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Tutorials LightWave 3D Lighting Techniques Part 1 Qua Jan 26, 2011 3:14 am
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| by Amaan Akram |
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 PART 1 of 2 (Owing to excessive workload, I've had to split this tutorial up in to two parts. The next part will cover outdoor and indoor lighting and general techniques for a 3D artist) The goals of lighting in 3D computer graphics are more or less the same as those of real world lighting. Lighting serves a basic function of bringing out, or pushing back the shapes of objects visible from the camera's view. It gives a two-dimensional image on the monitor an illusion of the third dimension-depth. But it does not just stop there. It gives an image its personality, its character. A scene lit in different ways can give a feeling of happiness, of sorrow, of fear etc., and it can do so in dramatic or subtle ways. Along with personality and character, lighting fills a scene with emotion that is directly transmitted to the viewer. Trying to simulate a real environment in an artificial one can be a daunting task. But even if you make your 3D rendering look absolutely photo-realistic, it doesn't guarantee that the image carries enough emotion to elicit a "wow" from the people viewing it. Making 3D renderings photo-realistic can be hard. Putting deep emotions in them can be even harder. However, if you plan out your lighting strategy for the mood and emotion that you want your rendering to express, you make the process easier for yourself. The overall thrust of this writing is to produce photo-realistic images by applying good lighting techniques. I will use Lightwave 3D to demonstrate the lighting techniques used, but these techniques can be applied in any 3D software. COMPONENTS & PROPERTIES OF LIGHT Each light source can be broken down in to 4 distinct components and analyzed accordingly.
I consider the abovementioned terms to be self-explanatory, but I will give some description of each in the following text. Some people combine all these terms under another term which they refer to as "Quality of Light". This quality of light is determined by the contribution of each of these 4 components towards the overall lighting within a scene. I would like to give a few examples here from the world of photography. As I have discovered, photographers are masters of lighting and there is much to be learned from their work. For example, the quality of light varies from time to time in a natural environment, and photographers choose their subjects according to the quality of the available light at a given time during the day. Some photographers shoot only after dawn and just before sunset because the light at these times of the day has stronger colors, and casts long, dramatic shadows. You can simulate this kind of environment inside your 3D software and get some really dynamic renderings. Low-angled incoming light is good for sidelighting, which gives a good overall three-dimensional quality to your subjects. Backlighting them with similar lights can create outstanding silhouettes. I often light my characters using low-angled lights that create long shadows and highlight the form of the character. This kind of lighting is also very good for landscapes, so try such a lighting setup in your next landscape rendering. In overcast lighting conditions, such as a cloudy day, photographers shoot close-ups of flowers, for example. Overcast lighting translates to a light source of considerable area (Area light source in Lightwave). Other examples of photography that can be shot in overcast conditions (or with a big area light source) are portrait photography and food photography. These don't necessarily have to be done outdoors. The operative phrase here is "Big Area Light Source." I shall now individually describe each of the 4 components of light. LIGHT INTENSITY Intensity of light can simply be defined as the amount of light being emitted from a source of light. As you increase a light's intensity from zero (off)to very high values, interesting things start to happen to the objects being lit by such a light. Below is a series of images that show some of these effects. I wanted to highlight a sphere placed between some objects, and I analyzed the effects of changing the intensity of the light in the scene on the overall composition. <table align="center" border="0" cellpadding="2" cellspacing="2"> <tr align="center" valign="middle"> <td>  fig. 1.1 </td> <td>  fig. 1.2 </td> <td>  fig. 1.3 </td> </tr> <tr align="center" valign="middle"> <td>  fig. 1.4 </td> <td>  fig. 1.5 </td> <td>  fig. 1.6 </td> </tr> <tr align="center" valign="middle"> <td>  fig. 1.7 </td> <td>  fig. 1.8 </td> <td> </td> </tr> </table> Fig. 1.1 is very under lit and you can barely see the reflection of the light source. Fig. 1.2 could still benefit from a stronger lightsource. A sphere reflecting the light source is now visible. Fig. 1.3 shows most of the objects in the scene, but doesn't make a strong statement. Textures are beginning to emerge. Fig. 1.4 shows almost all the objects in the scene. Note that you no longer see the reflection of the light source, and the texture on a third of the sphere has been lost. Fig. 1.5 brings out all the objects in the scene in a clear manner. The sphere's colors are now over-saturated because of the stronger light (compared to Fig. 1.3) Fig. 1.6 shows that the objects surrounding the central sphere are beginning to get over-exposed to light, and their colors begin to saturate. Fig. 1.7 simply intensifies the effects mentioned in the description of Fig. 1.6. Fig. 1.8 represents wildly over-saturated colors and overly bright objects with a considerable amount of texture and foreground lost to over-exposure. If we continue to analyze this series of pictures, we'll notice that the contrast between the sphere and its surrounding objects is very much balanced in Fig. 1.5 as the surrounding objects are nicely lit and the profile of the sphere can be clearly recognized. In Fig. 1.8, however, you'll notice that the sphere