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[MTL] illum modes

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Paul Gerarts edited this page Jun 26, 2017 · 5 revisions

The illumination models are

Uvec[i] = bisector(LightVector[i], ViewVector)

fresnelLight() = FresnelReflectance (
                     LightVector[LIGHT] * Uvec[LIGHT],
                     mat.specular,
                     mat.shininess
                 ) * Intensity[LIGHT]

fresnelFinal() = FresnelReflectance (
                     SurfaceNormal * ViewVector,
                     mat.specular,
                     mat.shininess
                 ) * reflection()

  1. This is a constant color illumination model. The color is the specified Kd for the material. The formula is:

    color = mat.diffuse

  2. This is a diffuse illumination model using Lambertian shading. The color includes an ambient constant term and a diffuse shading term for each light source. The formula is:

    color = mat.ambient * ambientLight
    + { SUM FOR_EACH_LIGHT : diffuse() }

  3. This is a diffuse and specular illumination model using Lambertian shading and Blinn's interpretation of Phong's specular illumination model (BLIN77). The color includes an ambient constant term, and a diffuse and specular shading term for each light source. The formula is:

    color = mat.ambient * ambientLight 
    + mat.diffuse { SUM FOR_EACH_LIGHT : diffuse() }

    + mat.specular { SUM FOR_EACH_LIGHT : specular() }

  4. This is a diffuse and specular illumination model with reflection using Lambertian shading, Blinn's interpretation of Phong's specular illumination model (BLIN77), and a reflection term similar to that in Whitted's illumination model (WHIT80). The color includes an ambient constant term and a diffuse and specular shading term for each light source. The formula is:

    color = mat.ambient * ambientLight
    + mat.diffuse { SUM FOR_EACH_LIGHT : diffuse() }

    + mat.specular (
        { SUM FOR_EACH_LIGHT : specular() }
        + reflection()
    )

  5. The diffuse and specular illumination model used to simulate glass is the same as illumination model 3. When using a very low dissolve (approximately 0.1), specular highlights from lights or reflections become imperceptible.

    Simulating glass requires an almost transparent object that still reflects strong highlights. The maximum of the average intensity of highlights and reflected lights is used to adjust the dissolve factor. The formula is:

    color = mat.ambient * ambientLight
    + mat.diffuse { SUM FOR_EACH_LIGHT : diffuse() }

    + mat.specular (
        { SUM FOR_EACH_LIGHT : specular() }
        + reflection()
    )

  6. This is a diffuse and specular shading models similar to illumination model 3, except that reflection due to Fresnel effects is introduced into the equation. Fresnel reflection results from light striking a diffuse surface at a grazing or glancing angle. When light reflects at a grazing angle, the mat.specular value approaches 1.0 for all color samples. The formula is:

    color = mat.ambient * ambientLight
    + mat.diffuse { SUM FOR_EACH_LIGHT : diffuse() }

    + mat.specular ({ SUM FOR_EACH_LIGHT : specular() * fresnelLight()} + fresnelFinal())

  7. This is a diffuse and specular illumination model similar to that used by Whitted (WHIT80) that allows rays to refract through a surface. The amount of refraction is based on optical density (Ni). The intensity of light that refracts is equal to 1.0 minus the value of mat.specular, and the resulting light is filtered by mat.transmissionFilter (transmission filter) as it passes through the object. The formula is:

    color = mat.ambient * ambientLight
    + mat.diffuse { SUM FOR_EACH_LIGHT : diffuse() }

    + mat.specular ({ SUM FOR_EACH_LIGHT : specular() } + reflection())

    + (1.0 - mat.specular) mat.transmissionFilter * refraction()

  8. This illumination model is similar to illumination model 6, except that reflection and transmission due to Fresnel effects has been introduced to the equation. At grazing angles, more light is reflected and less light is refracted through the object. The formula is:

    color = mat.ambient * ambientLight
    + mat.diffuse { SUM FOR_EACH_LIGHT : diffuse() }

    + mat.specular ({ SUM FOR_EACH_LIGHT : specular() * fresnelLight()} + fresnelFinal())

    + (1.0 - Kx) * FresnelTransmittance (
                       SurfaceNormal * ViewVector,
                       (1.0 - mat.specular),
                       mat.shininess
                   ) * mat.transmissionFilter * refraction()

    Kx does not exist (typo in spec. probably): probably is mat.specular, else is either mat.ambient OR mat.diffuse

  9. This illumination model is similar to illumination model 3 without ray tracing. The formula is:

    color = mat.ambient * ambientLight
    + mat.diffuse { SUM FOR_EACH_LIGHT : diffuse() }

    + mat.specular ({ SUM FOR_EACH_LIGHT : specular() } + reflection())

  10. This illumination model is similar to illumination model 4without ray tracing. The formula is:

    color = mat.ambient * ambientLight
    + mat.diffuse { SUM FOR_EACH_LIGHT : diffuse() }

    + mat.specular ({ SUM FOR_EACH_LIGHT : specular() } + reflection())

  11. This illumination model is used to cast shadows onto an invisible surface. This is most useful when compositing computer-generated imagery onto live action, since it allows shadows from rendered objects to be composited directly on top of video-grabbed images. The equation for computation of a shadowmatte is formulated as follows.

    color = Pixel color. The pixel color of a shadowmatte material is always black.

color = black

M = Matte channel value. This is the image channel which typically represents the opacity of the point on the surface. To store the shadow in the matte channel of the image, it is calculated as:

M = 1 - W / P

where:

P = Unweighted sum. This is the sum of all S values for each light:

P = S1 + S2 + S3 + .....

W = Weighted sum. This is the sum of all S values, each weighted by the visibility factor (Q) for the light:

W = (S1 * Q1) + (S2 * Q2) + .....

Q = Visibility factor. This is the amount of light from a particular light source that reaches the point to be shaded, after traveling through all shadow objects between the light and the point on the surface. Q = 0 means no light reached the point to be shaded; it was blocked by shadow objects, thus casting a shadow. Q = 1 means that nothing blocked the light, and no shadow was cast. 0 < Q < 1 means that the light was partially blocked by objects that were partially dissolved.

S = Summed brightness. This is the sum of the spectral sample intensities for a particular light. The samples are variable, but the default is 3:

S = samp1 + samp2 + samp3.

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