Node Compositing
Node compositing can be difficult to understand, so take a look at the finished node tree in Figure 14.7. The nodes are numbered to help you understand the instructions that you’ll follow in this section. Remember, you need to press F12 and render a frame with the Render Layers set up so you can load them in the Node Editor: if they’re not rendered, you won’t see anything in that editor!
Figure 14.7 Here, the node tree is numbered so you can follow the instructions in this section. To see the full node tree with no numbers, go to the end of this section.
Now, let’s go through the step-by-step process of creating this node tree.
1. Start with a Render Layers and a Composite (output) node. Move the Composite nodes all the way to the right, as the output nodes should be at the end of the tree (the Composite node is number 10 in Figure 14.7). In the Render Layers node (which is an input node, as it takes the render of the scene and inserts it in the Node Editor), at the node’s bottom, there is a drop-down list from which you can select the Render Layer you want to show in that node: select the Floor Shadows Render Layer.
2. Create an RGB Curves Color node. Connect the Image output from the Floor Shadows Render Layer to the Image input in the RGB Curves node. The curves allow you to correct colors. Click the B button at the top of the RGB curves node to work with the Blue channel only. Pick the point at the lower-left corner of the curve and move it all the way up, so the curve is basically a horizontal line at the top. Create a Viewer node to see how the shadow has turned completely blue. Change the value with the Factor slider at the bottom of the RGB Curves node to decrease its effect on the image. When you have applied the factor’s effect to the footage, you can come back here and adjust the factor until you’re happy with the result.
Note
If you’re not familiar with Curves from image editing software, they can be tricky to understand. You can modify the master color of an image or each one of the RGB channels. The master will control brightness and contrast, while the RGB channels will define the amount of each color in the image and the colors’ contrast as well. Basically, when you click the curve, you add points to it and, by adjusting the curve, you can add or subtract color in that part of the RGB spectrum: left is dark and right is light. If you set the curve higher to the right, you’ll increase the color in the bright values. If you set it lower to the left, you’ll make the dark tones even darker.
3. Now it’s time to mix the real footage with the shadow, so you need to take the footage into the compositor. Press Shift + A and, from the Input nodes, create a Movie Clip node. This should automatically load the clip you have been working on in the Movie Clip Editor. Otherwise, select the clip you want from the list in the Movie Clip node.
4. Let’s mix the shadows over the footage. Press Shift + A and create a Mix node from the Color node type. Set the Mix mode to Multiply (the blending modes work the same as in any other image editing software, and Multiply places the dark areas of one image over another image, and makes the brighter areas transparent). Because the shadows have Alpha, you can click the little button to the right of the blending mode selector to enable the Alpha of the image on top.
The Mix node allows you to merge two images. Input the image you want on the background (the real footage) in the top Image input, and then place the image you want to be the foreground (the shadows) in the Image input at the bottom of the Mix node.
Play with the Mix node’s factor value as well as the RGB Curves you applied to the shadows until they look similar to those in the real footage.
5. Jim should join the party now, so create a new Render Layers node from the Input group or select the Floor Shadows, duplicate that node with Shift + D, and switch the Render Layer selector at the node’s bottom to display Jim’s layer instead of the floor shadows layer.
6. You could mix Jim with the background using another Mix node; instead, create an Alpha Over (which is usually more efficient and gives better results when you need to just overlap a solid image with Alpha in front of another image) from the Color nodes as well.
Again, the Mix node has two Image input noodles. Connect the shadows and footage Mix node to the first input, and connect Jim’s Render Layer to the second input. Jim should now be a part of the image that results.
7. Jim may already be a part of the image, but it doesn’t look like he belongs to the scene. This is because his lighting is different than the lighting of the real footage. Create a new RGB Curves node between Jim and the Alpha Over node so you can modify Jim’s lighting until it fits better with the background.
8. Finally, you can even add another RGB Curves node after the Alpha Over node that merges Jim with the rest of the scene; this way you can apply some color correction to the whole scene. You might want to make it less bluish and increase its brightness—make whatever modifications you want until you’re satisfied. The idea is that first you integrate Jim into the scene and then you fine-tune the details.
9. The Viewer node should be active all the time so you can see the effects of your efforts. Now, connect it to the node that is connected to the Composite node to preview exactly what is going to be in the final output.
10. Connect the final node of your composition to the Composite node so that when you click the Render button that will be the final image Blender outputs.
Warning
The Composite node is really important. While you won’t need it until you’re done with the compositing, you must have it there if you want the scene to be rendered when you have nodes enabled. You’ll get an error if you don’t have it or if you don’t connect any node to it.
Figure 14.8 shows what the node tree should look like at the end of the process.
