Essential Blender- P25

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Figure RCD.02: The node network for this composite. The Composite Node network for this exercise appears to be staggeringly complex. However, it can be broken down into four distinct portions, each one covered here in depth. There are a number of files that will help with this chapter, all found in the "examples" folder on the included CD. The first exercise will require you to create the node network from scratch, but later ones will use pre-made files for you to examine and play with. Let’s start with the file as delivered to you from the production department. Load “CompositeStage1.blend” and perform a test render (F12). If you find that the render takes longer than a couple of minutes, you may want to consider working with the renderer set to 50% size in the Render buttons.
Figure RCD.03: The file as provided. If you examine the scene, you will see that some of the materials use raytracing. A simple textured plane outside of the camera's view provides something for the dial's face to reflect. Creating the Source Renders, Scenes and Components to Composite Change the wide window at the top of the screen from a 3D view to a Node Editor. Switch to Composite Nodes with the face icon on the header, and make sure the Use Nodes button is enabled. The window on the left side of the screen shows the Render buttons. Both windows at the bottom have been set to UV/Image Editors for showing Preview and Composite result nodes. You'll be focusing on the main gauge for the majority of this discussion, so disable Layers 2 and 11 to hide the background and wall elements.
Figure RCD.03.a: Shift-LMB click on these two layer buttons.
Figure RCD.04: A good setup to begin compositing. When turning on Use Nodes for the first time, the default is to have a Render Layers node connected directly to a Composite node. However, you are not limited to a single render input. It is possible to set up different Render Layers, each with their own node input, pulling elements from various modeling layers and scenes which can then be dealt with separately in the Compositor. These controls are found in the Render Layers tab of the Render buttons, nested into the same panel as the Output tab.
Figure RCD.05: The Render Layers tab. Render Layers From this tab it is possible to control exactly what will be rendered, as well as what will be passed to the compositor for processing. In short, a Render Layer is a selection of scene layers that will be rendered in a single pass: a set of Layers that will be rendered together. Each Render Layer can have its own Input node, allowing you to perform different composite operations on different sets of objects from your scene, as you'll see later. Let's look at the controls on the Render Layers tab: Scene
Figure RCD.05.1: Scene layer buttons. This refers to the set of layer buttons at the top of the panel. These controls are a duplicate of the layer buttons found on the 3D view headers, and are included here as a convenience. As you will be indicating which layers should be included with which render input in this same tab, it is nice to be able to check the contents of layers without leaving the panel. Below this is the name and selector for the active Render Layer. Like other name popups, new Render Layers may be created by selecting Add New and may be removed by clicking the "X" to the right of the control. Layer
Figure RCD.05.2: Layer Layer buttons. Further down is the Layer control, which again shows the familiar layer selector. Unlike the one above, which controls what displays in the 3D view, this selector is the one that determines which scene layers will be included in this Render Layer. When a Render Layer is created, it defaults to including all scene layers. Why would you need separate access to so many scenes and layers? You could, for example, divide a scene between background and foreground objects, sending the background objects to the compositor in a different Render Layer for blurring. It’s also possible to have part of your project in a completely different Scene, allowing you to composite objects with completely different render settings.
