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Compositing a Realistic 3D Background
Submitted by: Ian Hubert

This is not a modeling tutorial. It is a compositing tutorial. I'll tell a BIT about modeling, but not much. Cause that's not what this tut is about. However, I will tell you a BIT about the modeling.

This background was made for an online miniseries, called, "Spacemen Belong in the Future, Probably", in which our only goal is to make them good, but make them fast. This means that, whenever possible, I take shortcuts. The biggest (and most blatant) is that I reuse pieces. In the below image, I spent a few days modeling a hangar for a ship. This was the most time intensive process. Even THEN I cheated, reusing pipes and beams. In fact, I don't think there's a single piece in that room I didn't use at least 4 times, excluding the overall room body itself.

Once finishing the Hangar, I duplicated it 7 times, giving me a total of eight hangars. It's supposed to look like a "hole", of sorts, with the walls being made up of hangars, however, I didn't have to make the ENTIRE hole, since the point of view is from one of the hangars anyways, so you'd only see the other hangars on the opposite wall. Meaning, besides what you see in the image, there really isn't much there.

BUT! Even THEN I wouldn't have enough computer "umph" to render out (or just have exist on the computer at once) 16 separate hangars. MEANING, that I'd have to cheat again. I turned off everything but the in bay lights, and rendered that out. It ended up looking like this:

Cute. Now, the top of the image is supposed to be open, and you'll see the sky, but the cavern is supposed to look like it has some depth, so I needed another two levels of hangars. To do this, I just moved all 8 of the bays down, so that they'd line up with the bottom of where they previously used to be. I rendered that out, and, using the "screen" option in photoshop, combined them into one image.

So this is what those two images look like when put together, made just of just the interior lights. You'll notice I went through the trouble of changing small things in each bay, such as the amount the door is open, or the angle or ships inside. I didn't go all out, cause that would have taken too long. Heck yeah.

Now, this is all fine and good, but the scene is supposed to take place during the day, meaning that just having interior lights isn't gonna cut it. We need to see everything ELSE, too. To do this, I rendered out an ambient occlusion layer, that is, an image in which the light is coming from all directions, simulating ambient light (such as the sky, and light from the sky reflecting off the ground). I made it so that the light from above is brighter than below, cause hey, sky is generally brighter than ground. Because dirt doesn't glow.

Though that would be cool.

Then I moved all 8 bays down again, and rendered THAT out, then put them together, getting the below image.

NOW you can kinda see how this is supposed to look. And I dig it. To put this image together with the interior lights, I just lined up the "interior lights" layer with the ambient occlusion layer, and used the "screen" option to add the brightness of the interior lights to the ambient occlusion layer. The result is seen below.

The rest of the process is very similar to this, with adding lights, then screening them on. Next we needed a sun. To create the appropriate shadow, I created an object that would simulate the rest of the nonexistent hangar cavern. Then I set up an area light (A nifty thing from which light is emitted from a certain area, instead of an infinitely small point. For, as we know, the sun is not infinitely small, and that's why your shadow appears more blurry the further from the ground it is.


So this is the result (at, like, 1/8 scale or something). Just the sun layer. I had to also render out the same thing after moving the hangars down, but I'm not gonna show you that. cause it's boring.

AHH! Now THAT is lookin' nice! It has a good contrast to it. I like it. I had to tweak around the brightness and contrast of the "sun" layer, but it was well worth it.

Now THIS is where it gets fun. Have you ever seen how when someone is holding a white piece of paper on a sunny day, the sun can reflect off the paper and make their face really bright? Then when they move the paper away it gets dark? Or how when a ray of light can shine onto a brightly colored blanket or piece of paper, it can make a whole wall that color?

An awesome thing. Which we should duplicate. With all the sunlight hitting the floor of the hangar bays, you'd think that SOME of it would be reflected back up to the ceiling. To show this, I just set up a light beneath the hangars, turned off shadows (cause otherwise it couldn't shine through he floors, and shadows aren't that important for this anyway), and rendered it out.

Ahh! As you can see, the light is just illuminating the ceiling. I erased by hand everything that should have been hit by the "reflected floor light", such as light shining onto the ceilings of hangars in which no light is hitting the floor. When added....

Oh! Now THAT is looking very much more realistic. Compare it to the image above. Yeah. It looks good.

A few years back I took a bunch of digital pictures of a local cement factory. This Hangar cavern thing is supposed to be in the middle of a factory, so I decided I could easily use those image. It took some rotating and resizing to make it look right (I had to flip the image to match sun angles), but it worked.

Here's the finished "above ground" stuff, with a few more pieces from the factory stuck in there. I made the ones furthest in the background brighter, with less saturation, so it would look like they were blending in with the background due to kinda a hazy air.

Now, here's something new that I've never done before: little lights. I'll include lights in my scene when I render them, but as far as just slapping lights onto an already made image... I've never done that.

To do it, I found an image I took of a local strip mall. I increased the contrast, decreased the saturation, and was pleased. It ended up just showing the brightest parts of the image (signs, bulletin boards, neon sights, little lights). Using the clone tool, I copied, piece by piece, those lights over to a new layer in the background.

This is what that layer looks like just on its own. Very nice. Lots of little lights.

And THIS is what it looks like composited with everything else. Ahh. I love it. Gives everything a feeling of realism, and random detail. I dig it.

And here's that same image with a little gradient wash on it. Obviously, in the final movie, the image will use the correction for the scene, but as a standalone image, I like it. I've always loved yellow blue color schemes.

So yeah! Hope this was at least a little help, even if just with the basics.