To compare bands or to compare image bands before and after an operation, the
images can be displayed in different windows, visible on the screen at the same time.
The relationship between gray shades and pixel values can also be detected.
The pixel location in an image (rows and columns), can be linked to a georeference
which in turn is linked to a coordinate system which can have a defined map projection.
In this case, the coordinates of each pixel in the window are displayed if one
points to it.
The objectives of the exercises in this section are:
- to understand the relationship between the digital numbers of satellite images and
the display, and
- to be able to display several images, scroll through and zoom in/out on the images
and retrieve the digital numbers of the displayed images.
Satellite or airborne digital image data is composed of a two-dimensional array of
discrete picture elements or pixels. The intensity of each pixel corresponds to the
average brightness, or radiance, measured electronically over the ground area corresponding
to each pixel.