Compositing question (Use Background issues?)

[Undead Fred]

Oh yeah, I meant to mention that if you check the alpha channel, you can see the shadows from the room. I was just wondering if there was a way I could just change a setting or two without having to re-render the first pass or something like that.

[T0BER]

hi,

What renderer are you using and what compositing program? Are you using a complex lighting set-up like GI or FG?

If you are doing a composite render why are you re-rendering the background again in a shadow pass? Shouldn't you simply turn off the objects in the background if the character doesnt cast a shadow on them? Otherwise you are effectively doubling your shadow concerntration.

In your 'Render Globals' in the 'Maya Software' tab under the Color/Compositing section turn off the 'Premultiply' check and leave it at 0.000. this will remove the transperency from the outer edges of the solid objects, which will remove that black outline when comping.

[Undead Fred]

Ahhh, very cool. I'll try that with the black outline problem.

Yeah, I'm just using a regular software render (regular light setup I put in, production quality render globals, but I'm using a render farm with Muster... although I'm pretty sure that part doesn't matter). To composite, I'm using AfterEffects.

I had been talking about the problem with some friends, and the render flags and stuff came up in the conversation, and one of them suggested rendering the room without any shadows, then use the shadows in the character pass. The reason why I didn't go with all cast shadows turned off in the character pass (I know the version shown here has too many shadows, but this was like an initial pass) was that the room itself and the rafters over the window glass would cast shadows on the table and certain characters in the room. The solution I think I may go with is re-render the first pass with receive shadows turned off on the floor and tables, then turn receive off on the rest of the room for the character pass. I guess I just wanted to see if there was some way to not have to re-render the first pass. I will try that Premultiply thing you were talking about, though. I think that'll help the second pass' composite, at least.

[T0BER]

Sounds like a good plan rendering all the shadows in the second pass - that should work fine, but I can't see why you are bothering, why not render the lot in one pass? Is there a memory issue or something?

If you are trying to show a potential employer that you know how to composite a character onto a background plate then you would be going about it the wrong way, you would need to be creating shadow objects and flaggin them.

All the best.

[Undead Fred]

Well, the reason why I had to do it in passes was that I was having some memory problems with the whole scene rendering with more than one character in it... the full scene had about 11 characters total, plus I had a slight reflection on the floor and a big, reflective window... I'm thinking I could probably do the first two passes at once, then do a reflection pass? I was separating it into three passes just to be safe... I had assumed the shot with the rest of the people in the room would bottom out the memory on these computers.

[Shayder]

It's always good to render in layers. I use this a lot and it saves you a ton of render time in the end if you have to re-do things. If the shadows are on a seperate layer then you can adjust them to what ever opacity you'd like in the comp program. Specular layer is good too. Diffuse as well. The big boys will actually do passes for seperate lights as well that way they can tweak as needed.

[Undead Fred]

Yeah, aside from needing to at least render PART of the animation in layers, I figured I'd at least learn how to separate it anyway. You know, future reference info.

[Undead Fred]

Oh yeah, one more quick question- is it a good idea to ALWAYS turn off premultiply, or just in the case of compositing the character over the first pass? I had started re-rendering my first pass with the floor and table shadows off, and with premultiply off I had noticed there was still some white areas by the window rafters... I assumed they wouldn't be an issue, but I wasn't sure if I should do anything else with the premultiply setting.

[vimal]

this is with reference to u'r first question, why don't u cast of shadow for all the BG surfaces that u had given usebackground shader in u'r second pass, so that it would avoid casting bg shadows again in u'r composite........

[T0BER]

I uncheck the premultiply only when rendering layers for compositing. I'm not sure what's happening with your background render with the light - I would have to see it. You should only be getting opaque pixels when there is no geometry in the background (or a background shaded object) as they should have their transperency controlled by the alpha channel.

[Undead Fred]

this is with reference to u'r first question, why don't u cast of shadow for all the BG surfaces that u had given usebackground shader in u'r second pass, so that it would avoid casting bg shadows again in u'r composite........
Well, the reason why I didn't turn off cast shadows is that there was a shadow coming over the tables from the room itself and the rafters over the window. Also, in the first shot of the animation, there will be a guy walking down the aisle with a tray, so he'll definitely be passing through shadow areas cast by the room.

I uncheck the premultiply only when rendering layers for compositing. I'm not sure what's happening with your background render with the light - I would have to see it. You should only be getting opaque pixels when there is no geometry in the background (or a background shaded object) as they should have their transperency controlled by the alpha channel.
Ah, okay. Not sure if the opaque pixels become a problem, I'll post examples. But yeah, they're only appearing over places where there is no geometry so far (like outside the window). It should be all right, though.

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