LightWave 3D 8 Lighting Wordware game and graphics library phần 4 ppsx

OpenGL. You can change exactly which lights you want Affect OpenGL applied to simply by deselecting this control on those lights. This button determines whether or not the selected light will illumi - nate objects in your OpenGL Layout. Be aware that OpenGL currently sup - ports a maximum of eight lights. You may have Affect OpenGL activated for 20 lights, but only the eight brightest in the list will affect objects within Layout’s OpenGL View, unless you specify the eight lights you want OpenGL to use by disabling the Affect OpenGL switch in all the other lights. Note that this does not affect ren- dered images in any way but only whether the effects of the selected light are visible in Layout’s OpenGL View. Affect Caustics The Affect Caustics button can actu- ally save you significant render time if you have enabled caustics in your scene because you can eliminate all the lights from caustics calculations except the specific ones involved in the caustic effect. What are caustics? In the real world, caustics are very similar to specularity, except that instead of the light intensifying toward the camera, it reflects off the surface and intensifies on another surface. Caustics is similar to radiosity in that it is light that is reflected off one sur - face onto another or focused by refraction onto another surface. The difference is that caustic light is focused and highly intensified to create a bright area of reflection or refraction. By having the Affect Caustics button enabled only for a specific light or a couple of lights, all other lights will not calculate caustics. This ································· General Light Properties 137 Figure 11.5: Affect OpenGL button. Figure 11.6: The Affect Caustics button. means more predictable results and less render time than if you had caustics enabled for all lights. Note: Caustics must be enabled in the Global Illumination panel. Caustics are pretty render-intensive and finicky so you may find that this is a tool you don’t often use. Of course, render power and speed is always increasing. Not long ago we all thought area lights were too render-intensive to use. Chapter 11 ······································ 138 Figure 11.7 Figure 11.8 Enable caustics both on the individual light (in the Light Properties Basic sub-tab) and in the Global Illumination panel. Figure 11.9: Example of caustics. Intensity Light “intensity” refers to the bright - ness of your lighting instrument or how much brightness it is adding to the objects in your scene; that is, how much light it is putting out. We would consider that a 1000-watt lightbulb has an intensity ten times greater than a 100-watt lightbulb. In the world of real lighting, 0% is where the light is off and 100% is where maximum voltage has been applied, usually 110 volts or 220 volts (or other voltages depending on where you live). Fortu - nately for us, we CG artists are not limited by available electricity. The percentage range of 0% to 100% is by no means an upper or lower limit. Light intensity is a multiplier that is used to calculate the final color of a surface. For instance, if you have a light with an intensity value of 100% aimed exactly perpendicular to a flat colored surface that has an RGB value of 200, 200, 200 and a diffuse value of 100%, the color that will be rendered out is 200, 200, 200. If the light has a value of 50%, you will receive a color of 100, 100, 100. In practical application however, choos- ing the proper intensity value is not always that straightforward, as there are many more calculations involved with varying surface parameters, light angles, etc., that often require you to use values outside the range of 0 to 100. There is no (practical) upper or lower limit to your light’s intensity value. Your light can be 1,000,000% if you like or –38,465%. There is actually a numerical limit to how high or low LightWave will allow you to adjust the intensity, but the values are so extreme that it is generally not practical to use them. Note: Intensity values above 100% and below 0% must be entered numerically. The slider arrows only work from 0% to 100%. What’s the use of a light intensity over 100%? You’ll find that you often use lighting values over 100%. Remember earlier on in the book when I mentioned that lighting levels are completely relative? This is where that principle comes into play. Say, for example, you have a nice interior shot beautifully lit with lamps and diffuse reflections from light sources ································· General Light Properties 139 Figure 11.10: The Light Intensity setting. within the room. Then the client says she wants sunlight streaming in through the window. So you place a light outside the window, crank it up to 100% and render. But you can barely see the light because all the other lights inside are between 50% and 100%. The sunlight should be predominant, but it’s just washed out by all the other lights. Relative to the interior lights, the sun should be many times brighter. So make it many times brighter. Start by cranking it up to 500%. This may be too bright, but it’s a place to start. You get the idea. Intensities are highly subjective. They’re easy to set, and one inten - sity takes pretty much the same amount of time to render as another. Feel free to experiment with wildly strange intensities. Push