Image Display Orientation
Display orientation refers to whether row number
increases upward or downward. The orientation also affects the
sense in which
angles are measured. This is important to know
because, as described below, images in different formats are
displayed in different directions.
Definitions
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FITS format images are displayed displayed with
the origin (first pixel) in the lower left corner. This is
the convention used in all scientific software applications that
support FITS format. You can also
reverse the display direction to accommodate
unconventional FITS images.
-
Other formats, including TIFF, BMP, and JPEG do
not specify the display orientation. Mira follows the tradition of
displaying these graphics formats with the origin (first pixel) in
the upper left corner.
Comments
Since the orientations are different between FITS
and the other formats, a FITS image and, for example, a TIFF image
of the same field of view, will be displayed differently. To appear
with the same orientation on the screen, row number will increase
upward in the FITS image but will increase downward in the TIFF
image. Suppose we have an image that is 1000 x 1000 pixels both in
FITS format and in TIFF format. The different orientations means
that a pixel at coordinate (500,100) in the FITS image will be at
coordinate (500,900) in the TIFF image.
Because of the orientation differences, if a FITS
image appears upside down, then at some time in its past history it
was not saved with normal orientation of a FITS format image.
Related Topics
Image Coordinate System
FITS Image Orientation
Pixel Coordinate Definition
Sub Pixel Coordinate Definition
World Coordinate System
Angle Measurement Definition
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