Geology Reference
In-Depth Information
Figure 2.18. Mosaics combine more than one image to matching
pixels along frame boundaries and assigning average values to the
pixels, giving the appearance of a single image. (a) This set of
Mariner 10 images of the Caloris basin on Mercury was assembled by
hand; (b) the same scene as a computer-generated mosaic (courtesy
of the Jet Propulsion Laboratory).
Figure 2.17. Geometric projections involve shifting individual
pixels into new positions; for example, this image of Mercury was
taken at an oblique angle from the Mariner 10 spacecraft, viewed
off to the side (a), which was then orthographically reprojected
(b) so that the scale is near-uniform over the entire scene (as
though viewed
and the missing data can be applied. One must remember
that cosmetically improved images include DN values that
are not real (
Figs. 2.16
,
2.19
, and
2.20
).
“
straight-down
”
from the spacecraft; NASA
Mariner 10 FDS 27321).
2.8 Resolution
contrast. This overall process can be done automatically
or by hand.
Cosmetic processing. Awide variety of processes can
be applied to generate images that are more pleasing to the
eye. For example, individual pixels or blocks of pixels
might have DN
“
0
”
levels because parts of the detector
have been damaged, or because data were lost during
transmission from the spacecraft to Earth. The simplest
method of filling in the missing data is to use some
average value of the neighboring pixels for the missing
pixel. Similarly, blemishes, such as those caused by dust
grains, can be removed by reference to the calibration
les
The scale of individual pixels in a digital image and the
resolution of that image are somewhat related, but are
distinctive parameters that are often confused, even in
the planetary science community. Put simply, the scale
of a pixel is related to the dimension of the terrain pro-
jected onto the detector through the imaging system lens.
Thus, it is dependent primarily on the optics, the distance
of the camera from the terrain, and the size of each pixel of
the detector. The pixel scale then can be stated as some
length per pixel, such as 10 m per pixel, meaning that 10 m
