Documentation Talk:Reference Section 5.1

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About Subsurface Light Transport, the following paper has sample values to use as reference for a few material:

--Maurice 13:28, 7 July 2010 (UTC)

  • added link to the documentation --jholsenback 14:47, 7 July 2010 (UTC)

Suggested change to ambient section below. Please check the links as I'm not sure what the commented linkto tags actually do.


The light you see in dark shadowed areas comes from diffuse reflection off of other objects. This light cannot be modeled directly using ray-tracing, however, the radiosity feature can do a realistic approximation at the cost of higher render times. For most scenes, especially in-door scenes, this is will greatly improve the end result.

The classic way to simulate ambient lighting in shadowed areas is to assume that light is scattered everywhere in the room equally, so the effect can simply be calculated by adding a small amount of light to each texture, whether or not a light is actually shining on that texture. This renders very fast, but has the disadvantage that shadowed areas look flat.

Note: Without radiosity, ambient light does not account for the color of surrounding objects. If you walk into a room that has red walls, floor and ceiling then your white clothing will look pink from the reflected light. POV-Ray's ambient shortcut does not account for this.

The ambient keyword controls the amount of ambient light used for each object. As the ambient light might be tinted, this is actually a color value, for example

finish { ambient rgb <0.3,0.1,0.1> } //a pink ambient

If all color components are equal, a single float value may be specified (e.g., 0.3 is treated as <0.3,0.3,0.3>). The default value is 0.1, which gives very little ambient light. As with light sources, physically meaningful values are greater than 0, but negative values actually work too, and the value may be abitrarily high to simulate bright light.

You may also specify the overall ambient light level used when calculating the ambient lighting of an object using the global ambient_light setting. The total light is given by Ambient = Finish_Ambient * Global_Ambient_Light_Source. See the section Ambient Light for details.

Ambient light affects both shadowed and non-shadowed areas, so if you turn up the ambient value, you may want to turn down the diffuse and reflection values. Giving high ambient to an object effectively gives it an intrinsic glow, however, if the intent is to actually have it glowing (as opposed to simulating background light), the emission keyword should be used instead. The difference is that actual glowing objects light up their surroundings in radiosity scenes (while ambient is then actually ignored).

Note: Specular reflected indirect illumination such as the flashlight shining in a mirror is not modelled by either ambient light or radiosity. For this, you need photons.

Froesccn 12:48, 8 October 2011 (UTC)

Phong Highlights

Something seems wrong in the following text (about placement of albedo, is it before or after phong ?):

The optional keyword albedo can be used right after phong to specify that the parameter is to be taken as the total diffuse/specular reflectance, rather than peak reflectance.

For example:

finish { albedo phong 0.9 phong_size 60 }

--Le Forgeron 14:57, 22 January 2012 (UTC)

  • oops ... it's been fixed --jholsenback 01:31, 24 January 2012 (UTC)