|No matter how detailed the model, how perfect the texture or brilliant the animation, one final step always remains: rendering. While many think of rendering in rather simple terms, it is rather commonplace in the world of CGI that rendering is only one step towards the final goal of finishing off a shot. At one time or another, you've probably taken a still into Photoshop for a bit of final tweaking; perhaps adjusting the levels a bit or sharpening the image for an extra bit of "pop". Some new users in the world of 3D are actually suprised when they learn how much work is done in studios on a render, between the time it leaves the 3D app and hits the screen. Seems like a lot of extra work, right? After all, if you can just do it all in 3D - why bother? The answer is quite simple. Many things are easier to do in post... not to mention that it can be a lot faster.
One of the key steps to post work is "multipass rendering". If you aren't familiar with the term, it's really a simple concept. Instead of rendering one image, you render the image in layers. For example, a layer for the color, another layer for the specular, another for reflection, etc. Next, all of these layers are taken into another application and assembled in the correct layer order, and finally adjusted layer-by-layer until the desired look is acheieved. It might sound like a lot to keep track of, but in reality it's a very simple process when you have the right tools.
Maxon's Cinema 4D has an extensive toolset when it comes to multipass. Nearly every component of an image can be split into a unique layer, including elements such as the lights in your scene - and even camera movements. Of course, we need an application to assemble all of these pieces - and with AfterEffects 5.5, Adobe has truly delivered C4D users an excellent solution. Cinema 4D and AfterEffects are a very powerful combination, and in this 3-part tutorial series I'll show you how to get started in the world of multipass. We'll begin with some simple color correction using basic elements. In Part 2, we'll move on to more advanced multipass using several image layers. And in Part 3, we'll go full speed into AfterEffects and see how much power you have when you combine these two applications.
Now, before we get started I'll make just a few quick points. First, these tutorials *require* Cinema 4D XL v7.303 and AfterEffects v5.5; earlier versions of these applications will not work (as they didn't contain key features we'll be using.) Don't forget to install Maxon's AE plugin into the AfterEffects plugin directory. Next: though these tutorials are basic in nature they do require you are familiar with both C4D and AfterEffects. You need to know how create objects and materials in C4D, as well as the basics of importing files, adjusting layer modes and applying filters in AfterEffects; if a part of this series seems completely foreign, have your manuals nearby to refer to. Be sure and download the example file for each tutorial as use it as you follow along. Each file contains pre-made scene elements to save you a bit of time. Finally, have fun! Ok, let's get to it.
Part One: Introduction to Multipass
Download the project file, either here or above in the green bar.
Open the C4D scenefile in the archive, called "MP_tutorial_1". The scene containins 3 cylinder primitives, a floor plane, a shadow-casting light, and an animated camera.
Though this scene is obviously not complex in nature, it contains all the elements we'll need to get started with multipass. The materials are nothing special... just a black color with a bit of specular. Move the timeslider around and you'll see the camera pan around the image. Now, go to the Object Manager and you'll notice I've applied a render tag to each cylinder object. Double-click the render tag on Cylinder 3 to open the tag properties:
The important bit we're interested it is at the very bottom: the section labeled "Add to Object Buffer". You'll see I've checked the first box, and input a value of "3". Now, what's an Object Buffer? It's very simple: an Object Buffer is rendered as an alpha channel containing ONLY alpha information related to the object it is applied to. Normally in 3D, an alpha channel takes the whole scene into account. This can be a bad thing when using things like Sky Objects or Background Plates, as those eliminate the scene-wide alpha channel. With Object Buffers, we can get back some crucial image data. Now, the "3" I've input here is just a number... think of it as the name of the alpha channel: "Alpha Channel #3". If you open the render tags on the other two cylinders, you'll see that each one has it's own Object Buffer number assignment. Cylinder 1 has been assigned #1, Cylinder 2 is Object Buffer #2, etc. (Note: the Object Buffer number only matches the cylinder number in order to help keep the tutorial easy to understand. You could just as easily use "27" instead of "3" if you needed to.)
Now that we've got the render tags covered, let's take a look at the rendering preferences.
