Guide

How-to: RAW processing of a star-spattered sky

3/8/2022

Fellow editor Jan Johannsen called me a «RAW wizard» in his article. However, there’s no magic involved in enhancing a night shot. In fact, it’s a matter of minutes.

Night shots can be massively enhanced after they’re taken – provided you took the photo in raw format and have RAW software such as Lightroom available. JPEG doesn’t allow making large changes.

As long as the file is available in RAW or the equivalent DNG, it can even be a photo taken from a smartphone. The example photo I chose was taken by Jan Johannsen with a Smartphone Sony Xperia 1 IV. What did I do with it? Well, after receiving the DNG file from Jan, I opened the image in Photoshop Lightroom. This is what it looked like.

This is what the image looked like when I first opened it in Lightroom or Photoshop.

White balance is key

The first thing I noticed about this photo is that white balance is off. White balance is the most important factor when it comes to colour. Jan’s smartphone camera automatically set the colour temperature to 7150 Kelvin, resulting in a brownish colour cast.

I reduced white balance massively, to about 3500 K. The lower the value, the bluer the sky appears. How blue you want the sky to look is up to you. However, at below 3000 K, the whole sky is blue and the pretty colour nuances disappear.

To see the effects of white balance better, I temporarily set dynamics and saturation to the maximum, i.e. +100. This is what the same photograph looked like after changing the colour temperature settings.

White balance at 2900 K: too cold and everything turns blue.

White balance at 3600 K: about right; the sky has rich colours.

Of course, I reduced dynamics and saturation again afterwards. I set them to about +30 for the time being.

Making stars more visible

Night skies are famously dark. So does the sky have to be set as dark as possible? No, because what’s key is the relative brightness. What does this mean? Well, the sky is brighter than the mountain range. I wanted to make this difference more visible through post-processing. The goal was to end up with a mountain range that appears as a black silhouette and in front of a much brighter sky.

I achieved this by raising the exposure and lowering the depths and black. There's no rule about how much to change these three settings – it depends on the photo and how you want it to end up looking. The difference between depth and black is that the black slider also darkens the dark parts of the sky, increasing contrast.

I couldn’t get the trees in the foreground to appear black even with the strongest darkening setting. They did bother me, though. In the photo in Jan's article, I tried to make them as inconspicuous as possible by reducing the yellow and green levels. But it would be better to mask them with the brush and lower the exposure a lot.

The finishing touches

With the most important adjustments done, what followed was refining the photo. This is what I did:

In the lower right area, I thought the sky looked a bit too green. Therefore, I changed the white balance and pushed the toning sliders a bit towards magenta. This also made the milky way stand out more clearly.
The sliders structure and clarity bring out the stars even more clearly, making even fainter celestial bodies easily visible. I only applied this to the sky to avoid noisy pixels in the foreground. The masking tool in Lightroom allows you to automatically select the sky.
Brightness, hue and luminance can also be adjusted per colour – in Lightroom under «HSL/Colour». I mainly adjusted the purple to emphasise the milky way even more.
Finally, I changed the brightness, white balance and saturation a bit. Since the settings influence each other, such a readjustment is almost always necessary. I ended up with a white balance of 3450 K.

What generally applies is that heavy processing leads to more noise. So don't overdo it and zoom in to one hundred percent every once in a while to inspect the noise. Once you zoom out and if you use a small version of the image, this noise disappears for the most part. So if I'm just using an image for Instagram or at a low resolution, I can go a little heavier than if I'm preparing a photo for 4K TV or a large print.

More processed, but with the risk of noise getting out of hand.

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David Lee

Senior Editor

David.Lee@digitecgalaxus.ch

My interest in IT and writing landed me in tech journalism early on (2000). I want to know how we can use technology without being used. Outside of the office, I’m a keen musician who makes up for lacking talent with excessive enthusiasm.