View Full Version : probably a stupid question

11 November 2008, 06:00 PM
I don't know anything about the layer passes and all in Max 9 and Vray. Here's what I'm doing. I have a scene split into two parts. The main part is a basic street scene, buildings etc. I'll render it out at a large format using Vray and GI and all that jazz.

Then I'll take my secondary scene, which is mostly just the street, for shadows, and a character, against green screen, matched lighting, GI and the whole same setup. Then I'll composite in Photoshop most likely.

Or, I may set up the first render as the background image and render the character on top of that. IF I do that, is there a way to optimize the background scene to have it look it's best?

I'm unsure of how to go about it really. I'll also be rendering occlusion passes for both. After my computer fried because of an improperly wired socket in the house, my sister replaced my computer, but it only has a gig of memory, and when I try to place my character in the main scene, the computer crashes as soon as it gets to the character, so I'm forced to do it this way. I'd much rather do it all at once, but it's not going to happen. At least not until I can afford the horrendously expensive DDR1 memory to boost it, or until I can score a decent computer. Never having had a decent computer, I've always had to do workarounds. So basically, I'm hoping someone can give me some ideas about the best way to do this.

11 November 2008, 11:59 PM
First of all: DO NOT RENDER your street for shadows, use parks, mansions, mountainscapes etc. instead.
Also, if you render your character against green screen, make sure you light the screen with 5K FLUORESCENT LIGHTS ONLY obviously talking severe HDRI radiosity spill into account.

If you want to make the background scene look its best, use 220volt sockets only. Computers wired with 220volts render the best scenes.


Sorry, I don't mean to be rude.

Your post was at first very hard to understand, until I read it a bit better.
If I understand correctly (greenscreen put me on the wrong track I guess) You are rendering a still image purely in 3d, and dont have enough memory to render the entire scene at once, is this correct?

Also, you are not familiar with the elusive 'alpha channel', I assume this because you want to use a green screen (which is normally only used when real video footage is used)

What you want to explore in this case is rendering your character with an alpha channel (which means transparancy where you need it, ie. not where the character is) and for your basic street geometry shadows the use of matte materials (in vray this is the material wrapper) look into those and you will find what you need.

Do not use green screen tricks, they do not offer the best results and restrict the use of colors.

in case of GI it might seem a better idea to look into optimizing the poly count on your character in order to render all at once.
BTW layer passes afaik do not help with this problem, they just seperate the lighting, shadows, occulsion, color, etc. passes but do not help compositing two different scenes together.

11 November 2008, 04:53 AM
Probably the best thing to do would be to read some pages on the Internet about "compositing."

When you see the word, passes, you know that it always means "breaking down a complex task (like a render) into component parts that will eventually be combined (composited) back together."

Digital renders don't have to use "a particular color" to distinguish between "what is subject and what is not." Instead, a fourth channel of information ... in addition to "Red," "Green," and "Blue," is used. This channel is called "Alpha," and it indicates transparency.

A typical example is... shooting a lot of action in front of a background from a camera that doesn't move. If the camera doesn't move, you need only one frame of "all that background." Then, each of the components of the action are shot ... with no background at all. (The "alpha" here is 1.0 for image areas, and 0.0 for background.)

The various pieces are "layered" using the alpha channel of each "strip."

11 November 2008, 09:37 AM
You may even output a mask for each single object if needed. This element would be called a matte.

11 November 2008, 03:02 PM
Thanks a million. My disability affects my memory rather badly, and sometimes I don't remember simple things everyone else does. I had forgotten all about alpha channels. Doh!

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