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The concept of multipass rendering involves the idea that the images that CINEMA 4D produces can be broken down into layers and those layers can be recombined in a compositing program to produce the same image that you saw in CINEMA 4D. The advantage is that you can adjust those layers to control how the rendering looks without having to comeback to CINEMA 4D to re-render everything. I'm going to be rendering a very simple still image into Photoshop to introduce you to the concept of multipass rendering. And then in the next chapter we're going to talk about multipass rendering for motion graphics working with After Effects.
So in the scene I've got this fish that swim pass the Multipass Workflow type. We're going to be rendering out frame 50. There's a little bit of movement on the camera but we're going to render frame 50 for this purpose. And so the multipass rendering workflow starts in the render settings. So let's go to the render settings, Command+B or Ctrl+B on the keyboard, and here in the Render Settings we're going to start of by telling it how big and what frame. Now I'm going to leave it on 800x600 because this is going to be a still image and that's going to be fine for these purposes. I want to make sure that I always render frame 50, so I change it to Manual and change the From and To to 50, and I'll hit Enter.
So I've told it how big and what frame to render. Now I can go to the Save dialog. The interesting thing about multipass rendering is that for the saving you do not have to worry about this Save image. When I activate the Multi-Pass option over here on the left-hand side, I'm going to get a new Save window, so let's activate that, and look at that, I now have a new Save section here. If I turn Multi-Pass off it goes away, turn it back on again and there it is. This is the Save area that we're going to worry about for a multipass rendering. If we did have an Alpha Channel in our image we'd want to make sure that this was turned on but we're going to be saving the file from down here.
So let's click on the Save Image button and we're going to navigate to our Desktop to the exercise files, so Desktop > Exercise Files > rendering, and then in the C4D-Renders folder we're going to save it loose here and let's call it Multipass-still. We've told it where to save. Now for the Format we're going to render to Photoshop, so PSD is good. For the Bit Depth, because I don't have a lot of really strong gradients, I'm going to leave it at 8. That's going to give me a slightly better file size to work with.
When you're rendering your still images for Photoshop, Multi-Layer File is the preferred way to go. However, if you're going to be rendering After Effects you want to make sure that Multi-Layer File is always off. After Effects will not be able to read a sequence of Multi-Layer Files. And also because of rendering a still image to Photoshop, we don't have to worry about the Compositing Project File information down here. We can leave that twirled closed. So we told it how big and what frame, and we've told it where to put the file and what format to put it in. We've left off the most important step and that's the Multi-Pass settings. Turning on Multi-Pass is not enough. We have to tell it what Multi-Pass layers we want to render.
So let's go ahead and click on the word Multi- Pass and we're going to Add all Image Layers. Don't be scared by this super long list. I'm going to break it down for you just a second. When we add all image layers, we get another long list of stuff underneath Multi-Pass. Now some of these we're not going to need and the way we're going to tell that is by doing a test rendering and looking to see which rendered layers are blank. The better way to know is by doing an analysis of the textures that you have on your scene, and based on the textures and lights that you have in your scene, that will tell you what renders passes you'll need.
But we're going to do a test render now so you can see just what those settings do. So we've got the Render Settings set. Let's do a Save As before we move on any further. Let's go to the File menu and do a Save As, and let's navigate to our rendering folder. We will call this Multipass-still-image-WORKING. Now we're ready to render. So let's do a Shift+R on the keyboard. We could also click on the Render to Picture Viewer button here but let's do Shift+R, it's the same for Mac or PC. So now that we've rendered this, the file has been saved to the hard drive.
How do we know that we've done a Multi-Pass render? Well, the easiest way to do is to check your layers. Right over here on the right-hand side of the Picture Viewer is this panel, and the panel can display different types of information. Now if your panel isn't visible for some reason, you can click on this icon up here at the top to make it active. We're going to click on the Layer option and the Layer option shows us all of the layers that we have with our image. Let's raise this up a little bit so we can see what's going on here. If I click on each of these I can't actually see them until I turn on Single-Pass.
Right now it's showing us the result of all of these layers. If I turn on Single-Pass then it shows me the layer that I click on. The thing you'll notice as I click through each of these layers, they represent a different component of the final image. So Atmosphere is all of the undersea murkiness that we see and that's based on the environment object. Atmosphere (Multiply) is what this atmosphere object multiplies into to give it the color that you see in the final image. The Refraction is blank. We don't need the Refraction layer. The reason we don't need it and the reason it's blank is because I don't have any transparent objects in the scene.
The Refraction layer relates to transparency. There's no transparency so I don't need refractions. I know that I can turn that off in the render settings. As I click through each of these you'll notice that there's a blending mode here and these blending modes are very important. They determine how the image will finally behave when you go into Photoshop, and they're already set for us. You don't need to change them here. If you change them it's going to change the way your image behaves and you want to do that in Photoshop not here in the Picture Viewer. So these are really just to let you know how it's going to get saved out. Reflection relates to the reflective surfaces in the object and the type is the only thing that has reflection on it, so that's the only thing you see here.
Ambient Occlusion is a pass that I haven't turned on yet for this image but it would be sort here. So we can turn off this pass or activate Ambient Occlusion for the final rendered image but I think we'll just turn it off for now. We're also not losing Global Illumination or Caustics. Ambient relates to the illuminates channel of your materials. I have illuminate channel in one of the materials on my type and that's what you're seeing there. The Shadow pass relates to the shadows that are being cast for the lights in your scene. The Specular Highlight is all of the specular highlights that are on your object, and then the Diffuse is the base level of color.
So if I go and turn all of these off, and then go to Multi-Pass, I can now build up my image and you see that I have Diffuse, if I turn on Specular, and now suddenly I've got some Specular highlight. I can turn on my Shadows, I can turn on my Ambient, I can turn on my Caustics--that's blank so that does nothing. Same thing for Global Illumination and Ambient Occlusion. I can turn on my Reflections, I can turn on my Refraction--that does nothing so I'll leave it off. I can turn on Atmosphere Multiply and then Atmosphere, and you can see there is my full image.
It is the result of all of those layers. The beautiful thing is that I can take these layers into Photoshop and manipulate them. Let's go into Photoshop and see how this image stacks up. So here we are in Photoshop. Let's go to the File menu and go to Open, and I'll navigate to my rendering folder out here and let's go to the C4D-Renders, and there is our Multipass-still. Let's open that up and here's our rendered layers. The rendered layers are all here just like they were in the Picture Viewer. Let's say I don't like how reflective the type is. I can go to the Reflection channel and then either turn it off or even easier I can just dial it down in Opacity.
If I take the Opacity slider and bring it down by say 50% I'm cutting the amount of reflection on the type. Then normally if I wasn't using multipass rendering I'd have to go back to CINEMA 4D, go into each of the materials, dial down the Reflection value, and then re-render everything. That's the beauty of multipass rendering. It allows you to make changes to the image right here in the Compositing application without having to go back and re-render. One more example, let's say I wanted to have a slightly stronger shadow. I can go to the Shadow options and right now my shadow is at 100%, you can see that the blending mode is set to Multiply.
I can just duplicate this layer by hitting Command +J or Ctrl+J on the PC and you can see that my shadows got darker. Each time I do Command+J or Ctrl+J my shadows will get darker still. So I can easily darken up those shadows without having to go back to CINEMA 4D and changing the light intensity. So as you can see Multi-Pass workflow is really a strong way to work. It gives you tons of flexibility. There's a little bit more to set up on the front end but it makes the backend in the compositing application much, much easier.
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