the limits of your scene to see what your lights are capable of. What about lights of negative intensities? This is a truly great tool that every gaffer in the world wishes he had available on set. A negative light will remove intensity from the scene, resulting in lower diffuse and/or specular values of surfaces illuminated by that light. It can be used like a carving tool, removing only specific light from specific areas of the scene. You can even use a light with a negative value to remove volumetrics from a volumetric light of positive intensity. For example, if I have a surface lit with a distant light at 100% and I aim a spotlight with an intensity of –50% at the middle of the surface, there will be an area in the middle of the surface that is illuminated at only 50%. Chapter 11 ······································ 140 Figure 11.11: Layout View of intensity example. There are a number of practical applications for using negative lights. For one, you can carefully sculpt exactly where you wish your light and dark areas to be in the shot. You can also use a negative light to remove color from another light. For example, white light is composed of the three primaries: red, green, and blue. If you shine a negative green light on a white light, some of the green will be removed, leaving mostly red and blue, or magenta. ································· General Light Properties 141 Figure 11.12: Render of intensity example. Figure 11.13: The main light is a distant light with a color of 255, 255, 255, or pure white. The spotlight has been set to –50% intensity and has a color of 0, 255, 0, or pure green. This means that 50% of the green has been removed from the area where the spotlight is shining. (See color image.) Understanding the color wheel and how to mix colors is key to using this trick effectively. The color wheel and color mixing are covered in detail in Chapter 19. This technique is a great way of coloring your lights without having to compete with the intensity already in the scene. In other words, if all the lights in the room are relatively bright, you don’t have to crank a particular red light up to 1000% just to see some of the red color in that spotlight (or whatever light type you choose). Instead, add a negative intensity and remove the colors you don’t want to see. As another example, let’s say you have a scene perfectly lit, but the color values of the lights aren’t quite right. Perhaps they are too warm for the intended environment. Instead of adjusting the color values of all the lights in your scene, you could add a negative light or two with the proper color values selected to “pull” some of the unwanted color values out of the scene. To be really sneaky, you could also apply a negative Ambient Intensity value with an appropriate color choice to accomplish a global reduction of color values of surfaces in your scene Now just to throw a monkey wrench into the works, if you place an object in front of the negative light, the object will cast a shadow but not one you might expect. In this shadow, the negative light will not have any effect at all on the original surface value. In other words, light will not be subtracted from the area in shadow. Think of it this way: With a “normal” light of positive intensity, there is no light added into an area of shadow. With a light of negative intensity, just the opposite happens — no light is subtracted from the area of shadow. Chapter 11 ······································ 142 Figure 11.14: If the spotlight had a positive intensity value, the shadow area behind the ball would not receive illumination from the spotlight. Since the spotlight has a negative intensity value, the shadowed area behind the ball is not having light removed and you get a sort of “photo-negative” effect. (See color image.) Now to add a second monkey wrench: In LightWave 7.5, we were given the option of coloring the shadows in our scene. This is done in the Light Properties panel Shadows sub-tab. If the light is negative, however, the shadowed area will have the selected shadow color removed. Using our example scene with a nega - tive spotlight colored 0, 255, 0 (pure green), this produces an area in which some of the green has been removed. If we then make the shadow color 255, 0, 0 (pure red), then the shadowed area from the negative spotlight will have some of the red removed, resulting in a shadowed area containing mainly blue and green. Note: Bear in mind that the shadow color setting only changes the color of the shadow cast by one object onto another object. The color of the self shadows on the object are not affected, so you might end up with two different colored shadows beside each other. This severely limits the practical use of shadow color. So you can see how versatile light intensity can be. It’s much more than simple illumination. Intensity can define a light source. The sun, for example, is usually blinding. Put an extremely bright light source in your scene and most people will assume it is the sun. Conversely, if you put a ································· General Light Properties 143 Figure 11.15: This checkerboard polygon is lit with a white distant light. We have added a green negative spotlight that removes the green, resulting in a magenta area (magenta is composed of red and blue). We have also made the shadow of the negative spotlight red; therefore, red is