no longer has a central role, leading to weaker composition. That being said, there are occasions where over-exposure may be very desirable. It all depends on how you want to present an image, and if over-exposure to light brings out some of the subject's stronger features, then by all means do as you want. LIGHT DIRECTION Imagine a scene where there's light of equal intensity and color is incident on a human face from all directions, and the background is black. What would you see? You would just see the 2-dimensional outline of the face. Why? Because light rays of the same color and same intensity will 'paint' all sides of the face with the same color with the same intensity. If a shadow were to be formed, it would be washed out instantly by light rays incident upon the shadowed region. The point that I am making here is that the reason we are able to recognize the shape of an object is because light rays of different intensities hitting the object from different directions 'paint' the object with highlights and shadows. The direction of incoming light from a light source can enhance the shape of the subject and the overall emotion in the scene. It can also ruin what you are trying to capture in the image. To give depth to the object being lit, place the primary light source, or key light, at a certain angle to the camera to bring out highlights and shadows. Doing so will create or enhance the illusion of depth in your object by having a graduated fall off from bright to dark over the surface of your object. What you see on the monitor is actually a two dimensional image, and the illusion of three dimensions is created by highlights and shadows in your object. To illustrate this point further, consider the two rendered images below. <table align="center" border="0" cellpadding="2" cellspacing="2"> <tr align="center" valign="middle"> <td>  fig. 2.1 </td> <td>  fig. 2.2 </td> </tr> </table> Fig 2.1 shows the object being lit from a single light source placed at the left of the camera. You can clearly see the folds, the buldges and the depressions on the surface. You can also clearly see the base of this object touching the ground and casting a shadow. Fig 2.2 represents the same object, but the light source is directly behind the camera. Frontal details are almost lost because the cast shadows in 2.1 have been washed out by the direct light. Some detail, however, on the edges is still visible. It also looks...very boring in my opinion. The direction of incoming light also has an effect on the mood of the image. Following is a typical example of a face being lit from below, giving a very dramatic effect. Consider the two images below. Each shows light coming in from beneath the character's face, but from different directions and each brings out the personality of the character in different way. Fig 3.1 directly brings out the menacing personality of the character, whereas Fig 3.2 brings it out in a subtle way. <table align="center" border="0" cellpadding="2" cellspacing="2"> <tr align="center" valign="middle"> <td>  fig. 3.1 </td> <td>  fig. 3.2 </td> </tr> </table> We are not very used to seeing such kind of lighting. Outdoors, light comes primarily from the sky above us and indoors we place lights either on ceilings or on walls. Light coming from almost directly below the face can 'hurt' the eyes of the subject because usually in such a situation, the light source is directly visible to the human eye. In most cases, we try not to look directly in to a light source. Seeing a character who is comfortable with such direct light--with facial features being brought out in uncommon ways--does have a dramatic impact upon our perception of the personality of the character. If you think of light coming from above as positive light, light coming from below can be considered as the inverse of that positive light, and it reduces the character's positive traits. However, not all situations in which light is coming from under the face are negative. I'll mention here a typical example of a scene where light coming from below (like a warm redish glow) gives a romantic look. While lighting faces, or even an entire character, keep in mind what features of the character define his/her personality. If we observe the character in figures 3.1 and 3.2, we will notice that the personality of the character is defined by his long face, his heavy brows and cheek bones, his somewhat small eyes etc. All these features give his personality a negative touch. But his nose, for example, is very ordinary. Every character has certain features that, when highlighted, have either a negative or a positive influence on the character's personality. These positive and negative features can be highlighted with the appropriate kind of lighting. If you look at the same character in Fig. 2.1, and then compare the personality which is being defined in Fig 3.1, you will notice that there's a big difference in the readibility of his emotions. Fig 2.1 makes him look like a bit of a thinker (with a muscular bod). Almost all the negative features of his face which I just mentioned (the heavy brows and the cheek bones etc.) are not very well picked up by the lighting setup in Fig 2.2, and even in Fig 2.1. In short, light your character to bring out or enhance his/her personality. There can be situations where you may want to hide the negative features of a character to make him or her look innocent. In such a situation, directing your lights in such a way that the negative shadows of prominent features are washed out may help achieve the desired purpose. Light coming from directly above a person's head was often used by Renaissance painters to depict divinty and spirituality. However, the effect of such light is greatly dependant upon the subject. Check out figures 4.1 and 4.2. While the negative aspects of his face have certainly been muted to a great extent, they have not gone away completely. <table align="center" border="0" cellpadding="2" cellspacing="2"> <tr align="center" valign="middle"> <td>  fig. 4.1 </td> <td>  fig. 4.2 </td> </tr> </table> Figures 4.3 and 4.4 again show situations