Geology Reference
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Figure 2.18. (cont.)
on the ground is registered as a single DN value by the
pixel detector.
Resolution is a much more complicated parameter than
pixel scale, since it refers to the smallest object that can be
identi ed in the image. Thus, the contrast of the object in
relation to its background, the shape of the object, the
responsitivity of the particular detector to the composition
and surface texture, and other factors all play a role in
resolution, as well as the size of the object in relation to the
pixel scale. For example, a stark white object ten times
larger than the pixel scale might not be seen on an image if
the object were placed on a pristine snow field, while
some linear features, such as fault traces, might be
detected even though the width of the fault might be
smaller than the pixel scale, simply because of its shape
and the contrast with the surrounding terrain.
Because of the complications in de ning resolution,
digital images are often (erroneously) stated to have a
Figure 2.19. Various cosmetic image processing techniques remove
artifacts such as
donuts
( Fig. 2.16 ),
filling-in pixels or lines of pixels
during electronic data transmission (a) by assigning
average values of surrounding pixels to the dropped pixels, and by
removing reseau (
dropped
registration marks built into the imaging
system used for precise location of surface features) to produce a
r,
final image (b).
object, depending on the object ' s shape. To further com-
plicate the issue, some images will be stated to have a
resolution of x meters per line pair of pixels, which is an
attempt to take into account the need for more than one
pixel for object detection.
of x meters per pixel, when this phrase
actually refers to the pixel scale or angular resolution.
Obviously, it takes more than one pixel to discern an
resolution
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