Re: (*.hdr) environment shader questions

["Tim Leydecker" <BauerOink(at)gmx.de>]

Hi Luc-Eric,

thanks for pointing out the manual, will give it another go :-)

So, as far as I get it, when my renderregion changes the
moment I "enable effects" on the environmentshader ´s
image "Adjust" page, this is due to the display gamma
setting of the renderregion. I´ll check my preferences
settings.

When I asked about the 8-16bit conversion I expected
it to be a convenience hack for using lowdynamicrange
images as the input for lighting calculations of FG.
Didn´t realize it´s mostly meant for displacementmaps.

What I´d want is to load a *.hdr image, render using it´s
linear float input, probably *see* the gammacorrected
input to correctly set the f-stop and have the renderregion
and OGLviews display things gammacorrected. Oh, my:-)

Now I´ll check the wiki again.

Cheers

tim





----- Original Message ----- 
From: "Luc-Eric Rousseau" <lucer(at)Softimage.COM>
To: <XSI(at)Softimage.COM>
Sent: Tuesday, April 04, 2006 6:56 PM
Subject: RE: (*.hdr) environment shader questions


> If you're using HDR, you can't enable the Image Clip effects.  The image clip 
> effects are all low-dynamic range and will clip the HDR values.  Why would you want 
> to use the 8-bit to 16-bit conversion?  An HDR file is floating point not 8-bit.
>
> That bit depth conversion effect is used in theory when you want to use an 8-bit 
> image for a displacement map, and you convert it to 16-bit before using correction 
> or blur on it, to get extra detail.  This is all in the manual.
>
> The display gamma stuff is all for viewing the images correctly in OpenGL, and it's 
> already offering the correct parameters and correct features.  You do not use any 
> gamma correction before sending the image to Mental Ray, but let mental ray load 
> the image directly without any preprocessing, and do any processing in the render 
> tree instead.  The Image Clip has gamma correction for OpenGL, and the render 
> region has its display gamma setting too.  This is all explained on the wiki.
>
> "Display Gamma Affects Rendering" is mostly for users who don't understand linear 
> floating point, or dont' want to use it (because it can indeed be a pain). It's 
> gamma correction implemented in the mental ray image shader itself, as if you had 
> added a gamma node in the render tree
>
> ------------------
> Luc-Eric Rousseau
> Team Leader, User Interface
> Softimage|XSI
>
>
> > -----Original Message-----
> > From:Tim Leydecker
> >
> > Hi folks,
> >
> > I have problems in understanding the behaviour
> > and settings when using an environment shader
> > together with a *.hdr file in XSI 5.01 (5.1different?).
> >
> > *Will the high dynamic range be used by default?
> >
> > *Why does the intensity change (in a rendering) when
> > you click "Adjust>enable effects", shouldn´t the intensity
> > stay as it  is until you actually modify an accompanied slider?
> >
> > *Is the conversion from 8>16 bit to be checked or not?
> >
> > *How do I block the environment shader from appearing
> > in the alpha channel?
> >
> > *I simply don´t get the behaviour of the "Display Gamma"
> > and "Display Gamma affects rendering" depending on wether
> > "Enable Effects" is a ctive or not.
> >
> > I *think* one would want to have linear input for
> > rendering and only the final result gamma corrected?
> > Or do I need to have gammacorrected input to get
> > reliable gammacorrect output without wasting details?
> >
> > *8-16 Bit per channel just interpolated values to fake
> > a higher dynamic range, doubling them or what does it?
> >
> > What I´d like to have:
> >
> > *Display Gamma for previewing the image according to the
> > monitor settings (e.g. 1 - 2,2). As you´ll probably know it
> > from hdrshop...
> >
> > *Exposure (f-stops) moved to the "enable effects" section.
> > *ColorCorrection not modifying anything unless you change
> > a sliderposition
> >
> > *"DisplayGamma affects rendering" renamed to something
> > that makes you understand the Gammacurve of the image
> > is either modified (>monitor) or maybe even ignored for
> > linear...
> >
> > *Add an Alpha (>blackhole)switch to the Intensity sliders
> >
> > *Move the Intensity sliders to the "Adjust" page.
> >
> >
> > Cheers
>
> ---
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