Finishing a 3D Render – Passes, Compositing, and Touch Ups

A Post Production Checklist for CG Artists - Part 1

You've spent hours upon hours modeling a scene. You've UV'd every asset, your textures turned out great, you're happy with the scene's lighting. You click render and wait — and wait — and wait. Finally, the render finishes. Finally, you get to open your handiwork and view the finished image.

But you bring up the file, and the work disappoints. “Where did I go wrong?” you ask yourself. Although it's impossible for us to tell you what other mistakes you might have made along the way, we can point out at least one misstep:

Your Raw Render Should Never Be Your Final Image

It doesn't matter how much time you spend tweaking your lighting, composition, and render settings — there is always, always, always something you can do in post-production to make your image better. Just as post-work in Photoshop is a crucial part of a digital photographer's workflow, it should also be part of yours. In fact, in many ways, the post-processing workflow for CG artists is quite similar to that of a photographer's.

Here are some of the techniques you can use to turn your base render into a finished piece.

Render Additional Passes:

3D image

Aeriform / Getty Images

Does your scene feel like it lacks an overall sense of depth or weight? Adding a few additional render passes to your workflow can help spice up your raw render very easily.

If your objects and environments don't feel as if they're occupying a unified space, rendering out an ambient occlusion pass and compositing it on top of your render can work wonders. Ambient occlusion creates what artists call “contact shadows,” darkening the tight cracks and crevices where any two objects come together or interact. Ambient occlusion can add weight to your scene, make your details pop, and make it feel as if your models are actually occupying the same three-dimensional space.

Aside from ambient occlusion: Rendering out a Z-depth pass gives you the opportunity to add depth of field effects in Photoshop or Nuke, and rendering a color map (which assigns a random color mask to every object in your scene) gives you more masking control in post.

You can take your render passes even further if you feel the need, rendering out separate passes for shadows, reflections, and caustics as you see fit. Take some time to read up and experiment with passes. It can open the door to a lot of possibilities.

Touch It Up

Don't be afraid to bust out the old Wacom and use Photoshop to paint, overlay textures, and add effects to help bring your render to its final state.

There are certain things that are either very difficult or very time consuming to pull off in 3D — smoke, fire, hair, volumetric effects, etc. If you want these things in your image but don't know how to how to create them in your 3D package, simply add them in post!

I know at least one or two artists whose final step in post-processing is to go over an image with a very fine “particle” brush in Photoshop to add a very subtle layer of airborne dust. It's something that takes very little time to complete, but can go a long way toward bringing an image to life, and it would have been far, far harder to achieve in a 3D package.

You don't have to do exactly that, but try to figure out how you can use Photoshop to your advantage! Drop in textures or lens flares, paint out render artifacts, add some drama through motion blur. Analyze your image like a photographer would analyze a raw photograph, and ask yourself, “what is this image lacking, and what can I add without going back into my 3D package?”