Creating the BoomerangNebula
Press Release Image
by Lisseth Gavilán
The Boomerang is a reflection
nebula taken with the Advanced Camera
(ACS) for polarimetry calibrations of
instruments onboard the Hubble Space Telescope.
The following describes the step-by-step
procedure involved in taking raw telescope
data and creating a press release image.
retrieved all Boomerang data from the
Hubble Space Telescope archive. We had
73 datasets to choose from. Several images
were taken with different instruments
onboard Hubble. We chose to only work
with the ACS Wide Field Camera (WFC) data.
and Aligning the Data
After bringing the complete
datasets from the Hubble archive to a
UNIX machine we take care of cosmic rays,
multiple pointings, and rotations of like
filter data by using a PyRAF Multidrizzle
routine. Images of the same filter are
now combined. Cosmic rays that only appear
in one image but not in another are removed
by this combining process. Multidrizzle
also provides automated detection, flagging
and removal of residual cosmic rays. The
end result is a series of single filter
images that are all aligned to the same
Data into Adobe Photoshop via FITS Liberator
FITS liberator is a Photoshop
plug-in that allows us to edit astronomical
images (which come in the standard FITS
format.) It provides black and white levels
histograms, clipping values, image transforms.
In Adobe Photoshop we can
work with scaled images, masks, layers
We create layers in a new
document, where we can select the blend
mode to screen and assign colors in a
in Adobe Photoshop
we assign RGB colors to each filter (in
this case to each polarizer from the F606W
filter). These colors usually corresponding
to the filter wavelengths for realism.
However, exaggerated colors may be used
to accentuate features. Many adjustments
are made, including intensity, contrast
and color level. The final touch-ups include
bad pixels, bleeding, cheap seams and
draft with diluted colors and saturated
draft: The center of the nebula
is still a bit saturated.
is improved. The orientation and
cropping are not very favorable.
the Final Draft
in the fainter parts has been reduced,
and the star colors have been neutralized.
We brought the intensity of the brightest
pixel to pure white, and brought the background
to pure black.
also incorporate a non-polar image in
a luminosity layer (with lowered opacity
and a curves adjustment).
the final results are: More detail visible
close to the central star. The contrast
enhanced in the inner, brighter as well
as the outer, fainter structures.