INTRODUCTION TO IMAGE
PROCESSING
Reading:
FK section 6(4) &
article from Sky
and Telescope: Sky on a Chip:
the Fabulous CCD
the ds9 image
processor
to load the first image, under File select Open then browse to the
path
C:\Program
Files\HOU-IP\images\Images-High
School\2browsers_guide_to_the_universe\browser5
As
you remember from class, a CCD image is basically a 3-dimensional array
of
numbers;
one dimension is the x-value of the pixel location: a second dimension
is the
y-value:
a third dimension is the number of photons (ok, really the electrons
produced
by the
incoming photons) that were counted in that pixel.
Where is the x,y
origin? (which
corner of the image?) How did you figure
it out?
Where on the screen is the photon count in each pixel recorded?
answer all underlined
questions;
non-underlined questions are optional
How to get rid of the
annoying green circles that pop
up when you (accidentally) click
somewhere in the image:
a) click on a green
circle (so that tiny squares
appear in the 4 corners);
then hit the delete button
OR
b) click on the Region
button in the topmost of the two rows of buttons
immediately above
the image; then click
on 'delall' in the second row of buttons to
delete all green
circles
Can you tell what type of
object it is?
What percentage of the image frame
would you say the object occupies?
how astronomers use the idea of 'false coloring' to bring out contrast
and
detail.
Experiment WHILE WATCHING: what happens to the color palette bar at the
bottom
and/or the Bias/Contrast parameters in the Colormap
Parameter window?
a)
to
get a taste of image processing
b)
to
learn something about some astronomical objects we'll encounter later
in the
course
Do you see any moons? How many?
How
many atmospheric bands can you see on the planet?
Can you find an appropriate Bias/Contrast combination that allows
you to see
all moons
AND the atmospheric bands? If
so, record the values.
Zooming out might help:
click on the Zoom
button in top row of buttons;
then click on the out
button in
the
second row
of buttons.
A number of pixel rows on the left side
of the image have been saturated (i.e., the
maximum number of electrons
possible on a pixel has been reached, and electrons
have spilled over
onto
adjacent rows of pixels; it is the equivalent to
overexposure on film.)
Measure the sun's diameter in
pixels. How did you do it?
What are the bright spots over the limb of the sun?
(use the sun
chapter
in your text)
what is the
name of the object?
exposure
time?
time
and date of exposure?
where
was the image taken? (hint:
look at the telescope name and the time)
What similar objects
to this are in the Stellar
Evolution summary?
(the Stellar
Evolution
Summary is accessible from the course page)
Notice the
white dwarf star at the very center.
Starting from the original image as loaded, how
many times must you
click on
zoom
in before you can start seeing the
individual pixels?
The
fireball in the upper
left
corner of the image was produced when a piece of
Comet Shoemaker-Levy
smashed
into Jupiter in 1994.
The known diameter
of Jupiter is 143,000 km.
Find the diameter of the
fireball;
show your work! remember the lab
guidelines
is the
fireball larger than Earth?
This remnant is one of the very few that contains a visible pulsar (or
neutron
star) at its
center. To find out which
of the central stars is the pulsar go to
figure 23-4
in Universe.
What operation(s) do you have to do to the image to make it match
exactly the
picture in
figure 23-4? There are a number of ways to manipulate images
found
under Edit and
under Zoom;
for
example, under Edit,
you can select
Rotate;
then under Zoom,
selecting 0,
90, 180, or 270 causes a
rotation of
those angles
RELATIVE TO THE
ORIGINAL IMAGE.
Are
the rotations produced clockwise or counterclockwise?
Flips are also possible: under Zoom: x, y, and xy
(again, always relative to the originally
loaded image.)
You might want to experiment a bit so that
you know what ds9 is calling
an x Flip;
you
might be surprised.
Tell me what
operations -- in what order --
you used to make the new browser image
exactly match the figure in Universe
23-4. (There is more than one correct
answer.)
1) Under Analysis, click
on Virtual
Observatory;
a
box should pop up showing several different image servers
2) click in the Chandra-Ed Archive
Server box; almost
immediately the
box should
turn
green, and a
browser window opens that lists images that
can be
loaded
The scale of the image is 0.5" (seconds of arc)/(Physical)
pixel.
Determine the diameter of Cas
A in pixels, seconds of arc,
and then light years.
The distance
to Cas A is
approximately
11,000 c-yrs.
You will need a large, labeled diagram to
accompany your
equations and
calculations of
the diameter in light years.
We believe that Cas
A
exploded in 1670.
How fast (on
average) have the outermost remnants been moving
(in km/s and as a
fraction of
the speed of light?)
what objects are you seeing in the
visible? what in
the x-ray? (see Universe fig 26-23)