Essential Blender- P20

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Nội dung Text: Essential Blender- P20

Well, there she is. My, but you look lovely this evening Suzanne!
Chapter 11: Lighting: Discussion By Mathias Pedersen While good lighting has some technical aspects to it, it is largely artistic, based on observation and interpretation. Looking at the way light behaves in real life is the only sure way to achieve convincing results in 3D. Find all the references you can. Don't rely on your memory for the little details - there will always be something that you failed to notice. Light in 3D is comparable to the light you experience in the real world. Light illuminates objects so that you can see them. In the real world, light sources cast rays of light into space that are eventually reflected back to your eyes, enabling you to see the world. In Blender, each surface that is seen by the camera receives a certain amount of light from each of the Lamps in the scene, allowing the camera to render those surfaces. Why is lighting important? Obviously, if there is no light in your scene, you'll get a completely black render. Of course, even bad lighting can fix that. Second, and more importantly, lighting can help to bring out details in your scenes. And third, lighting sets the overall tone and mood for a scene. Great lighting can evoke drama and emotion in an otherwise static scene, while poor lighting can ruin the most carefully designed meshes and materials. Lighting can either help you convey your message, or not. Basic tools Blender comes with a set of basic lighting features that you need to be familiar with before you can focus on their more artistic aspects. Lamps are added like other Blender objects, through the toolbox.
Figure LD.01: Adding a lamp from the toolbox. All the lamp types share a basic set of controls on the Lamp panel.
Figure LD.02: crop of Lamp buttons, with Lamp controls highlighted. Energy: The Energy slider determines the actual brightness of the lamp. RGB: The RGB sliders set the color of the light that comes from the lamp. The color swatch below the sliders can also be LMB clicked to bring up the color picker. Layer: This button restricts light from the lamp so it only affects objects on the same layer. If you wanted to make one object in a night scene appear much brighter than others, it could be placed on a separate layer and lit with layer-restricted lamps. Negative: Sometimes you need to actually subtract light from an area. Using the Negative setting inverts the effects of the lamp, taking light away. No Diffuse/Specular: Prevents either the Diffuse or Specular render calculations from recognizing the lamp. Non-key lights can have their Specular components turned off to avoid visual confusion in a scene. Lamp types
Blender is equipped with 5 lamp types -- lamp, sun, spot, hemi and area -- each with unique purposes and uses. Once a lamp has been added to a scene, its type can be changed using the buttons on the Preview panel. Lamp The Lamp type is Blender's basic light. It works very much like a real light bulb, shining in all directions. The Lamp has a few options, and most repeat themselves in the other lamp types. The standard lamp can cast shadows using raytracing, a very accurate technique that produces sharp- edged shadows. Sun The sun type is a "directional" light. This means that all shading from this lamp appears to come from parallel light rays, as though they were emitted from an infinitely distant, infinitely large object. Although the real sun is neither of those things, its size and distance relative to the Earth make it appear to be so for all practical purposes. Sun Lamps can only cast shadows using raytracing. Figure 2.1 01: Standard Lamp.
Figure 2.1 02: Sun Lamp. The difference between the shadows of an ordinary lamp (left) and a Sun Lamp (right). Notice how the Sun Lamp casts parallel shadows. Spot The Spot Lamp is very much like a real world spot light. It illuminates objects within a controllable cone-shaped area. It also has the benefit of a different method of shadow calculation: buffered shadows. This is handy if you want to have softer shadows than those produced by the common raytracing method, but don't have time to wait for the soft raytraced shadows of Area Lamps. Hemi The Hemi Lamp is a little different than the other light types, as it doesn't have any form of shadow calculation. It functions as a big, illuminating half-sphere surrounding the scene. Hemi Lamps are useful for giving a scene an overall color tone.
Area Area Lamps are the most realistic lights in Blender, but have the drawback of involving more in- depth calculations during shadowing, leading to longer render times. When you need soft and realistic shadows, the Area Lamp is the one to use. In the real world, no shadows are completely sharp, even in direct sunlight. They get softer the farther away they get from the shadow-casting object. Figure 2.1 03: Standard Lamp.
Figure 2.1 04: Area Lamp. The difference between the shadows of an ordinary Lamp (left) and an Area Lamp (right). The shadows of the area lamp blend out the farther away they fall, exactly the way they do in real life. Shadows are enabled and controlled in the Shadow and Spot panel.
