Since objects in POV-Ray are illuminated by light sources, the portions of those objects that are in shadow would be completely black were it not for the first two finish properties, ambient and diffuse . Ambient is used to simulate the light that is scattered around the scene that does not come directly from a light source. Diffuse determines how much of the light that is seen comes directly from a light source. These two keywords work together to control the simulation of ambient light. Let's use our gray sphere to demonstrate this. Let's also change our plane back to its original green and white checkered pattern.
plane {y,-1.5
pigment {checker Green, White}
}
sphere { <0,0,0>, 1
pigment {Gray75}
finish {
ambient .2
diffuse .6
}
In the above example, the default values for ambient and diffuse are used. Render this to see what the effect is and then make the following change to the finish.
ambient 0
diffuse 0
The sphere is black because we have specified that none of the light coming from any light source will be reflected by the sphere. Let's change diffuse back to the default of 0.6.
Now we see the gray surface color where the light from the light source falls directly on the sphere but the shaded side is still absolutely black. Now let's change diffuse to 0.3 and ambient to 0.3.
The sphere now looks almost flat. This is because we have specified a fairly high degree of ambient light and only a low amount of the light coming from the light source is diffusely reflected towards the camera. The default values of ambient and diffuse are pretty good averages and a good starting point. In most cases, an ambient value of 0.1 ... 0.2 is sufficient and a diffuse value of 0.5 ... 0.7 will usually do the job. There are a couple of exceptions. If you have a completely transparent surface with high refractive and/or reflective values, low values of both ambient and diffuse may be best. Here is an example.
sphere { <0,0,0>, 1
pigment { White filter 1 }
finish {
ambient 0
diffuse 0
reflection .25
refraction 1
ior 1.33
specular 1
roughness .001
}
}
}
This is glass, obviously. Glass is a material that takes nearly all of its appearance from its surroundings. Very little of the surface is seen because it transmits or reflects practically all of the light that shines on it. See glass.inc for some other examples.
If you ever need an object to be completely illuminated independently of the lighting situation in a given scene, you can do this artificially by specifying an ambient value of 1 and a diffuse value of 0. This will eliminate all shading and simply give the object its fullest and brightest color value at all points. This is good for simulating objects that emit light like lightbulbs, and for skies in scenes where the sky may not be adequately lit by any other means.
Let's try this with our sphere now.
sphere { <0,0,0>, 1
pigment { White }
finish {
ambient 1
diffuse 0
}
}
}
Rendering this we get a blinding white sphere with no visible highlights or shaded parts. It would make a pretty good streetlight.
In the glass example above, we noticed that there were bright little hotspots on the surface. This gave the sphere a hard, shiny appearance. POV-Ray gives you two ways to specify surface specular highlights. The first is called Phong highlighting . Usually, Phong highlights are described using two keywords: phong and phong_size . The float that follows phong determines the brightness of the highlight while the float following phong_size determines its size. Let's try this.
sphere { <0,0,0>, 1
pigment { Gray50 }
finish {
ambient .2
diffuse .6
phong .75
phong_size 25
}
}
Rendering this we see a fairly broad, soft highlight that gives the sphere a kind of plastic appearance. Now let's change phong_size to 150. This makes a much smaller highlight which gives the sphere the appearance of being much harder and shinier.
There is another kind of highlight that is calculated by a different means called specular highlighting . It is specified using the keyword specular and operates in conjunction with another keyword called roughness . These two keywords work together in much the same way as phong and phong_size to create highlights that alter the apparent shininess of the surface. Let's try using specular in our sphere.
sphere { <0,0,0>, 1
pigment { Gray50 }
finish {
ambient .2
diffuse .6
specular .75
roughness .1
}
}
}
Looking at th result we see a broad, soft highlight similar to what we had when we used phong_size of 25. Change roughness to .001 and render again. Now we see a small, tight highlight similar to what we had when we used phong_size of 150. Generally speaking, specular is slightly more accurate and therefore slightly more realistic than phong but you should try both methods when designing a texture. There are even times when both phong and specular may be used on a finish.
There is another surface parameter that goes hand in hand with highlights, reflection . Surfaces that are very shiny usually have a degree of reflection to them. Let's take a look at an example.
sphere { <0,0,0>, 1
pigment { Gray50 }
finish {
ambient .2
diffuse .6
specular .75
roughness .001
reflection .5
}
}
}
We see that our sphere now reflects the green and white checkered plane and the black background but the gray color of the sphere seems out of place. This is another time when a lower diffuse value is needed. Generally, the higher reflection is the lower diffuse should be. Try lowering the diffuse value to 0.3 and the ambient value to 0.1 and render again. That is much better. Let's make our sphere as shiny as a polished gold ball bearing.
sphere { <0,0,0>, 1
pigment { BrightGold }
finish {
ambient .1
diffuse .1
specular 1
roughness .001
reflection .75
}
}
}
That is very close but there is something wrong with the highlight. To make the surface appear more like metal the keyword metallic is used. Add it now to see the difference.
sphere { <0,0,0>, 1
pigment { BrightGold }
finish {
ambient .1
diffuse .1
specular 1
roughness .001
reflection .75
metallic
}
}
}
We see that the highlight has taken on the color of the surface rather than the light source. This gives the surface a more metallic appearance.
The degree of refraction, i. e. the amount of bending that occurs, is given by the keyword ior , short for index of refraction . If you know the index of refraction of the substance you are trying to create, you may just use that. For instance, water is 1.33, glass is around 1.45 and diamond is 1.75. Let's return to the example of a glass sphere we used earlier.
Render this again and notice how the plane that is visible through the sphere is distorted and turned upside-down. This is because the light passing through the sphere is being bent or refracted to the degree specified. Try reducing ior to 1.25. Try increasing it to 1.75. Notice how the distortion changes.
Transparent objects can be made to cause the intensity of light passing through them to be reduced. In reality, this is due to impurities in scattering the light. Two float values determine the effect: fade_distance is the distance the light has to travel to reach one-half its original intensity and fade_power is the degree of falloff. Let's try an example of this.
sphere { <0,0,0>, 1
pigment { White filter 1 }
finish {
ambient .1
diffuse .1
reflection .15
refraction 1
ior 1.45
specular 1
roughness .001
fade_distance 5
fade_power 1
}
}
This gives the sphere a slightly clouded look as if not all of the light was able to pass through it. For interesting variations of this texture, try lowering ior to 1.15 and raising reflection to 0.5.
One thing we do notice is that the shadow of the sphere is still the same old flat gray shadow we have had all along. If there is all this light refraction going on shouldn't there be something going on with the shadow as well? That something would be due to an effect known as caustics . POV-Ray cannot do caustics but it can fake them to some degree. This is an easy one. Simply add caustics 1 to the finish block and re-render to see the effect. What we see is a highlight in the shadow that simulates the effect of light passing through the sphere and being focused because of the curved surface. Remember that this is not real caustics, so changing other finish parameters like ior will not affect the caustic highlight. The faked caustic is limited to the area shadowed by the corresponding object.
Halos are a texture feature allowing you to fill the interior of an object with particles. The distribution of these particles can be modified using several density mappings and density functions. The particles can emit light to give fire- or laser-like effects or they can absorb light to create clouds or fog.
A halo is attached to an object, the so called container object, just like a pigment, normal or finish. This object is completely filled by the halo but you won't see anything if you do not make sure that the object is hollow and the surface is translucent. How this is accomplished will be shown in the next section.
When working with halos you always have to keep in mind that the container object has to be hollow and translucent.
