Image Formation & Display
Images are a description of how a parameter varies over a surface.
For example, standard visual
images result from light intensity variations across a two-dimensional plane.
However, light is
not the only parameter used in scientific imaging.
For example, an image can be formed of the
of an integrated circuit,
in a patient's artery,
during an earthquake, etc.
These exotic images are usually
converted into conventional pictures (i.e., light images), so that they can be evaluated by the
This first chapter on image processing describes how digital images are formed and
presented to human observers.
Digital Image Structure
Figure 23-1 illustrates the structure of a digital image.
This example image is
of the planet Venus, acquired by microwave radar from an orbiting space
Microwave imaging is necessary because the dense atmosphere blocks
visible light, making standard photography impossible.
The image shown is
represented by 40,000 samples arranged in a two-dimensional array of 200
columns by 200 rows.
Just as with one-dimensional signals, these rows and
columns can be numbered 0 through 199, or 1 through 200.
In imaging jargon,
each sample is called a
, a contraction of the phrase:
in this example is a single number between 0 and 255.
image was acquired, this number related to the amount of microwave energy
being reflected from the corresponding location on the planet's surface.
display this as a
, the value of each pixel is converted into a
, where 0 is black, 255 is white, and the intermediate values are
shades of gray.
Images have their information encoded in the
, the image
equivalent of the time domain.
In other words, features in images are
This means that the spacing and
number of pixels are determined by how small of features need to be seen,