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manuqc
01-20-2012, 07:49 PM
Hello,

I am currently trying to practice some lighting and decided to work on an old scene.

The scene lighting is using Sibl plugin (sun&sky) also a portal light and a mia photometric (40w spotlight)

Although I am having issues of some artifacts and also antialiasing. My metal materials have glossiness samples set to 32. And I am wondering if this is too low as the sun is hitting strong on those surfaces. I will like to get rid of the artifacts and antialiasing. So hopefully you can help me out.

Here is my current render:
http://dl.dropbox.com/u/4138955/drop3d/3dtests/render-test-artifacts.jpg
and you can see the artifacts in orange.

Also here is a very quick retouch in PS, showing the mood I will like to achieve:

http://dl.dropbox.com/u/4138955/drop3d/3dtests/mood-test.jpg

here are my render settings for that render:
http://dl.dropbox.com/u/4138955/drop3d/difference.jpg

And here you can see the scene lights:

http://dl.dropbox.com/u/4138955/drop3d/3dtests/lighting-setup.jpg

So my questions would be:

1) how can I get rid of those lighting artifacts to get a clean render. (this is intended to be a still frame, which I am thinking to transform into a moving matte painting.

2) In the render picture it shows, trace deph inside "indirect illumination" tab and also the "render" tab what is the difference between both? Is one more important than the other?

3) When I use the Sibl plugin I noticed that the images rendered look washed out until I disable the camera lens "Sibl lens node" that creates with the lighting rig. I have my gamma settings set to input/output (2.2) And I am not working with a comp package for this one. Only photoshop. Can someone please explain me this. I am not sure if I should leave the "sibl lens" and adjust gamma in PS or simply remove it.

4) Lastly I realized that then I add a portal light in front of the scene (in front of the Mr Sun) it does render as a "black square" does someone have any idea why is this?

I thank you in advanced for your help.

Hopefully I can get this issues clarified and keep working.

Regads.


-Manu

kanooshka
01-21-2012, 01:06 AM
Hi manuqc. You're off to a good start!

1. Getting rid of noise is all about samples. It could be samples in the materials' reflection, or from the a light source. It's important to isolate where the issue comes from first. If you disable blurry reflections and still see noise then you need to increase your lights' samples. If you have to you can solo your lights to determine which is creating the problem. If the issue ends up being with the material then you can try increasing the reflection samples or possibly decrease the amount of reflection blur. Depending on the type of material, you may also be able to use interpolation in the material's settings.

2. Trace depth under the render settings applies to direct lights and reflections. Under indirect it only applies to how many reflections/refractions the indirect illumination is visible in.

3. If you're using HDR images you do not want to apply any gamma correction to them because they're already in linear space. The rule is non-HDR textures need gamma correction of .454, HDR textures get no gamma correction, and after rendering a gamma correction of 2.2 is applied. I haven't had any issues applying the 2.2 gamma correction in the render package via a lens shader but if you're using 16 or 32 bit image format I've had some issues with PS interpreting it correctly.

4. All I can think of is that you may have to disable the portal lights visibilty, but I'm not sure.

Hope some of this helps!

-Dan

manuqc
01-21-2012, 01:24 AM
Hello Dan!

Thanks for popping in! ok good point about the lights samples, I havent change that.
So thats something I'll try playing around.
Also for the material samples. As you say I am better off isolating the problem per material&light to see the root of it.

As for the hdr. As you say its already a linear image so it does not need a gamma correction on input. I usually set my scene globals to bitmap input 2.2, and apply a gama&gain shader utility to input .hdrs at 1.0 gamma. (Using real pixels 32 bit)
Question here, why I am given the "option" to choose 16bits as well (besides 32 on input), shouldnt hdrs work always at 32? I am just curious, I choose 32 bit anyways.

And as I am working with photoshop only I am outputing at gamma 2.2 and not linear.

Well I guess Sibl wants me to output linear thats why it adds the lens node that washes out the image, so by removing it looks ok. (hope I am not wrong)

I'll do some tests regarding the other points on the weekend and post some updates as soon as possible.

Thanks again for your time.

-Manu

manuqc
01-22-2012, 05:31 AM
Ok So I went through and did many tests, activating and deactivating lights, turning final gather on and off... changing anti aliasing type and quality...but the lighting artifact was still there and I wasnt sure how to remove it. Finally I tried turning "Mr exposure" off, and bang! problem fixed... but then I had not an artifacts issue but still a missing exposure render.

So then I turned exposure on and clicked on "process background and environment maps"
and things sort of seem to start working better. Now I am not really sure if I should use this feature? I guess something like exposure and processing hdr maps is something that should be done in comp to start of, but looks like its fixing the problem for a still render.

Here are some tests I did:
http://dl.dropbox.com/u/4138955/drop3d/example-lighting-processbk.JPG

I am having another issue regarding sibl and gamma correction. As I said on my first post the Sibl plugin from hdr labs generated a light rig that adds a "Sibl lens" shader to my render output, this shader is a gamma & gain shader set at 2.2 but I have the impression that my renders when using this default setup look washed out!

I am confused on why having an extra "gamma&gain" shader on my lens output if my global render setup is already at "output gamma 2.2"

So I tried simply removing this shader from my output and now it does not look washed out.

here is an example:

http://dl.dropbox.com/u/4138955/drop3d/example-lighting-sibl.JPG

Hope I am not being too confusing!

Ok so to be more specific I'll post some questions hoping some of you can help me.

1) Do you recommend using "process background and environment maps" feature in the exposure setup? (those this exists in maya?) If not why. Is there a workaround?

2) Regarding exposure. I am still a bit confused on how to handle this. Maybe not precisely for this image (as it'll be a still render tweaked in PS for matte painting) but for a regular 3D/compositing workflow.

What I mean is, how to handle exposure between cg and comp dpts. I did another thread some days ago and from what I can recall I was suggested.

a)to bake exposure into the lighting. How do I do this?

b)to use a comp package handle exposure. Ok seems logic, but then do I even have to bother using Mr. exposure control at all...? Lets say I do some test renders using it and I like the exposure settings, is there a quick/precise way to pass that to a comp package.

c) In the case I dont use exposure in my 3d package at all and only in comp. How can I test prove exposure, is the comp dept going to apply a master LUT for every test I'll do?


3) Regarding my last example on Sibl plugin, what'll be the adequate workflow? not sure about removing that lens shader... but I like better the result without.


Hope I am not asking too many questions! but I really appreciate you guys input. I have the impression that I learn the most from experienced people like you.

Thanks,

-Manu


Ps: you can right click and copy image location to see the images real size on the browser.

manuqc
01-28-2012, 08:29 PM
Hi There,

I wanted to bump this thread, hoping someone wants to share some thoughts about my last questions, thanks for your time.

-Manuel

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