Image Processing Reference
In-Depth Information
the device used. For example, for cross-sectional images generated by the med-
ical imaging devices such as X-ray CT or magnetic resonance imaging (MRI),
factors such as the capabilities of the imaging devices and the meaning of the
data obtained, as well as the burden placed upon the patient, must be taken
into consideration. Recent X-ray CT devices allow for the reconstruction of
cross sections at an arbitrary cross-sectional spacing (reconstruction pitch)
after acquisition of the sensing data.
On the other hand, in the case of microscopic imaging of pathological sam-
ples, digitalization is sometimes performed by creating a continuous image (a
micrograph) from scans of cross sections after exposure by sequential shaving
of the specimen. In such a case, the spacing of cross sections is determined
at the point where the photograph is taken or the specimen is shaved, but
selection of the sampling distances within the cross section is limited only by
the capabilities of the scanner, leaving a wide degree of freedom.
1.2 What does “3D image” mean?
The terms “3D image” and “3D image processing” are generally used with a
wide variety of meanings. This section and the one following it give a simple
overview of those meanings.
1.2.1 Dimensionality of the media and of the subject
It is first necessary to make a clear distinction between the dimensionality of
the media (or, the dimensionality of the data structure ) and that of the subject
(or content ).
The former refers to the dimensionality of the space (media) that con-
tains the record of the image. When density values for each point in an n -
dimensional space are recorded, the result is referred to as an n -dimensional
image. For example, an image drawn on a 2D plane such as paper is a 2D im-
age, and an image recorded in a 3D space is a 3D image. For an n -dimensional
digital image, density values are recorded in an n -dimensional array.
Dimensionality of the subject refers to the dimensionality of that thing
( scene ) that is recorded in the image, or to that object that is the main
subject of processing . For example, an image that records a 3D scene or a 3D
object might be called a 3D image, even if it is recorded on paper. Similarly,
a 3-dimensional scene drawn using computer graphics is referred to as 3D
graphics, even when displayed on a 2D screen.
1.2.2 Types of 3D images
The meaning of the word “dimension” discussed above is used with a variety
of meanings. The following are differing types of what each are called 3D
images:
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