Essential Blender- P26 pps

Figure RCD.33: Render Layer settings for the foreground. Figure RCD.34: Render Layer settings for the background. Notice that the bottom set of Layer buttons for the "1 Render Layer" layer only includes objects from scene Layers 1 and 11. The Layer buttons for the "Background" layer include objects from scene Layer 2. Looking at the node network, a new Render Layer node has been created with Add->Input- >Render Layers, and set to use the "Background" render layer at the bottom of the panel. As you will only be darkening and blurring this layer, you can stick with the default "Combined" pass. Figure RCD.35: The "Background" Render Layer node. Immediately after the "Background" Render Layer, we have added an RGB Curves node to darken and reduce the contrast of the render. Contrast can be reduced by performing the opposite of the "S Curve" — darkening the light areas and brightening the shadows. Before putting both layers together, though, you can use an old trick to help bring out the foreground objects. Quick and Dirty Depth of Field A simple blur applied to the background makes it look as though the camera lens is focused on the gauge. Figure RCD.36: The Blur node for the background. A Gaussian blur has been applied with X and Y settings of 5. We have used the Gamma button to emphasize the bright parts of the image, ensuring that the out-of-focus dials remain visible. Also, as we're pretending that the background is blurred due to camera focus, it might be worth it to use the Bokeh option. Figure RCD.37: The blurred, darkened background layer. The combination of the steam gauge with the background can be accomplished, once again, with the Mix node. This time, however, you will use the default Mix mode. How can you get the node to not blend the entire area of the images together, though? As you've already learned, adjusting the Factor affects how much of the image from the lower input socket is composited over the other. In addition to just being a number, though, the Factor setting can also use an image as its input. By connecting the Alpha pass from the original Render Layers node, portions of the image that were completely opaque (the gauge itself) receive a Factor setting of 1.0, while the non-rendered areas receive a Factor of 0.0. The result is that the Alpha pass is used as a mask for the Mix node. Figure RCD.37.1: The Alpha Channel from Render Layer 1. Figure RCD.38: Mixing the background with the rendered element. Figure RCD.39: The rendered, composited image with background. Before you finish, you'll look at one more excellent use of the Compositor, one that's suited to animation but that can also enhance single-frame renders. Vector-Based Motion Blur Load the file "CompositeStage7.blend" and render to fill the passes. Figure RCD.40: The node network for compositing the spinning pointer. With this file, you will produce the animation. However, as the only thing that moves is the pointer on the gauge's face, it would be a waste of time to render the entire image once for each frame. The animation for this piece is 250 frames long, and each frame takes, on the computer used for this discussion, almost a minute to render. That is almost four hours of render time. If you use a single minute-long render to produce a background, then render only the pointer as it spins, you can reduce the per-frame render time to around two seconds, saving nearly three hours and fifty minutes of render time! In this new file, you will see that only three objects exist: the pointer and the main body and face of the gauge. You will only use the render of the pointer when you make the final composite, but the shape of the gauge itself will be useful too. When producing an effect like this, you will need to have already rendered the rest of the image, without the animated portions, to use as a background. We have already done that in the example file, bringing the image into the Compositor with an Image node found in Add->Input->Image. Also, the only 3D objects left in the file are the pointer itself, the main gauge body and face, and the lamps. If you had wanted, you could have simply moved the extra objects to a disabled layer. Blender has two methods of producing motion Blur. The older method, available with the "MBLUR" toggle in the Render buttons, relied on rendering an entire scene several times on fractional frame numbers, then combining the results. Of course, this came at the cost of having to render your whole scene up to sixteen times per frame. Vector-based Motion Blur, on the other hand, uses the Compositor to examine how the objects in a scene are moving, then builds a new image with moving objects smeared along their trajectories and blended into the scene. Figure RCD.41: The Vector Blur node. Vector Blur is found under Add->Filter->Vector Blur. To make it work, you will need to have some sort of image to blur (either a Combined pass or a composited image), and the Z and Vec passes enabled in the Render Layers tab of the Render buttons. In this example, all three input sockets connect directly to their output counterparts on the "1 Render Layer" node.