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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.

Retrieving the Data

We 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.

Cleaning, Combining, 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 orientation.

Bringing the 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 and channels.

We create layers in a new document, where we can select the blend mode to screen and assign colors in a preferred order.

 

Editing in Adobe Photoshop

 

 

 

 

First 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 rotation.

Inprogress (Draft) Images

Early draft with diluted colors and saturated stars.

Later draft: The center of the nebula is still a bit saturated.

Outer nebulosity is improved. The orientation and cropping are not very favorable.

Making the Final Draft

The noisiness 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.

We also incorporate a non-polar image in a luminosity layer (with lowered opacity and a curves adjustment).

And 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.

"Cooler" Color Tones
"Warmer" Color Tones