Re: FloatingPoint Render Weirdness

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

There is a logged bug for Maya 8 (mental ray: version 3.5.1.2) where
either *.hdr or *.exr (I´ve forgotten which format) will show AA errors
on very bright pixels when rendering floating point, rendering the file useless.

We where able to work around this by using the temporary framebuffer
file instead (mR/Maya creates during rendering), opening it in imf_display.exe
and saving that out. This was for highrez stills, not sequences, e.g. manageable.

I can´t comment on a similar XSI workflow/approach but would likely look for
an alternative, native 32bit mR outputformat instead of saving to *.exr/*.hdr.
Then do the fileconversion later, from those "direct" buffer outputs.

Cheers

tim


----- Original Message ----- 
From: "Votch" <megavotch(at)gmail.com>
To: <xsi(at)Softimage.COM>
Sent: Friday, July 06, 2007 9:53 AM
Subject: FloatingPoint Render Weirdness


> I've ran into a little problem when rendering to floating point images in
> 6.01. I've talked to support and they are looking into the issue but I
> thought I'd run it by you all as well.
>
> It appears that XSI/MR doesn't evaluate antialising properly in floating
> point pixels when a floating point file format is selected for the output
> file type. However when rendering to an 8 or 16 bit format everything
> renders correctly. It's strange because there is a visual difference when
> rendering to float formats compared to files rendered clamped.
>
> I've attached a scene that demonstrates the problem. Just render out all 10
> frames of both passes. Then compare the frames in a compositor. Frame 1
> looks correct because most values are below 1. As the spot light intensity
> increases the aliasing gets worse in high contrast areas as soon as pixel
> values go above 1. On frame 10 you can really see the issue.
>
> Support recommended using the ToneMapping lens shader. It works great for
> squishing floating point data into a clamped file, but it's not ideal
> because rendered images are no longer linear.
>
> In MR the error shows up with any float file format. All Clamped formats
> look correct as well.
> I also ran tests using this same scene in 3Delight via Affogato without
> issue. I haven't tried MR in Maya or Max Yet.
>
> I first noticed this problem in creature renders using HDRI environment
> domes. The reflection and spec always looked aliased in EXR renders but
> normal in TGA renders. After a lot of investigating I've come to the above
> conclusion.
>
> Anybody encountered this before? Any Idea's...
>
> Votch Levi


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