BBC Sky at Night - UK (2021-08)

Peter Ward lives in

Sydney, Australia. He

was the winner of the

APY 2020 ‘Stars and

Nebulae’ category

with ‘Cosmic Inferno’

August 2021 BBC Sky at Night Magazine 79

3 QUICK TIPS

1. Respect the GIGO principle
   (garbage in, garbage out), and don’t
   waste time by trying to recover
   detail from poor quality data.


2. Always calibrate your RAW image
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   data will be inaccurate and noisy.


3. Don’t be afraid to push the processing
   envelope, but always respect the
   intrinsic illumination of an object.

icon and you’re done (see Screenshot 1).

Once registered, the image data needs

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‘ImageIntegration’ window (see Screenshot

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previously registered image data. I use the

‘Median’ combine setting and ‘Winsorized

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shadow details without burning out the

highlights. To mimic a maelstrom of

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stars from the image data and show just

the nebulosity.

To do this I select the ‘StarNet’ function

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‘Apply’ button, saving the resulting

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The ‘StarNet’ star-removal routine is not

perfect and it leaves bright star halos and

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can be removed in Adobe Photoshop by

using ‘Patch’ or ‘Clone’ tools, as well as

applying Photoshop’s noise-reduction

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smooth out the nebulosity.

The last step in the process is to

“colourise” the image, or map a colour

palette to the grayscale image in

Photoshop. A new layer can be added by

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colours to map brightness changes within

the selected grayscale image (see

Screenshot 4). By moving the adjustment

sliders you can also vary the brightness

levels with different colour transitions.

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grayscale image, I found that using only

shades of red gave an unconvincing result.

However, I discovered there was no better

colour guide than in the actual news

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Photoshop’s colour selection tool, I

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orange tones from these images and

placed them into the gradient of the

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perfect (see main picture, opposite), and

gave something of an Earthly relevance to

the vast cosmic structures far beyond our

home planet.

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thermal noise (unwanted artefacts),
vignetting and the shadows from any
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noise-reducing algorithms.

Getting started
To start the registration process in
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bring up the ‘StarAlignment’ window (see
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the top right drop-down option and choose
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icon to the right of the ‘Output directory’
and select a folder to store the registered
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Þ Screenshot 1: The PixInsight
‘StarAlignment’ window is used for
registering the images...

Þ Screenshot 2: ...and the

‘ImageIntegration’ window is then used for

stacking the images

Þ Screenshot 3: Use the ‘StarNet’ function
to remove unwanted stars

Þ Screenshot 4: A colour palette is applied

to the grayscale image in Photoshop