removed from the shadowed area, resulting in a cyan colored shadow (cyan is composed of blue and green). (See color image.) very small, dim source in your scene, people will have no trouble accept - ing that as a candle flame. Experiment with intensity. Try out different relationships. For example, fill light is usually at a lower intensity than the key light. That doesn’t mean it must always be so. Try out different combinations. Falloff Light falloff is probably one of the most important yet subtle properties of your CG light. Let’s begin with a discussion of how falloff works. You know that if you turn your radio on you will hear sound. You know that if you walk away from the radio, the sound will get quieter and that at a certain point, you will be so far away that your ears can no longer perceive any sound from the radio even though it is on, even though the speakers are vibrating, compressing, and rarifying the air molecules in the room. The density of the molecular motion decreases the farther away you get from the speaker and the more the sound spreads out over three-dimensional space. That is sound falloff. It is very similar to how light falloff works. When light is emitted from a light source, a quantifiable number of photons are released. These photons spread out in all directions, becom - ing less dense as they spread out. The farther away from the light source, the lower the density of photons. This means thata1cmsquare piece of paper held very near the light source will be struck by many more photons than the same 1 cm square piece of paper held very far from the light source. Very far away from the light source, only a tiny fraction of the photons reach the 1 cm square piece of paper. This is the reason why stars seem so dim. Many of the stars are much, much brighter than our own sun, yet because of their distance from us, they appear so dim as to be invisible during the day and cast almost no visible light on the earth during the night. Natural falloff is exponential or curved because it follows the inverse square law; in other words, the light is spreading out both horizontally and vertically as it moves away from the light source. To understand this, you must first know that the area illuminated by a light source Chapter 11 ······································ 144 Figure 11.16: The Intensity Falloff setting. corresponds to the square of its distance from the light source. For instance, let’s say that you have a spotlight that has been “barn-doored” to project light in the shape of a square. Furthermore, it is aimed at a surface that is 1 meter away and happens to illuminate an area that is 50 centimeters wide and tall (50 square centimeters). If you were to move the light or the surface so that they are now 2 meters apart, you would get an area of light on the surface that is 100 centimeters square, or four times the previous area (2 squared = 4). Increasing the distance to 3 meters would give you an area of light that is nine times greater than it is at 1 meter apart (3 squared = 9). We know that the farther away a surface is from a light source, the more the same number of photons are spread out, so each time we increase our distance, we have a larger area of light, but it is less bright—sort of like having enough paint to cover a 1 meter square area. If we have to cover 10 square meters with the same quantity of paint, the paint is going to be a lot thinner. Since the area of illumination corresponds to the square of the distance, the inten- sity of the light must fall off by the inverse square of the distance. With our example above, let’s say that the area illuminated at 1 meter away receives 100% of the light. This means that at 2 meters away, the area being illuminated would only receive 25% of the light (the square of the distance is 4 and the inverse of that is ¼, or 25%). As we increase our distance to 3 meters, the area being illuminated would only receive 11.11% of the light value (3 squared = 9, and 1/9 th of 100% = 11.11%). You can see that in nature, we can never actually get to 0% falloff. To actually calculate this in LightWave would take forever and so we are able to adjust the range of lights so they do not illuminate anything after the defined range. Of course, it would take a very long time to model the entire universe to test this, so the point is moot anyway. In LightWave you have the option of choosing other falloff calcula - tions. A linear falloff, for example, means that if you set the range of the light to 1 meter, the intensity will be 100% (or whatever intensity you set) at the light source and 0% at 1 meter away from the light. There will be no illumination outside the 1 meter circle around the light source. At 0.5 meters, the intensity will be 50%, and so on. This is not a physi - cally accurate model of light falloff; however, I have found that few people can look at a falloff gradient and tell whether it’s linear, inverse distance, or inverse square. ································· General Light Properties 145 Figure 11.17 clearly demonstrates the differences in falloff type. The bottom segment shows a natural falloff using the inverse square. This is how real light falls off. But you may not always wish to have that much intensity so close to the light source. You can lower the near intensity by selecting either Inverse Distance or Linear. Or you can decrease the nominal distance. The