How to edit aurora astrophotos

Insight Investment Astronomy Photographer of the Year 2015 Aurora winner Jamen Percy reveals the secrets of post-processing shots of the Northern Lights.

Jame Percy's image of aurora, which won the Aurora category at Insight Astronomy Photographer of the Year 2015. Credit: Jamen Percy

My IAPY 2015-winning aurora image ‘Silk Skies’ was taken in only four seconds, but took eight years of practice to get right. Only a small amount of post-production was actually applied to the image – but the adjustments that I made were essential and I apply them to all my aurora images.

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My adjustments are made in the RAW format in Adobe Lightroom. I always start with Lens Corrections.

To do this, click on the Develop tab and scroll down to Lens Corrections, then click Enable Profile Corrections.

This is great because it has all of the lens’s discrepancies built-in, so it counters vignetting and distortion perfectly according to the lens used.

Þ Jamen’s shot straight from the camera – a foreground is useful for balancing colour later on. Credit: Jamen Percy
Jamen’s shot straight from the camera – a foreground is useful for balancing colour later on. Credit: Jamen Percy

After that click the Colour tab inside the Lens Corrections module and then the Remove Chromatic Aberration box.

This is really important for aurora photographs as there is often a bad red/blue fringing around contrasted edges, particularly the stars.

Chromatic aberration varies in severity between lenses and the f/stop used.

If you stop your lens down it will usually reduce it, but of course you can’t with aurora photography, as you need as much light as you can entering the lens.

This is why I always stick to high-quality lenses.

Jamen's aurora image before Lens Corrections have been applied. Credit: Jamen Percy.
Jamen’s aurora image before Lens Corrections have been applied. Credit: Jamen Percy.
Jamen's aurora image after Lens Corrections have been applied. Credit: Jamen Percy.
Jamen’s aurora image after Lens Corrections have been applied. Credit: Jamen Percy.

Next I adjust the detail. For aurora photos I slightly increase the sharpness.

Most DSLRs by default shoot a little soft, but this is intended – it is anticipated that you adjust your own sharpening in post processing.

I do this just to bring out the stars and any foreground detail. It will have no effect on the soft shapes of the aurora.

In addition I add noise reduction – not a lot, but just enough to smooth some of that harsh grain.

Stars offer suffer chromatic aberration in aurora pics – fixing this is vital. Credit: Jamen Percy
Stars offer suffer chromatic aberration in aurora pics – fixing this is vital. Credit: Jamen Percy

The finer points

Once the core corrections are done I tweak up the exposure to get the perfect brightness, ramp up the contrast to make the image really pop and raise the clarity a small amount.

This enhances the mid-tone detail, which often includes auroral beams.

I never raise the saturation; if anything I would bring it down as altering the contrast tends to fire up the colours enough.

If you increase the saturation too much, the image becomes ‘overcooked’ and can look fake.

It’s a common error and something to avoid. As a nature photographer – which as an astro imager, you are – you should always represent the natural world accurately.

The final tweak I make is the white balance, which can be tricky. It is imperative that you represent the true colours as you saw them or you risk being discredited.

Jamen's aurora image before Noise Reduction has been applied. Credit: Jamen Percy.
Jamen’s aurora image before Noise Reduction has been applied. Credit: Jamen Percy.
Jamen's aurora image after Noise Reduction has been applied. Credit: Jamen Percy.
Jamen’s aurora image after Noise Reduction has been applied. Credit: Jamen Percy.

It’s good to have foreground objects in your picture as you (and the viewer) can use these as a colour reference.

Getting the correct white balance can only be done by memory and by eye, which is why I try to process my aurora images as soon as I get back to base, as the colours are still shimmering fresh in my mind.

If you are struggling to find the correct white balance, a good starting point is to use the White Balance Eye Dropper tool.

First click on the tool (it is in the right panel of Develop tab) then click on part of the scene that is white and influenced by the light of the aurora.

The image will usually go too warm. Roll in a little bit more blue with the slider above the eye dropper, then a bit of green and I find in most occasions this is close to what the moment was.

This will always vary with the colour of the aurora, any light pollution or lunar glare, so there is no set-in-stone white balance setting.

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This article originally appeared in the September 2016 issue of BBC Sky at Night Magazine. Jamen Percy’s ‘Silk Skies’ image won the Insight Astronomy Photographer of the Year 2015 aurora category.