiasing (might result in a very dark picture) Now use gamma to scale up your image again just so much until you like it. You will see that the picture now is very washed out.
Add a Color Gain filter and slighly increase the saturation until the colors
are restored.
That´s the main part.
If the picture is still to flat you can add another colorcorrection
after the main part. And now you can make last contrast adjustments
with curves or levels.
Keep in mind even 96bit is not infinite. In some cases there
can happen a colorbending when scaling up the image with gamma.

And now you have complete control over your lightenergy. You could
even animate those settings in Digital Fusion for example when you have
a flight from an indoor to an outdoor scenario. And it´s really easy to control.

Due to Digital Fusion is very expensive I would once more like to request
(whoever this may read)
a software that is just designed to do the steps described above.
It could be used with every renderer out there that can output unclamped
colors. Just input.. colorcorrection... output

here are some early example i made some years ago

linear lighting without exposure
[img]
http://sorceress.netfrag.org/optix/f.../fr_no_exp.jpg
[/img]


same with max logarithmic exposure
[img]
http://sorceress.netfrag.org/optix/f...fr_max_exp.jpg
[/img]


Rendered with a linear light energy and ballanced with digital fusion
as described above

[img]
http://sorceress.netfrag.org/optix/f...fusion_exp.jpg
[/img]

this was rendered with FinalRender some time ago but there is
no difference if you use Brazil or Vray or whatever ...

hehe.. I think this is the 3rd forum I posted this several times
but most people just seem to prefer "controll" by harming
multipliers in a physical incorrect way to avoid the "overbright windows
but to dark room" phenomenon. Tss.. life could be so easy

cheers

[evelyn]

Thanks Samuel. Very good information that you gave.

Evelyn