Figure LD.03 Ray Shadow: Using shadows based on raytracing is pretty much "fire and forget." Press the "Ray Shadow" button, and make sure that the "Ray" option is enabled on the Render panel of the Scene buttons (F10). Ray-based shadows are perfectly crisp and are slower to render than the other shadow method. In addition to the standard lamp controls, both Spot and Area Lamps have additional capabilities and settings. Controls That Only Apply to Spot Lamps
Figure LD.03.s: The Buffered Shadow options for Spot Lamps. Buf.Shadow: A non-raytracing method of generating shadows. Buffered shadowing creates a special type of image from the point of view of the lamp, then maps it onto the objects in the scene to simulate shadows. Many of the controls on this panel are used to fine-tune shadow map creation. The most important are: ShadowBufferSize: The resolution of the shadow buffer "image." The higher the resolution, the more detailed the shadow can be. If you see pixelization around the edges of your buffered shadows, try raising this value, 1,000 at a time, until you get acceptable results. Bias: Corrects for problems around edges of objects and with objects that might be too thin to be seen by the shadow mapping calculations. Reduce the Bias value if light seems to be leaking through your object, or if the shadow doesn't come the whole way to the base of your object. Soft: One of the great advantages of buffered shadows is that they can be blurred using this setting. Soft shadows can add realism to a scene. If you are planning to raise the Soft value to blur shadows, you will have to also raise the Samples value to prevent ugly artifacts.
Buffered Shadow dropdown menu: Choose from "Irregular," which doesn't allow blurring, or "Classic-Halfway," the default method. Ignore "Classic" - it's only there to support older files. SpotSi: Spot Size. This control sets the angle that the Spot Lamp covers. Although it can be set as high as 180 degrees, shadow mapping at very high values will be mostly useless. The Spot Size is visualized by the cone attached the Spot Lamp in the 3D view. For best results with buffered shadows, try to keep the Spot Size as small as possible while still covering all the objects it needs to light. SpotBl: Spot Blur. This value determines how hard or soft the edge of the Spot Lamp's circle of light will be. A value of 0.0 gives a very sharp edge, like a spotlight on a stage. Setting it to 1.0 results in a gradual reduction in light from the very center of the lamp, with no visible edge. ClipSta, ClipEnd: Objects can only be seen by the shadow creation process if they fall within a certain distance from the Lamp. The ClipSta (Start) and ClipEnd (End) values define this distance. They are visualized by the central line extending away from the Spot Lamp. Although you can set these manually, you can also click the "Automobile" button beside each control to have Blender determine the optimal values for objects within the light cone. Controls That Only Apply to Area Lamps
Figure LD.03.a: The Area Lamp options. As mentioned above, Area Lamps are capable of producing soft shadows with raytracing. There are two settings that control this. The Size spinner on the Lamp panel controls the actual apparent size of the light source. It is visualized by the square panel in the 3D view. The larger the light source, the more quickly the shadow will diffuse as it moves away from its casting object. This can also be changed to Rectangle, allowing you to adjust the vertical and horizontal sizes of the Area Lamp independently. Once you press the Ray Shadow button, several new controls appear. Samples: This controls the quality of the blur effect. Very low values will produce obvious artifacts that look like several hard-edged shadows overlaid and slightly offest. Higher values (up to 16) produce progressively smoother shadows, but can drastically slow render times. Dither: The dither button applies a little bit of noise to the sampling, resulting in smoother shadows.
Remember when working with Area Lamps that they are tuned to have their Energy setting work optimally at the Dist (Distance) setting, shown by the line extending away from the lamp in the 3D view. Objects significantly nearer the lamp than this distance will receive much more energy. Ambient Occlusion (A.O.) Ambient occlusion approximates the lighting conditions of an overcast day, where light comes equally from all directions. This gives very soft shadows and darkens corners and places where objects are close to one another. Used alone, it does look very much like an overcast day, resulting in a flat, boring render. But used as a supplement to standard lights, it adds a great touch of extra realism. Without AO, very careful and complex lighting is needed to give the right shading and shadowing to objects that touch each other. It can be difficult to get correct, and even a couple of little mistakes can ruin the believability of your scene. The inclusion of AO can go a long way toward fixing this. Figure 2.2 01: A render lit only by Ambient Occlusion. The Ambient Occlusion panel is found in the World buttons (F8). One control to check out on the
AO panel is the "Plain/Sky Color/Sky Texture" series of buttons. These let the AO calculations use the color of your world background (which can even be an image) to determine the color of light coming from that part of the sky, and can add even greater realism and interest to a scene. Another good way of giving ambient occlusion more color is to use it along with low intensity colored Hemi Lamps. Light in animation Lights can be animated just like any other object in Blender. In addition to animating the location and rotation of lamps like standard objects, though, a lamp's color and energy can be animated, as well as Spot Size for Spot Lamps and Size for Area Lamps. Key frames are created for lamp settings by pressing the I-key with the mouse over the Lamp buttons and choosing the appropriate key type from the menu that pops up. Ipos for lamp settings can be adjusted exactly like Ipo curves for standard objects, as shown in Chapter 3. Lighting techniques and methods Three point lighting Three point lighting uses three light sources to light a scene (hence the name). The first and most important light is the key light. The key light can be positioned anywhere in a scene and sets the general mood. It is followed by the fill light, which does very much what its name says: fills out the areas not touched by the key light. The last light, the back light, is placed behind the subject, often a bit to either the right or left, and gives a nice highlight around its edges. The highlight visually separates the subject from the background. As it is a widely used technique, there is plenty of detailed information on three point lighting available on the Internet and in other resources.