of light coming from top, but not having any 'angelic' effect. The difference between figures 4.1 and 4.2, and 4.3 and 4.4 is that the latter have more localised concentrated and harsh light spots. Such harsh and localised light (along with harsh shadows) is adding to the negative side of this character. <table align="center" border="0" cellpadding="2" cellspacing="2"> <tr align="center" valign="middle"> <td>  fig. 4.3 </td> <td>  fig. 4.4 </td> </tr> </table> LIGHT COLOR I stated earlier that the reason we are able to recognize the shape of an object is because light rays of different intesities hitting the object from different directions 'paint' the object with highlights and shadows. To make this statement more complete, I'd have to add here that our ability to recognize the shape of an object depends upon the ability of light rays of different intensities and different colors hitting the object from different directions to 'paint' the object with highlights and shadows. The color of incident light depends upon its source. White light is composed of all the possible colors that exist. A ray of white light changes color if it encounters an obstacle, which is not white and is not black. If it hits a white object, the same ray is reflected. If the object is black in color, the object absorbs all the light, no matter what color it was originally, and nothing is reflected. So basically when you look at a totally black object, you see the color black because no light enters your eye from that direction. To prove this point, I ask you to close your eyes for one second (and please try not to doze off). Now...which color did we see? In Fig. 4.5 below you can see a white incident ray of light, which is reflected off a blue floor. The floor absorbs all the colors in the incident ray except blue, and reflects it. Note that the light is reflected at the same angle at which it was incident relative to the floor.  Fig. 4.5 Other things being equal, any object that is in the path of this reflected blue ray will be lit by blue light only. Furthermore, the ability for a color to reflect light depends on its brightness and richness. Bright red, for example, will bounce off more light than dark blue. Different colors also convey spatial and temporal relationships. OK. Lemme explain what those fancy words are. A spatial relationship is based on the distance (or space) between two or more objects. A temporal relationship is based on time. (Ever heard the phrase "temporal displacement" in Star Trek?) The color Blue is often used to represent depth. Just take a look at any TV/film and all night time filming will have a slight blue tint. An object lit with the darker (less saturated) shades of blue generally has a tendency to stay in the background. Generally speaking, saturated colors represent close proximity, whereas unsaturated represent distance. A good example to quote here is foggy/misty mornings. As objects recede in to the distance, they tend to lose their color saturation. To sum it up, brightly saturated colors tend to stay in the foreground, and less saturated colors find their place in the background. Take a peek at the following three figures (5.1-5.3) of Gramps (modeled and textured by David Maas). All these images were tinted with different colors in Photoshop, and each represents a different time of the day. Even though the shadows don't change position through each of these three images, a different point in time during the day is depicted by each. <table align="center" border="0" cellpadding="2" cellspacing="2"> <tr align="center" valign="middle"> <td>  fig. 5.1 (Early Morning) </td> <td>  fig. 5.2 (Mid-day-winter) </td> <td>  fig. 5.3 (evening-summer) </td> </tr> </table> Mornings usually have a blue tint. Around mid-day, you get more or less even colored light. There is some blue light present (reflected from the sky), but its effect is not as much pronounced. Evening light is typically characterized by warm, orange hues. Gaze upon the next set of three images. The shadows change positions in the first two. Fig. 5.4 represents summer mid-day again, and 5.5 represents evening time. Fig 5.6 depicts a scene lit by a moon high in the sky. The blue tint is there to give the illusion of night time. <table align="center" border="0" cellpadding="2" cellspacing="2"> <tr align="center" valign="middle"> <td>  fig. 5.4 </td> <td>  fig. 5.5 </td> </tr> <tr align="center" valign="middle"> <td colspan="2">  fig. 5.6 </td> </tr> </table> LIGHT SOURCE SIZE The size of the light source has a major effect on the overall feeling of the scene. A small sized light source casts very sharp and distinct shadows, bringing out the element of tension in the image. An example of a light source small in size would be a flashlight's bulb and it does indeed cast very sharp shadows. A light source occupying a bigger area casts a much softer (less distinct) shadow, and brings a relaxed feeling to a scene. Fix your eyes on our familiar Mr. Gramps in figure 6.1 below for a moment. You will realize that his face is lit from a very small, concentrated source of light that casts very distinct shadows, most noticeable under the nose and the brows. The light source brings out the sadness, hopelessness in the scene in a much stronger way than in figure 6.2. Both figures are lit from light sources placed above Gramps, but the light source in 6.2 is much bigger (evident from the soft shadows) than the one in 6.1. <table align="center" border="0" cellpadding="2" cellspacing="2"> <tr align="center" valign="middle"> <td>  fig. 6.1 </td> <td>  fig. 6.2 </td> </tr> </table> The softer/bigger light source in 6.2 almost gives Gramps an element of hope that is missing in 6.1. He looks sad, but hopeful (note that both 6.1 and 6.2 use the same Gramps, with the same facial expression). END OF PART I Part II coming soon  Amaan Akram - [Tens de ter uma conta e sessão iniciada para poderes visualizar este link] - [Tens de ter uma conta e sessão iniciada para poderes visualizar este link] Special thanks to David Mass of the order of STICKMAN, for his support and feedback, and of course, for Gramps. |
