1 / 24

Specular Reflection

Specular Reflection. Lecture 27 Mon, Nov 10, 2003. Specular Reflection. The intensity of specular reflected light varies with direction. The maximum intensity is in the “ideal” direction. Angle of reflection = angle of incidence. Specular Reflection.

alyssa-obrien
Download Presentation

Specular Reflection

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Specular Reflection Lecture 27 Mon, Nov 10, 2003

  2. Specular Reflection • The intensity of specular reflected light varies with direction. • The maximum intensity is in the “ideal” direction. • Angle of reflection = angle of incidence.

  3. Specular Reflection • Specular reflection creates the appearance of “shininess.” • Surfaces with a high specular reflection appear very shiny. • Surfaces with a low specular reflection appear matte.

  4. Example • LampShader.exe

  5. Blinn and Phong Lighting • OpenGL uses the Blinn lighting model of specular reflection. • However, we will first study the Phong lighting model since it seems more natural.

  6. Phong Lighting • The intensity of the reflection is a function of the angle between the viewer and the ideal direction r of reflection of light from the light source off the surface.

  7. Phong Lighting Light Source Eye Ideal Direction n r s v    P Surface

  8. r s n s r   Phong Lighting • To compute r, note that r + s equals twice the projection of s onto n.

  9. Phong Lighting • The projection of s onto n is (sn)/(nn)n = (sn)n • Therefore, r + s = 2(sn)n and r = –s + 2(sn)n

  10. Computing Specular Reflection • According to the Phong lighting model, the specular reflection is proportional to the cosine of the angle between v and r, raised to a power (called “shiny”). • This is calculated as (rv)shiny

  11. Computing Specular Reflection • Two other factors are • Intensity of the incident light. • 0  Ls  1. • Specular property of the surface. • 0 ms  1. • The formula for specular reflection is rs = Lsms(rv)shiny

  12. Computing Specular Reflection • Of course, if sn < 0 or if rv < 0, then rs = 0. • Why?

  13. Blinn Lighting • A slightly more efficient method is the Blinn lighting model. • Let h be the halfway vector, the unit vector halfway between s and v. • Use hn instead of rv. rs = Lsms(hn)shiny

  14. Blinn Lighting Light Source Eye Halfway n h  s v P Surface

  15. Blinn Lighting • How does hn compare to sv? • If s, n, and v are coplanar, then the angle between h and n is half of the angle between s and v. • Why is Blinn lighting more efficient? • h is computed as h = (s + v)/|s + v|. • This is more efficient to compute than r.

  16. Emissive Lighting • Emissive lighting is light that emitted by the surface itself. • It is used for objects that are meant to glow. • It is independent of all light sources and directions. • Let me be the intensity of the emissive light.

  17. Computing the Shade of a Surface • The total reflection from a point is the sum of the ambient, diffuse, and specular reflections and the emissive light. sama + Lama + Ldmd(sn) + Lsms(hn)shiny + me

  18. Lighting in OpenGL • Since the diffuse and specular reflections depend on light sources, there is a separate contribution for each light source. • OpenGL provides up to 8 light sources. • Furthermore, there is a separate color component for each type of light. • Red, green, blue.

  19. The Lighting Model • The complete formula for n lights is I = (sarmar + sagmag + sabmab) + 0…n(Larmar + Lagmag + Lagmag) + 0…n(Ldrmdr + Ldgmdg + Ldbmdb)(sn) + 0…n(Lsrmsr + Lsgmsg + Lsbmsb)(hn)shiny + (mer + meg + meb).

  20. The Lighting Model • For each color, the computed value is “clamped” to the interval [0, 1]. • If the value exceeds 1, then it is set to 1.

  21. Gouraud Shading vs. Phong Shading • Gouraud shading computes the specular reflection only at the vertices and then interpolates. • This guarantees that the brightest reflection will be at a vertex (or along an edge).

  22. Gouraud Shading vs. Phong Shading • Phong shading interpolates (and normalizes) the normal vectors and then uses them to compute the specular reflection at each vertex. • Phong shading is • much more realistic. • much less efficient.

  23. Gouraud Shading vs. Phong Shading Gouraud shading. dim interpolated reflection dim reflection dim reflection

  24. Gouraud Shading vs. Phong Shading Phong shading. bright reflection dim reflection dim reflection interpolated vectors

More Related