Re: (*.hdr) environment shader questions

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

Hi Luc-Eric,

I donÂt want to be offensive or anything when I
still find it more failsafe to do image operations
and manipulations without clipping nowadays.

> With an HDR or EXR images, the pixel buffer
> given to mental ray when the effects are on is an
> 8-bit image gamma corrected and meant for
> OpenGL previewing, not a floating point HDR image.

At least this gammacorrection is therfore wrong, imho.
Only the output from mR and the OGL display should
be gammacorrected but not clipped beforehead.

I really donÂt want to stirr any mess or resentiments.

ItÂs just that everything and everybody slowly transfers
over to lossless higher bitdepths for their work, even games
make use of HDR rendering (mostly blooming highlights),
it would be great to have XSI do itÂs operations accordingly.

E.g. conceptually adapt working in an unclipped colorspace
that may even have room for Ultra-HDR or 128bitfull*.exr
or whatever the next killerformat will be called.

I donÂt want to insist on the NTSC luminance concept either,
itÂs been an example to illustrate things. HSV imho still works,
itÂs just more V(alues). Same for H and S. Greyscale HDRÂs
are actually great for setting up materials well lit but colorproof.

Cheers

tim












----- Original Message ----- 
From: "Luc-Eric Rousseau" <lucer(at)Softimage.COM>
To: <XSI(at)Softimage.COM>
Sent: Tuesday, April 04, 2006 8:42 PM
Subject: RE: (*.hdr) environment shader questions


> We don't really care about the color correction effect in the Image Clip Fx for 
> HDR.  It's a classic correction effect that converts RGB pixels to HSV and back, 
> which necessarily means clipping HDR values.  If you want to work with HDR images, 
> you have to use nodes in the render tree such as multiply.  The render tree is the 
> place to work in floating point.  Hue and saturation do not necessarily make sense 
> with HDR images.  Luminance is also a clamped color space concept, in fact here or 
> in photoshop and other products, it's an operation slanted for NTSC luminance.  All 
> three Hue, saturation, and luminance are all concepts that exist for user interface 
> in a low dynamic range world.
>
> > -----Original Message-----
> > From: Tim Leydecker
> >
> > O.k. Thomas,
> >
> > I missed that bit in Luc-EricÂs previous post:
> >
> > >>If you're using HDR, you can't enable the Image Clip effects
> >
> > I didnÂt realize Colorcorrection as implemented in an
> > Image>Adjust section is 8(16)bit only. Makes sense,
> > as the FXtree is *only* 16bit as well.
> >
> > I had asumed that the input, regardless of itÂs bitdepth,
> > would be normalized to the 0-1 range only for the
> > sliders, e.g. 0.1 would be a compareable lumavalue
> > in any 8,16,32bit b/w gradient but obviously the higher
> > the bitdepth, the more steps available for rendering and
> > the smoother the output.
> >
> > Thanks for making me aware of the clipping to 8/16bit.
> >
> > IÂll log a featurerequest to have this changed, e.g. have
> > CC-Operations work without prior clipping in a later
> > version of XSI. I guess they are looking into this allready, tho.
> >
> > Cheers
> >
> > tim
>
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