INTRODUCTION - Fundamentals of Three-Dimensional Digital Image Processing - page 4

(1) Image data that are recorded (stored) in a 3D array : This is a 3D image (a
continuous image, or a digital image) of the type described in Section 1.1,
and the main type discussed in this topic. Specific examples are given in
the following section and subsequently throughout the topic, starting in
Chapter 2. More specifically, however, this topic is most concerned with
3D images in which recorded data are related not only to visible surfaces,
but also to structures internal to the subject.
(2) Images depicting 3D scenes and 3D objects : In this case, the term 3D
image is used despite the fact that it is a picture, photograph, or graph
drawn on a 2D space (paper, etc.). In actuality, however, we will limit this
to those images in which steps have been taken so that the image will be
recognized by the viewer as that of a 3D scene or object.
(3) Images intentionally created so as to create a stereoscopic effect ( asense
of 3 -dimensionality ) in the viewer : This would refer to, for example, a pair
of 2D images intended to be viewed with one eye each (a stereogram). The
image described in Remark 1.3 falls into this category.
(4) Images in which the density value itself contains information related to a
3D space : For example, range images and certain types of relief contour
maps (see Remark 1.4).
(5) Special images in which the form of a 3D object is recreated optically :This
would include various types of holograms.
(6) 2D dynamic images : This refers to a time series of 2D images that record
changes over time (movement of an object, etc.) in the subject scene.
These images are also recorded in a 3D array, but the coordinate axes are
spatiotemporal, measuring 2D positioning in space along with time, and
so in that sense are not truly isotropic. An extension of this type would be
a 4D image that records the changes over time of a 3D image as described
in (1) (in other words, a 3D movie).
Of the above, only images of the type described in (1) contain information
related to the overall structure of a 3D object, including its interior. In this
topic, when it is necessary to make a distinction with other types, such images
will sometimes be called true 3D images or voxel construction images .
Remark 1.3. There exist a variety of different ways to create images that
cause a feeling of reality or immersion in the viewer of a 3D space. Projection of
images onto extremely large, curved screens or domed screens is one example.
Such methods cause the viewer to visually interpret themselves as being inside
of a surrounding 3D environment. Of course, actual objects are not recreated,
and so only those faces shown in the picture can be seen. The viewer could
not move so as to see the opposite side of an object, for example.
Aside from this, there are methods by which an image is created so
that the same light rays or wave fronts as when viewing the actual object
are visualized by the observer. Examples are holograms and volumegraphs
[Dohi00, Nakajima00]. These examples allow viewers to change, to some ex-
tent, the visible face of an object by changing their point of view.