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naik
06-16-2010, 01:21 PM
Hey guys,

im quite sure that some of you know that issue when rendering as
a RGBA 32 Bit EXR or Tiff.

I got some "artifacts" in my rendering where some pixels in the reflection are
just white. Actually they are super white > 5.
When i render that scene to a normal RGBA ( 8 Bit ) those pixels
disappear and the rendering looks absolutely correct.

On the other hand i know that these pixels are just reflections of my scene where some materials colors or lights are over 1.0 - therefore this is the reflection.

But i can remember a "trick" to correct those pixels ...

Can anyone shed some light ?

cheers

naik

TaKIKO
06-16-2010, 02:13 PM
Try using the rayswitch for the materials with a value over 1. Just put a different texture or color with normalized values in the reflection slot and keep your original material in the default slot. On a side note are you rendering your reflection in separate pass? If so why not just give it a little tonemapping.

naik
06-16-2010, 02:31 PM
Hm i think i know what you mean.

But in another scene where i use the IBL with a hdr and a color gain over 1 ( 1.6 )
how would you do that?

TaKIKO
06-16-2010, 02:33 PM
With the ibl are you up'ing the color gain for illumination purposes? If so to correct your reflections theres a "Adjust Environment Color Effects" options in the render stats maybe try playing with that.

naik
06-16-2010, 02:35 PM
Also , in some situations you need to crank up the value in order to get
the desired result, wether its a self-illumnated material ( object)
or the reflection slot color white --> over white = 1.3 as an example...

And of course then you get the super white pixels i think...

cheers

naik

naik
06-16-2010, 02:59 PM
If so to correct your reflections theres a "Adjust Environment Color Effects" options in the render stats maybe try playing with that.

yep, i know that function, but why should that differ from the other
function in ibl node?

I can try this one, but im sure that this will not correct the white pixels...

TaKIKO
06-16-2010, 03:05 PM
When you render with the IBL with the color gain boosted what problem are you having. If it is the problem with the reflections what I am suggesting to try is when you boosted the color gain to increase illumination, I would pull the color gain down in the environments color gain to darken what is seen by reflections.

naik
06-16-2010, 03:13 PM
Perhaps another example.

Consider you have a scene plus an ibl but the color gain is set to 1.

Now you have an object with the car paint shader applied to it.
In the reflection tab you set the reflection edge weight to 3.

Therefore , if the material is highly reflective you will get the super white pixels at
some hard edges which is obvious.
When i set the value back to 1, i dont get those white pixels but
its not the desired look im after....


Now when leave the settings ( edge weight 3 ) and render my scene to
normal 8 Bit image - i have the desired result without the super white pixels
BUT of course its 8Bit ... so no EXR......

TaKIKO
06-16-2010, 03:32 PM
Ok i think i understand now. So EXR's can't be rendered out as 8 bit? Not sure this would fix your problem but in the framebuffer options check on "Desaturate".

Desaturate If a color is output to a frame buffer that does not have 32-bit (floating-point) and half-float (16-bit float) precision, and its RGB components are outside the range [0, max], mental ray clips the color to this legal range.

naik
06-16-2010, 03:50 PM
thanks again for you comments mate.

I mean the main benefit using EXRs is the fact that it is 32Bit capable including the
function that you can render several passes into one EXR.

So that would mean that i set the framebuffer back to 8 Bit and still using EXR
which is in my view not a real solution. I think you get what i mean.


I can remember that i had this issue several months ago.
So i rendered an image as 32Bit Tiff but i can also remember
that when i saved that one back to an 8Bit ( in Photoshop)
that this fixed that issue with the super white pixels.

But not this time :-(

Cuni
06-16-2010, 04:23 PM
I had the same problem as you, some time ago ... I had randomly pixels burned out, from reflexions. Using mia_materials, and EXR half float. At that time, I gave up, and I had to render the specular pass using maya software. I couldn't find a workaround at all.

naik
06-17-2010, 09:10 AM
I had the same problem as you, some time ago ... I had randomly pixels burned out, from reflexions. Using mia_materials, and EXR half float. At that time, I gave up, and I had to render the specular pass using maya software. I couldn't find a workaround at all.

Thats a pity mate....

I just dont get it, im quite sure there are plenty of other users with the same problem...

visua
06-17-2010, 09:45 AM
Read master zaps explaination here:
http://forums.cgsociety.org/showthread.php?f=87&t=543646

longrayjohnson
06-17-2010, 09:57 AM
i think one of the other guys said that already. render in passes and 32bit or half float Exr and use the colorcorrection functionality to bring down the superbright values and and then comp it together, buddy.

fdull
10-10-2010, 04:39 PM
very nice explanation by Zapmaster:
Read master zaps explaination here:
http://forums.cgsociety.org/showthr...p?f=87&t=543646 (http://forums.cgsociety.org/showthread.php?f=87&t=543646)

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