btw, what does that mean?
> I checked your article in the wiki (and the spam added/removed:-),
------------------
Luc-Eric Rousseau
Team Leader, User Interface
Softimage|XSI
> -----Original Message-----
> From: owner-xsi(at)Softimage.COM
> [mailto:owner-xsi(at)Softimage.COM]On Behalf
> Of Luc-Eric Rousseau
> Posted At: Wednesday, April 05, 2006 12:35 PM
> Posted To: xsi
> Conversation: (*.hdr) environment shader questions
> Subject: RE: (*.hdr) environment shader questions
>
>
> I think you may have misunderstood the gamma correction bit.
> Of perhaps you did understand it, I'm not sure anymore.
>
> In XSI, there are settings for Exposure and Display Gamma for
> HDR and OpenEXR images. This is for OpenGL and other preview.
>
> You're not suposed to use the Image Clips Effects when you
> work with HDR or OpenEXR image.
> If you Enable them, you will get the gamma corrected image
> sent to mental ray and that's the wrong result, because the
> gamma correction is implemented in the image source loader.
> (It's also terrribly memory intensive as images buffers are
> copied over the Mental Ray.) So don't enable the image clip
> effects with HDR...
>
> With regards to running HSV correction on a 'normalized'
> version of HDR images, that doesn't work. It would only work
> reasonably if all the color channels in the image had the
> same scale and the image is pretty uniform, but then it
> wouldn't be a useful HDR image. If there are large
> differences between red, green and blue channels, you can't
> really say what's really "red", "green" or "blue" because it
> depends of where you're looking and what's the exposure.
>
> If Maya does have a shader that does HSV correction on HDR
> images, and uses a min and max value, it probably doesn't
> normalize the entier image, but rather apply the LUT on a
> region of values and leaves the other values outside of it
> untouched, which is the proper thing to do.
>
> If it was just up to me we wouldn't have image clip fx.., at
> least for color correction I mean why would have color tools
> there, then other kinds of tools in the RenderTree. A shader
> to do this in the RenderTree is totally reasonable, whereas
> I'm less keen on adding more feature creep to the Image Clip PPG
>
> ------------------
> Luc-Eric Rousseau
> Team Leader, User Interface
> Softimage|XSI
>
>
> > -----Original Message-----
> > From: owner-xsi(at)Softimage.COM
> > [mailto:owner-xsi(at)Softimage.COM]On Behalf
> > Of Tim Leydecker
> > Posted At: Wednesday, April 05, 2006 10:28 AM
> > Posted To: xsi
> > Conversation: (*.hdr) environment shader questions
> > Subject: Re: (*.hdr) environment shader questions
> >
> >
> > Hi Luc-Eric,
> >
> > I checked your article in the wiki (and the spam added/removed:-),
> > of course helps a lot in getting an idea about linear colorspace,
> > gammacorrection and image interpretation rules neccessary.
> >
> > DonÂt want to criticise any of that. ItÂs a great article.
> >
> > WhatÂs puzzled me is the Clipping to 8bit the moment you enable
> > effects on an image (that has >8 bitdepth), if I understand you
> > correct, the image is then gammacorrected (according to prefs) and
> > passed to mR, resulting in a completely different
> rendering/backround.
> > As the gammacorrection doesnÂt happen for the native HDR file but
> > only for the clipped 8bit converted file.
> >
> > I *would* have instead expected an *.hr with the Exposure=0
> > and the 8bit converted image to *look* identical, e.g. the clipping
> > being based on the exposure set in the slider for example.
> >
> > Regarding the OGL display allways requiring a gammacorrection
> > for floating point images, no critique here either. ItÂs logic.
> >
> > Yet, in terms fo working with fp images, IÂd think still think all
> > colorconcepts are still adaptable if you normalize all images
> > (not to be confused with a gammacorrection) to the 0-1 range.
> > Which is what you can do with Maya, the min input is declared
> > black, the max is pure white, for color operations. YouÂd need the
> > displaygamma to correctly set the exposurelevel if you want a
> > lowkey or highkey image (e.g. something without absolute black)
> > out of that. ItÂs true, you canÂt load such an image without having
> > an idea what it contains, the normalization always makes it a
> > *perfect, full range* image by default. IÂd need to check the specs
> > of the *.exr format, afaik they attach a certain exposure to
> > the monitor
> > displaygamma via the header, but I never working/fiddled with
> > *.exr yet.
> >
> > I *think* itÂs like for exposure=0, thatÂs why I was puzzled
> > initially.
> > Maybe IÂm wrong and there is not such thing in HDR/*.exr files.
> >
> > Cheers
> >
> > tim
> >
>
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