Figure 4.1 01: Rendered with a three point lighting setup.
Figure 4.1 02: Three point lighting in the GUI. The law or merely a suggestion? It has become a common notion that the three-point setup is "the way to go" when lighting in 3D. It really works better as a guideline, though, than as an ironclad rule. Following it to the letter won't automatically make for good lighting in your scene. Unfortunately (or fortunately depending on how you look at things), lighting is about thinking for yourself. There are not any final rules or complete recipes, just guidelines, tips and techniques. Is three-point lighting even good at all? While it's hard to doubt that it has some useful elements, its status as a superior way of lighting is probably unjustified. It tends to look unnatural, which can make it hard for spectators to connect with a scene. Also, it has come to be associated in viewers minds with studio interviews, making its appearance elsewhere feel odd. What follows is a general approach for lighting that might possibly lead you to a three-point setup if the situation demands it, but will most likely produce a much more organic solution for your scene. Generic lighting
"Generic Lighting," to coin a term, relies on common sense, reality and some basic theories of light. You are not constrained to three light sources here. You can have as many, or few, as needed. If the lower right corner of your image is not bright enough, you add a light or two there. In real life, complex rigs might be necessary to achieve such a little enhancement, but in 3D, there is no cost to adding a little lamp in a corner. Think realistically If you're creating an image that is supposed to take place around midday, think realistically. For instance, setting the Sun Lamp too low in the sky wouldn't be realistic. Neither would it be if you had two Sun Lamps lighting things from opposite directions. Don't laugh - we've all seen rendered images from artists that just look horrible, and it's often because of nonsensical setups like that. As humans we're used to seeing things in real life, and keeping within the boundaries of what we're used to actually seeing will make your lighting look better. If you have two Sun Lamps in an image, it just won't feel right. Keeping it down to one Sun Lamp in a scene, and making all other lights more diffuse and soft will look much better. Keep it looking real. It doesn't have to be exact, which is called photorealism. But it should be believable. Light tracing and bouncing In real life, light bounces off surfaces. Take a typical room as an example. Light comes in the window and hits the floor, but doesn't stop there. It bounces off the floor, illuminating the walls and ceiling. In Blender's renderer, when a lamp illuminates a surface, the light dies there. It does not go on to reflect to other objects. So, in 3D, you would have to fake this bouncing effect by putting a lamp where the light hits the floor, at a lower intensity, so it can cast more "reflected" light around the room. This method can be expanded as far as you like, and light can be traced multiple times. With this technique, though, less is often more, and only one or two bounces will be needed to give your scene believability.
Figure 4.2 01: A lamp has been added to the floor to simulate the way the reflected sunshine lights the room. Single-point lighting "Single-point lighting" is a good term for setting up a single light source, then letting ambient occlusion take care of illuminating the rest of the scene. It causes longer render times due to AO's relative lack of speed, but can get good results with very little work. Some people find this rather easy method to be "cheating." Of course, another way to approach that is to say "If it looks good, it worked!" While this method gives passable results, getting the last bit of believability out of your scene will take a little more work. Circle light Using a circle light is a way of faking ambient occlusion. It doesn't give quite as nice a result as AO, but can still be useful to some extent. To do this, place a number of lamps in a circle in the scene, a little above everything that needs to be lit, and render.
Note: To quickly and easily place lamps in a circle try parenting a single lamp to a circle mesh with Dupliverts turned on in the circle's Object buttons (F7). Figure 4.3 01: Rendered with a circle of lights, set to Ray Shadow.
Figure 4.3 02 Note: If you find the hard-edged raytraced shadows in the illustration disturbing, try using soft buffer shadows instead. With a little work put into making the spots focus on the scene, this can turn out even better as a fast, faked Ambient Occlusion.