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View Full Version : image quality loss when applied as IBL


transmoderata
07-03-2010, 10:59 PM
I'm using this (http://i456.photobucket.com/albums/qq284/pellaamarilla/mayahelp0.gif) star field image as an IBL (that's only part of the image.) When I render, it looks like this (http://i456.photobucket.com/albums/qq284/pellaamarilla/mayahelp-1.gif). As you'll notice, the rendered image is much more blurry and less crisp; the stars completely lose their definition. Is there a way around this? I really want the star field to look spectacular, and this just isn't cutting it.

jschieck
07-03-2010, 11:37 PM
u could try applying it as a texture instead and turn off filtering, see if that helps at all. or make a big sphere and just use that (i'm assuming your just using it for a bg)

transmoderata
07-04-2010, 05:54 AM
Using it as a texture and turning off the filter had a minimal effect, still nothing close to what I need. That's beside the fact that I need to use IBL for reasons discussed in this (http://forums.cgsociety.org/showthread.php?f=7&t=897080) thread.

transmoderata
07-04-2010, 09:57 AM
I should mention that I'm rendering in mental ray. I've messed with the multi-pixel filtering settings and gotten a noticeable improvement, but it's still this:

http://i456.photobucket.com/albums/qq284/pellaamarilla/mayahelp1.png
(portion of original image)

vs this:

http://i456.photobucket.com/albums/qq284/pellaamarilla/mayahelp2.png
(rendered)

I need the crispness of the former to be retained in the render. It also sees like the contrast in the rendered image is lower, making it look more monotonous. I've tried using .tif format, and made sure the image dimensions are 2^x.

transmoderata
07-05-2010, 09:07 AM
I just found out that maya software renders the image as a texture perfectly. But I need to use mental ray...

chafouin
07-05-2010, 10:03 AM
Maybe it comes from the multi-pixel filtering you're using, in the render globals? Some of them are crisp, some of them are smooth, and you can modify them with the filter size just below. But using slow filtering like Lanczos will affect your render time.

transmoderata
07-05-2010, 06:20 PM
Maybe it comes from the multi-pixel filtering you're using, in the render globals? Some of them are crisp, some of them are smooth, and you can modify them with the filter size just below. But using slow filtering like Lanczos will affect your render time.

I've messed with the multi-pixel filtering settings and gotten a noticeable improvement, but it's still this:

http://i456.photobucket.com/albums/qq284/pellaamarilla/mayahelp1.png
(portion of original image)

vs this:

http://i456.photobucket.com/albums/qq284/pellaamarilla/mayahelp2.png
(rendered)

So, to repeat myself, I've messed with it. Quite extensively. I've tried Box, 1, 1, which (if I understand correctly) is the equivalent of no filtering. And I've tried very small filter sizes too, down to .25, .25. If you have a specific suggestion, I'd love to hear it.

After searching more on this problem, it's starting to seem like this is a problem with no solution as long as I'm using mental ray.

chafouin
07-05-2010, 10:46 PM
Oh sorry, I read too fast, I thought you just tried the texture filtering.

Could you send me your scene? I have a lot of things I don't understand in your problem.

Here are some of them:
Which maya software setting do you use to get it works perfectly? I guess it's the default one without any anti aliasing and filtering.
How do you render an IBL with maya software since IBL is a mental ray node? :curious:
How is your texture mapped to the IBL? You just gave a part of the image that needs a cylindrincal mapping. Unfortunately the IBL node only has spherical and angular, so I can't test it on an IBL.
Is your texture streched when applied to the IBL?
Is your texture big enough for the resolution you want to render?

Since your texture is "1 pixel is a star", except if your texture size is exactly the render resolution, it will be obviouly filtered and blurred, or if not filtered, pixelated when scaled up or missing stars when scaled down.
Edit: I did a try with using your texture as an image plane, I did managed to have good results with a fixed sampling to 1 and Lanczos 4-4.

I'm trying to narrow down all the possibilities...

axiomatic
07-06-2010, 04:58 AM
Do you absolutely need this to be in the same pass?

I've done star fields in the BG before and simply rendered main passes with IBL as refl/FG contribution etc, but with Primary Visibility turned Off, then just rendered another pass for background stars in software at 0.5s per frame.

Apart from that I'd imagine that what you're seeing is stretching of the texture ... you're applying something that's 'flat' to an IBL sphere defaulting to Spherical mapping ... so the middle pixels of the texture are stretched wider than the top/bottom pixels. Try increasing the original image to 4k and see how it goes. Should turn out a lot crisper.

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07-06-2010, 04:58 AM
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