Figure RCD.03: Figure RCD.06: A render composited from two scenes. The ocean scene used standard render settings, while the mine and buoy scene used the Edge settings. Render Process Image:Dummy.png RCD.05.3: Render process buttons. Below the Render Layer selector are toggles for which portions of the renderer to use. Blender treats different types of objects in different ways, and each of these can be enabled or disabled here. For example, if you were to turn off the Solid button, no objects with solid faces would be rendered, leaving only the background. The other buttons can be used to disable rendering of Halos, Edges, Transparent (zTra) objects and the Sky background or BackBuffer image, on a Render Layer by Render Layer basis. Just below the render process buttons are two text fields: Light and Mat. If the name of an object group is entered in the Light field, the Render Layer will use lamps from that group, ignoring any other lamps in the scene. A material name entered into the Mat field will cause all objects in the Render Layer to be rendered as though they were temporarily linked to that material. These fields are useful for doing test renders and special effects. For example, you might need to substitute a simplified lighting rig and material to test object placement without actually replacing lamps and materials throughout your entire scene. Render Passes Image:Dummy.png RCD.05.4: Render passes buttons. At the bottom of the Render Layers tab are the controls for render passes. As Blender renders an image, it performs a number of calculations that are combined to deliver the final color of the rendered pixel. Render Passes allow you access to each stage of these calculations individually from within the Compositor. For instance, you could separate the Diffuse, Specular, and shadow
calculations, and recombine them in the compositor. By adjusting the way they mix, you could make the shadow darker or blur and lighten the specular highlights. Using a work flow like this gives you the freedom to drastically improve and alter the look of the final output without re- rending, potentially saving enormous amounts of time. On new Render Layers, only two render passes are enabled: - Combined, which delivers the final RGB and alpha results; and - Z, the depth information of objects from the camera's viewpoint. Each pixel in a render has a Z value, which refers to the distance between the camera and the face that was rendered. If you look in the Node Editor, you will see that the Render Layers node has three outputs: RGB, Alpha and Z. These outputs correspond directly to the Render Pass settings. Enabling any of the other pass buttons adds additional outputs to the associated Render Layer node. The other twelve passes are: Vec: Provides vector motion data for the rendered geometry. Mostly useful for calculating fast, vector-based motion blur. Nor: Provides the Normal information from objects in the render layer. If looking at the output of this pass in a Viewer node, the strange colors are the visual encoding of the Normal. UV: The UV information from objects that have UV mapping. This pass makes it possible to replace the colors on objects that use UV mapped textures, without re-rendering or changing the materials directly. IndexOb: You can assign any object an index value in the Object buttons and use this to create selection masks. Col: Provides an un-shaded color pass, as though everything had been rendered with a Shadeless material. Diff: The diffuse shading of objects, including colors, but without shadows or specular highlighting. Spec: Specular shading. Shad: A pass representing shadowing information. This pass is Multiplied with others to get a final image, so non-shadowed areas appear in white, with shadowed areas being progressively darker. AO: The result of Ambient Occlusion, without any materials applied.
Refl: The reflection pass, if Ray is enabled on the Render panel and an object has a reflective material. Refr: Refraction, if Ray is enabled on the Render panel and an object uses ray refraction. Rad: A radiosity pass. Radiosity is another method of lighting that is not covered in this book. If you would like to see the actual outputs from any of these passes, it's as simple as connecting their output sockets to a viewer node and re-rendering. Of course, if you already rendered after the different passes were enabled, no re-render would be needed. Figure RCD.07, .08, .09, .10 The Col, Diff, Spec and Shad passes. Recombining Passes For the first part of this exercise you will recombine the Diffuse and Specular passes to make the brass of the gauge's body a little brighter and shinier. You can either follow the simple instructions to set this up yourself, or if you prefer, load up the completed stage for examination. The file "CompositeStage2.blend" can be found in the "examples" folder.
If you want the practice of building your own, here's what to do: In the Render Layers tab of the Render buttons, enable the Diff and Spec passes. Figure RCD.10.1: Enabling the Diff and Spec passes. Add a color Mix node (Add->Color->Mix), connecting the Render Layer node's Diff output socket to Mix's upper image input and the Spec output to the bottom image input. Create a View node with Add->Output->Viewer, and connect the output socket of the Mix node to the Viewer node. If something was already connected to the Viewer node, that connection will automatically be replaced by the new one you make. NOTE: The nodes systems doesn’t like loops or ambiguity, and will frequently delete connections when you replace them with others, or warn you of problems should they occur. The Mix Node The Mix node is one of the most frequently used and important nodes in the compositing system. It defines how color passes or images from two separate inputs will be blended into a single output.
Figure RCD.11: The available mixing methods. A list of available mixing methods can be viewed by clicking the popup selector. In this case, choose Screen. Screen brightens an entire image, based on the image being mixed into it. Light areas brighten more, with white turning the other image white. Dark areas brighten less, with black leaving the image unaffected.
Figure RCD.09: The Specular pass. The specular pass in the example is mostly black with some lighter areas, so it won't brighten the other image much. We would like you to enhance the specularity, though, so you need a way to increase the brightness of the Spec pass. It could be run through an RGB Curves node and adjusted, but there is an easier way. The Fac (Factor) spinner on the Mix node controls the strength of the bottom image in the mix. Values of 0 through 1 represent 0 to 100%. The mix factor can go as high as 5, though, meaning that you can mix the Spec pass at 500% of its actual intensity. Set the Fac spinner on the Mix node to 4.77.
Figure RCD.14: The current node network. Figure RCD.12, .13 Increased specularity following the Screen Mix node. As you adjust the mixing Factor, the Viewer node updates without having to re-render. The brass gauge now looks a lot shinier, but could still be better. To do that, you'll apply a common post-process effect: bloom.
