The rendering consisted of just two passes: one for the car and the other one for the shadow on the floor, which was just a cylinder with a neutral gray material. For the car pass I just rendered everything, floor included, and then rendered out a mask of just the car by itself, so that I could later isolate it from the background. In order to get the mask, I deleted the floor and assigned a Lambert to the car model, with Incandescence set to white, and rendered that out (Fig.12).
I made the shadow pass by assigning a Use Background shader to the floor. This shader was used to "catch" the shadows below the car. The advantage of it is that it also "hides" the floor from the final render so that you only have the shadows to work with, which are stored in the alpha channel, so just make sure that when you save it you use a format that saves alpha channels, such as Targa or TIFF. Also, in order to just get the shadow and no car, I selected the car model and set its Primary Visibility to off. I could also have assigned a Lambert to the car model and set its Matte Opacity to Black Hole, which in turn would have cut the car's shape out of the shadow, but I decided that I wanted the entire shadow below the car because I was having issues with a thin white edge showing up between the shadow and the car when I did the compositing in Photoshop (Fig.13).
The rendering settings are shown in Fig.14. Final Gathering Accuracy was set to 600. It is important to notice that I changed the Multi-Pixel Filtering from Box to Mitchell, which resulted in nice, crisp edges.
Compositing was done in Photoshop. It was simple, just requiring the few passes I mentioned before plus a background I painted (Fig.15).
Of course, I did some color correction, and a bit of level correction, as you should do with any render you make! In Fig.15 you can see that I also did a few fixes, like adding a reflection on the headlight, which I thought would give it a nice touch. Also, I lightened the rim cap and the blinker on the front fender. All of these could have been corrected in Maya, but since this was a still image, it was quicker to make them in Photoshop - especially the headlight reflection, which would have required lots of testing in Maya to get it right. So yeah, I believe that most, if not all, of the professional renders you see around have a lot of Photoshop done to them. And it's not a bad thing at all: it's just a tool used to improve your renders!
The final renders are shown in Fig.16.
So, in conclusion, I learned a lot by working on a model from the first polygon in 3D to the last touch in Photoshop. Every stage was completely different from the one before. Modeling is all about observation and studying the subject. Texturing is about understanding the materials: what they are made of, how they reflect light, their properties, etc. Lighting requires lots of patience, because you'll be doing lots of test renders! And rendering and compositing are the last steps where you bring everything together to make it nice and shiny.
I hope you enjoyed this Making Of and feel free to email me if you have any questions or comments.
Fig: 16 - Final Render