Documentation Talk:Reference Section 5.1
About Subsurface Light Transport, the following paper has sample values to use as reference for a few material:
http://graphics.stanford.edu/papers/bssrdf/bssrdf.pdf
--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.
Ambient
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.
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.
The ambient keyword controls the amount of ambient light used for this object. As the ambient light might
be tinted, this is actually a color value, however, a single float value of, e.g., 0.3, gets promoted to the full color vector <0.3,0.3,0.3,0.3,0.3>, which is acceptable because only the red, green and blue parts are used.
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. 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.
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.
You can set the ambient for each object separately in its finish statement, for example
finish { ambient rgb <0.3,0.1,0.1> } //a pink ambient
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.
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)