Bloom/Glow Real highlights, such a specular reflection, tend to behave differently than mathematically calculated highlights in a 3D package. Light intensity in the real world can cover a huge range that our eyes find difficult to view. As a result, very strong highlights can cause our eyes to actually overload in certain places, perceiving this dramatic contrast between light and dark as a kind of glow. Adding this subtle effect can make a render look more authentic and is a simple way of adding believability without the extra processing requirements of more complex raytracing algorithms. Load the file "CompositeStage3.blend" from the "examples" folder. The nodes will appear empty until you render (F12). Also, it's okay that the dial appears blank right now. The dial is seen through a refractive object and won't show until you make use of the Refract pass later. Figure RCD.15: The Bloom Node network. Viewer nodes have been attached so you can easily examine the various stages. As you can see from the node tree, we have collapsed some of the nodes from the previous section using the controls described earlier. That should make it easier to focus your attention on
the bloom effect. Once you are happy with a section of a complex composite node tree, it is a good idea to collapse it like this to keep clutter to a minimum. Source of the Bloom Although there are several ways to produce a bloom effect, the simple approach we've taken is to use the Specular pass again, brightening it and applying some blur before mixing it back into the existing image. Using RGB Curves to Brighten an Image The network uses an RGB Curves node, taking its input from the same specular pass you used before. In the basic back-shadowing tutorial, you used the RGB Curves node to invert and colorize an image. Here it is used to brighten the Spec pass by drawing the top right point of the Combined curve over three quarters of the way to the left. Figure RCD.16: Here's a neat trick: enable the "Backdrop" button on the Node Editor's header. Now, clicking on a Viewer node shows that preview right in the background of the Node Editor. This is particularly
useful if you are working with your nodes in a Maximized window (Ctrl-Up Arrow/Down Arrow), or if there is no room in your screen layout for a UV/Image Editor window. The backdrop preview may be moved around with Shift-MMB. Figure RCD.17: Backdrop enabled on the header. This preview shows the result of the RGB Curves node on the Spec pass. Blurring an Image After the RGB Curves node, you have a Blur node, which can be found under Add->Filter->Blur. Figure RCD.18: The Blur node with settings for the bloom effect. Although there are seven different blurring styles to choose from, two of the most commonly used are Gauss and Mitch. Gauss Gaussian is a good, general purpose blur. It provides an even effect across the image.
Mitch Mitchell-Netravali blur gives a more accurate effect for bright objects. It does not reduce highlights by evenly spreading them like Gaussian blur. Because of that, this type of blur is excellent for working with highlights, as you are here. Of course, other blur methods like CatRom will produce similar effects, so the choice is yours. With the speed of the Compositor, it's easy to switch between different blur methods to see which works best in your final production. Blur Settings In the previous illustration, the Blur node's X and Y values are set to 35. Above the X and Y settings are two buttons that, although not used here, are worth explaining. Bokeh This is a more complex blur setting that attempts to simulate optical blurring, the kind that would happen with an out-of-focus camera, as opposed to the simple mathematical blurring of other methods. This setting will slow renders and composite updates considerably, but when attempting to fake a camera blur effect, it is much more realistic. Gamma This setting will give bright parts of the blur precedence over darker portions, instead of averaging them. This will usually lead to a brighter blur.
Figure RCD.20: Using the Mix node in Screen mode again. Mixing the Bloom Effect You need to mix this brightened and blurred image with the results of the diffuse and specular combination from earlier. Notice how the title of the Mix node has changed to "Screen," making it easier to tell the mix type at a glance, even on a collapsed node. Figure RCD.21: A new Mix node, in Screen mode. We have used a Screen Mix node (Add->Color->Mix), as once again you have to blend an image that needs to brighten another. In this case, the Factor has been adjusted to 0.37, but try taking it as high as 0.80 to see if you like it better. Reflection/Refraction Adjustment So far, you have improved the look of the metal and added a nice bloom to the highlights. You're still missing the reflection and refraction, though. Load “CompositeStage4.blend” from the disk and render to fill all the buffers and passes.
Figure RCD.22: The additional nodes for reflection and refraction. You have both a reflection and refraction pass available because the brass material uses raytraced reflections and the glass dial uses raytraced refraction. To see what these passes produce, follow the connectors to their associated viewer nodes and select each in turn.