nominal distance used with inverse or inverse square falloff determines where the light falloff begins, so light within the nominal distance circle will be at the full intensity set in the Light Properties panel. This is an instance in which real-world calculations often don’t seem to be very important. I usually use linear falloff and only occasionally switch to one of the other types. Distant lights are not equipped with falloff. This is because distant lights are meant to simulate sunlight. The sun has falloff just like any other light source, but the amount of falloff occurring within the human perceptual range is so slight as to be virtually unnoticeable. Why calcu - late something that can never be perceived? Chapter 11 ······································ 146 Figure 11.17: Falloff types [...]... render times, and rid yourself of the pesky villagers with pitchforks and torches LightWave creates a radiosity solution by calculating light bounce from one surface to another Rather than giving your CPU all those extra calculations, try turning off radiosity and instead place a lighting instrument where the bounce would occur and pointing in the direction in which the bounce would go Figure 12 .8: Using... located The result is very complex and theoretically very realistic lighting Even using Backdrop Only radiosity the lighting will be much more natural due to the complex colors and shapes of the lighting In feature production, this method can only be used well if HDRI Light Probe (360 degree) images are taken on set so that your CG lighting will closely match the real lighting used there However, if you... locate and download an HDR image, locate and install both HDR Shop and LightGen, and create a text file A few minutes later I had a nice light array in LightWave s Layout and rendered the following image Figure 13.3: LightGen render (See color image.) 167 Chapter 13 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · This technique renders in much less time than HDRI and radiosity;... need only to know the qualities and properties of that bounce, where it originates, what color it should be, and what direction it is going Just treat the bounce as though it were a lighting instrument and proceed accordingly 160 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · Radiosity Baking Radiosity One of the best lighting tools in LightWave is the Surface Baker... character Turn radiosity and the Surface Baker off and render the sequence You will get radiosity lighting on your building walls and still have shadows from the character without the render times of radiosity For more information on the Surface Baker and for details on its use, see the 161 Chapter 12 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · LightWave manual Chapter... important to understand Figure 12 .4: The Rays Per Evaluation this concept because all three setting radiosity types have a pertinent setting that can help speed up render times: Rays Per Evaluation 155 Chapter 12 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · You will notice that rays per evaluation come in many sizes such as 1x3, 2x6, 3x9, 4x12, and so on up to 16x 48 These dimensions... that light will reach the object, even if you point the light directly at it 1 48 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · General Light Properties In LightWave 3D 8, we can now click on the dark gray bar in the Exclude window to access Select All, Clear All, or Invert Selection options This is very handy when you have many items in the scene to select or deselect Figure 11.21:... is that no other lighting tool in the LightWave arsenal will provide you with the photo-realism that radiosity will This is because radiosity behaves more like real light than any of LightWave s other tools Read on and be converted Radiosity Defined Simply put, radiosity is the reflection of light Light comes out of the sun, hits the white concrete in front of your house, bounces up, and hits your yellow... texture, lighting information included, back onto your surface You set your surface luminosity to 100% and your surface diffuse to 0% and voilà You can also bake only the illumination data into the map and apply that on the illumination channel of the texture if you don’t want to lose the advantage of having separate channels of control in your Surface Editor Note: Don’t forget to then turn off radiosity and. .. intensity This chapter has covered numerous capabilities of the lighting tools available in LightWave By now you should have a good grasp of most of the tools discussed herein No doubt there are dozens more that I haven’t thought of, and probably thousands more invented by other artists in times of need Use your creativity to find new, effective, and cheap ways to use these great tools 151 Chapter 12 Radiosity . 12 .4: The Rays Per Evaluation setting. You will notice that rays per evaluation come in many sizes such as 1x3, 2x6, 3x9, 4x12, and so on up to 16x 48 . These dimensions represent the segments and. at it. Chapter 11 ······································ 1 48 Figure 11.20: Excluding objects in the Objects sub-tab. In LightWave 3D 8, we can now click on the dark gray bar in the Exclude window. in LightWave. The primary difference between Backdrop Only and Monte Carlo is that the light is actually bounced from one surface to another along with the sur - face color. In LightWave 3D 7.5