Rendering Depth Maps
Original Publication Date: 1998-Sep-01
Included in the Prior Art Database: 2005-Apr-04
Lipscomb, J: AUTHOR [+1]
Disclosed is a method to generate a computer generated image in which different colors represent different depth values. Such images are commonly referred to as depth maps.
Rendering Depth Maps
Disclosed is a
method to generate a computer generated
image in which different colors represent different depth values.
Such images are commonly referred to as depth maps.
Depth maps are
2-dimensional pixel arrays where every pixel
has associated with it a depth value. The depth value represents
the distance of the pixel from the viewer or some other point in
space. Several applications require the availability of depth maps.
Such applications are for instance color stereo, z-buffering or
light-buffers. The generation of depth maps is commonly part of the
rendering process in the traditional polygon rasterization process.
The resulting depth map is stored in memory area known as the
z-buffer. The z-buffer is used to resolve visibility and remove
hidden surfaces from the display. However, some rendering system use
alternate methods to determine visible objects and hence do not
construct z-buffer information. Furthermore, some rendering systems
construct z-buffer information but do not provide applications with a
mechanism to access this information. It is therefore the object of
this disclosure to describe a method to generate depth maps in
systems that do not provide z-buffers. The methods described in
more detail below use depth-cueing and projective texture mapping to
color surface points of the model according to their distance from a
given point in space. The depth resolution of this method is
directly proportional to the number of colors the rendering system
The basic idea
is to generate an image in the frame buffer
of the graphics system in which different colors represent different
depth values. This image can then be retrieved from the frame buffer
and used as a depth map. Fig. 1 shows an arrangement of objects and
the associated depth-map. (For simplicity a 2-dimensional projection
of the scene is shown.)
depth map can be interpreted as mapping
values of a weakly monotonic function onto all points in the scene.
Monotonicity will ensure that any two points at different distances
from the viewer will be assigned different values. Figure 2 shows an
example of this mapping.
graphics systems offer two features that can be
used to implement the mapping step just described: depth cueing and
projective texture mapping. The generation of depth maps using
these two mechanism is described below.
Cueing. Depth cueing (also known as
the intrinsic color Ci of a point with a second, pre-defined color
Cf. The second color is referred to as the fog color. The
contributions of intrinsic color and fog color depend on the fog
factor f which ranges from 0 to 1. The fog factor f is derived from
the depth value z of a surface point by linearly interpolation...