Above, we see the "standard" rendering preferences in the Save tab. You're probably familiar with this if you've ever saved a render in C4D. Here, we choose the file name, the render format - but the key part we're interested in is checkbox labeled "AfterEffects Project File". This is turned on, and by clicking the Save... button I've also designated a saving path for the AFX project file. Don't worry, this will make sense in a moment. At the top of the dialog, I've chose a Quicktime movie as the destination format. Now, this is important: the Save dialog ONLY products a FLAT image. "But thorn, you said something about multiple layers!" Yes, yes...hang on ;).
Now, in the render prefs click on the Multi-pass tab.
Things are starting to get more interesting. You'll see I have three Object Buffer channels set up for mutipass rendering. Did these appear automatically when the render tags were assigned? No, they didn't. In the top-right corner of the dialog next to the Channels: label you see a pulldown menu; use that menu to add various image layers (such as reflection, diffuse, or object buffers). For Part 1, we're only going to multipass render Object Buffers. One important thing to remember is to turn ON the checkboxes labeled "Enable Multi-pass Rendering" and "Save Multi-pass Image". If you don't, you can guess what happens ;). Finally, you'll also note that I've assigned a different "save" name for the multipass files than was assigned for the quicktime movie. It's rather common I save these to a different file directory as well to keep things well organized... one you start rendering 12 passes in an animation, things can quickly get confusing if you don't make good use of file destinations.
On with the show...
Now, if you like you can render the animation before we proceed to the next step. OR... you can just use the rendered results found in the example archive. (Note: AFX may "lose" the footage once you import my example file due to directory issue. Just reload the footage in AFX and things will be happy!) Either way, it's time to move over to AfterEffects.
Once C4D has rendered this file, we'll find 3 basic "elements" which we'll use in AFX. First is the quicktime movie, second is a folder full of jpgs (the object buffer sequences), and finally a file called "MP_AFX.aec" (it's in the archive too). The first thing most people try (don't worry, I did too) is to double-click the .aec file ... and nothing happens. You'll probably get some type of "filetype unknown" error. This is because it's not an AFX project file - it's an AFX composition file, which we need to load IN to AFX.
So let's do just that. Launch AfterEffects 5.5. Create a new project. Now, in the Project Window we'll load the MP_AFX.aec file. Hey, look at that - there's all our layers!
The quicktime movie is there, along with an AFX composition. There's also a folder called "Special Passes" which contains the Object Buffer sequences for the 3 cylinders. Now, double-click the Composition to open it. The timeline will appear.
There are 3 layers in the timeline: cylinders.mov (the quicktime RGB image) along with a camera layer and a light layer. We aren't concerned with the camera/light in Tutorial Part 1, so just ignore those 2 layers. (Why did I leave them in the screenshots? Because that's how they'll import on your system, and if I deleted them you'd wonder why YOUR comp was different... hahha).
Ok, so how about those Special Passes? Why aren't they in the timeline? Well, consider it a convenience... sort of. Special Passes are layers which have no absolute purpose; they are used on a utility basis according to the demands of individual scenes. Therefore, we add them manually as needed to the AFX comp.
Our goal in this scene is to change the color of one of Cylinder 1. There's no particular reason we're changing the color... but once we've finished, you'll see that this can be accomplished much faster in AFX than perhaps to re-render the scene in C4D. (Imagine it was a 30-second animation... big difference, no?) This only takes a few simple steps. First, drag the Special Pass called "cyl_M_object_1_[000-029].jpg" (I'll refer to this as the SP layer) into the timeline. Next create a 320x240 Solid Layer in AFX, and give it a blue color. Arrange the layer order as shown:
Once the layer order is complete, there are a few parameters we'll change. First, change the timeline in AFX to Transfer Mode. Change the mode on the Solid layer to Add. Next, change the Matte type from None to Luma matte. Finally, change the opacity of the Solid layer to around 50%.
And voila. Cylinder 1 is now blue! Move the timeslider around... the camera will rotate around the scene, and Cylinder 1 will stay blue!
Try it on the other 2 cylinders... utilizing SP layers, try changing the color of the other 2 cylinder to red and green - and remember that you'll need a solid for each color change, as well as to "knock out" the solid via the SP layer.
So there we have it... a post effect in AfterEffects, using some multipass rendering in Cinema 4D. Of course this just barely scratches the surface.