Hi Votch,
Looks like what I'd expect as the antialiasing is being done in float
space - so these are probably nice smooth values when looked over the
full range. But when clamped between 0->1 you're getting aliasing, but
cause you're not seeing the true values.
Cheers,
Alan.
On 7/6/07, Votch <megavotch(at)gmail.com> wrote:
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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