CAP 203 - Computer Animation III

Chapter 5: Reflections

Objectives:

This lesson covers material from chapter 5 of the text. Objectives important to this lesson:

  1. Methods to create a reflection
  2. Shiny surfaces
  3. Observations on reflected light
Concepts:

This is a short chapter dealing with some aspects of reflections. The chapter begins with an observation that shiny objects should reflect other objects in a scene, but making them do so can add rendering time to the scene.

Reflecting on reflections

In the first lesson on page 114, the author promises to present a few techniques for making a surface look reflective. Several are presented, but she spends the most time with the first, which is the easiest. Each successive technique adds more quality to the scene, and more rendering time.

  1. Open the CandyDish scene file from chapter 5. The first thing that may occur to you is that the main object in the scene looks more like a candle holder than a candy dish. Maybe she doesn't put out much candy at one time. The author has already assigned a color to the candy dish object. She directs us into the Material Editor, selects the material assigned to the object, and takes us to the Map channels rollout for the object's material. Note that there is a channel assigned to Reflection, and like the other channels, it has not been used yet. Click the map button for that channel.
  2. The author directs us to choose bitmap on the dialog that comes up. She informs us that the default behavior of 3DS Max is to make this map 100% reflective, removing most of the benefit we would otherwise get from our choice of Diffuse color or Diffuse Map. She advises us to tone down the reflection percentage, which is changed on the map channels rollout. She also advises changing the Specular Level and Glossiness settings, which are changed on the shader parameters rollout for the material. Recall that a larger value for Specular Level means brighter reflected light, and a larger value for Glossiness means a smaller area casting the reflection. Adjust these settings to your taste and save the file incrementally.
  3. The author illustrates the behavior of her reflection map when used on the candy dish and the chrome ball in the scene. She warns that this technique works on these two objects because they have curved surfaces. She does not recommend this technique for the table top in the scene, which is flat.
  4. For the table top, she advises us to use the Reflection channel again, but to use a Flat Mirror material instead of a bitmap. She also advises apply this material only to the polygons on the table that will actually be reflecting objects. This would seem to apply best to tables that are shiny on top, but not on the sides, like many restaurant and office tables.
  5. Step 5 brings us a new, more intensive technique: use a Raytrace map. The author does not recommend it, advising us that we can get similar results with the techniques already described, and that they are quicker to render. She also observes that this was used extensively in previous versions of 3DS Max, so you will encounter it in legacy scenes. Perhaps the subtext is that you will have an opportunity to improve the rendering time of such scenes by changing them to use the first two techniques.
  6. The last method discussed in the lesson is to use Mental Ray materials. Logically, you would also use the Mental Ray render engine for the best results. Each of these choices adds to the render time of a scene, but each also improves the realism of reflected light in the scene.

Bling

This lesson is on pages 116 and 117. The author introduced the idea of using a Raytrace map in the previous lesson, but she did not have you use it. Here she uses it with some other interesting methods for creating her scene.

  1. The lesson begins by making a simulation of a faceted jewel. Begin as instructed, by making a spindle object. She instructs us to weld the center vertices together. Use the regular weld method on the vertices, not the target weld I have had you use in other lessons. In this case, you want the weld method's behavior of placing a new vertex halfway between the locations of the original vertices.
  2. There are no real directions for step 2, only advice to weld vertices and chamfer edges. Look at the resulting faces on her example in this step, and experiment with the two methods. Cross consult with other students and develop a procedure. Note that the result does not need to look exactly like a real jewelers cut.
  3. In step 3, the author tells us that she used a jpg file that comes with 3DS Max, but that she modified it for her use. Sounds like we need to save our scene, and use Photoshop for a few minutes. Once you find the reference image to modify, open it in Photoshop and use good work habits: save a copy in native format, modify the copy as needed, then save the final result as the desired file type with a new name, in a location where you and 3DS Max can find it.
    Once you have done the Photoshop work, continue with the instructions in this step.
  4. The author asks us to make some modifications to the Raytrace material in 3DS Max. Her changes to Luminosity, Transparency, and Index of Refraction are illustrated in the image for this step. Note that you can easily look up IOR values for specific gem types on the Internet, if you are trying to simulate the shine of a particular type of stone.
  5. The author advises us to change some settings for the material to make it look like a gemstone. She means a gem other than a clear white diamond. We have already simulated a cut and a carat weight, so this step attends to color and clarity. (Those are the four Cs of gemstones.) She advises that you should make the specular color a lighter tone than the diffuse and transparency colors for your material. This is good advice for any material. I have not been able to think of a material in the real world that has a specular color darker than the material itself.

Observations on light

On page 120, the author provides some background on light and optics, which may be useful if you are trying to see a reflection in a mirror and are unable to do so. The basic physics statement that applies here is "the angle of incidence equals the angle of reflection". This applies to the illustration on page 121. An alternate illustration appears below.

  • Assume that the horizontal line (the floor of the scene) is the reflective surface.
  • The camera in the scene is on the left, and the object whose reflection we want the camera to see is on the right.
  • The dotted line in the illustration is an imaginary line that is perpendicular to the reflecting surface, drawn at a point halfway between the object and the camera.
  • Consider two angles. The perpendicular dotted line and a line of sight from bottom of that line to the object to be reflected form the legs of the first angle. (Indicated in blue in the image on the right.) This is the angle of incidence: the angle at which light from the object hits the reflector.
    The camera's line of sight to the bottom of the perpendicular line, and the perpendicular line itself form the legs of a second angle. This is the angle of reflection, the angle at which light must come to the camera from the object by way of the reflector.
  • For the camera to see the reflection of the object, the two angles described above must be equal. If they are not, the camera will see something other than the desired reflection.

This is simply a fact of optical physics. Try it with your own eyes, a reflecting surface, and a handy object and you will see that it is true.

The author describes the use of the Place Highlight tool, which may be useful in placing objects so that they can be reflected and so that their highlights may be seen to better effect.