A common technique to emphasize the three dimensionsionality of a two dimensional image is to use a depth-cueing effect, fading parts of the three dimensional scene into the background depending on how far they are from the observer. This is demonstrated below. Both pictures are directly from DINO. The one on the left fades into the black background, while the one on the right has equal intensity irrespective of the distance of the object from the observer.

With depth-cueing

No depth-cueing

This depth-cueing effect is implemented using fog, in the case above black fog. To achieve the same effect in POVray, light attenuation is used by adding the following to each .pov file (some numbers may vary depending on the scene):

// depth cueing
plane {z, 31.065
  texture {pigment {color rgbft <0,0,0,1,1>}}
  hollow interior {fade_power 2 fade_distance 18}
}

An infinite plane is defined along the xy-plane (normal pointing towards positive z, ie away from camera) positioned at a z value of - in this case - 31.065 (which is the position of the near clipping plane in DINO). The texture is set to a simple black and completely transparent surface - after all, we don't want to see the plane, but the objects behind it. This plane is also set to hollow, otherwise POVray would treat the area behind the plane as solid! Just think of the are behind the plane as 'inside'. The interior settings now finally specify how to treat the light behind the plane (from the POVray manual):

The fade_distance value determines the distance the light has to travel to reach half intensity while the fade_power value determines how fast the light will fall off. For realistic effects a fade power of 1 to 2 should be used. Default values for both keywords is 0.0 which turns this feature off.

The value for fade_distance is determined from the far clipping plane position in DINO. For the example from above, here are the rendered scenes with different settings:

no attenuation	fade_power 2.0 fade_distance 18
fade_power 2.0 fade_distance 12	fade_power 4.0 fade_distance 18

If you need to turn attenuation off, it is better to comment out the two lines specifiying the plane rather than setting the values to zero, because the scene will render much faster.

(c) 2001-2005 Ansgar Philippsen