I hate to tell you this, but almost ever Milky Way shot you see uploaded has probably been Photoshopped/processed in some way. Post-processing is as much a part of astrophotography as taking the shot is. The two go hand in hand; however, there are an abundance of blogs out there on how to shoot Milky Way shots (such as this one from Lonely Speck), but relatively few on how to actually convert what you’ve captured on your sensor into those beautiful images you see other people uploading. So, this is my attempt to show you how I processed one of my photos. I’m using Lightroom 5.5 for all of my processing, but use whatever photo editing program you like – I’ll go through all the steps I used and why I make the decisions I do. HOWEVER, these are my choices and not yours – the best way to understand processing is to do it yourself, so that’s where we’ll start…
First up, if you’re not shooting in RAW then you need to start. There are some commentators emerging who are saying jpgs are more useful than RAW files, but the reality is, if you’re not shooting in RAW you won’t be able to do half the stuff I talk about here. Astrophotograph means RAW. But, maybe you don’t have a DSLR or you live in a light polluted area or, you just can’t be bothered standing in a freezing river in the middle of the night to take a selfie. To help you out, I’ve included the RAW file (in DNG format) here for you to play with. I took this photo last night on my Sony A7ii with a Samyang 14mm f/2.8 lens. It was a single image shot at 14mm, f/2.8, 25 second exposure and ISO3200. Download the file and play with it. Muck around with it – it is yours under the creative commons license. I’d love to see how you interpret the same raw image, so post it back here as a comment or post it on my Facebook page – remember, YOU make the choices to come up with the result you want to see – you’re the artist now.
Start at the Very End
It seems odd, I know, but always start with what you want the image to look like in your mind. What colours/feel/emotion do you want your image to show? Imagine that final image and then work towards that goal. You may adjust that ideal image while your process, but you need a goal to aim for. For me, I wanted a clean blue/purple feel with a punchy Milky Way in the middle. Here’s a comparison between the original image and the final processed shot that I was aiming for.
Once I’ve downloaded the images onto the computer and found a picture I want to process I always start by correcting the lens distortion. The automatic lens correction is always a good place to start, but you may still have to do some manual adjustments to eliminate the distortion from your lens. Of course, the amount of distortion depends on the lens you’re using – I shot this with a Samyang 14mm f/2.8 lens, so the lens correction makes a big difference to the edges of the image.
Cropping and Composition
I’ll admit, I made a mistake with this shot and didn’t make sure the gear was completely level before shooting – happens when you’re in a flowing river in the middle of the night, but a good chance to practice some cropping. I crop not only to straighten an image, but also to get the composition I want. So, adjust the image to suit your needs and focus in on the elements that suit you. Lightroom has a handy ruler tool that helps with leveling out a shot – you can draw the ruler across a flat horizon and it’ll adjust the image accordingly. I also used cropping as an opportunity to keep the river I was standing in as part of the bottom third and the stars to occupy the upper two thirds.
I always tend to start with adjusting the white balance. For me, white balance has such a substantive effect on the whole feel of an image that it’s the first thing I adjust and build the rest of the processing around it. Doesn’t mean I can’t go back and adjust the white balance later, but it’s the first step. I always like to see what Lightroom thinks the WB should be by doing ‘Auto’ white balance. Sometimes I like it, sometimes I don’t. In this case, I wanted something with a more blue feel than what Lightroom suggested, so adjusted the colours to suit my taste.
Time to get Sliding
Now, we start to get into the guts of post processing and where you really see the advantage of using RAW files. Without a RAW file you wouldn’t be able to get the fine adjustments from the various tone sliders available in most post processing software programs. I wish there was a hard and fast rule to say what you MUST do with the sliders, but there really isn’t. I started by sliding each slider to the maximums to see what they did and then found a balance that I liked. I personally don’t like the full on, highly sharpened and contrasted Milky Way shots – I prefer the flatter, more subtle shots, so I only adjusted the sliders a little. Here are the final choices I made for the tones.
Embrace your Curves
The Tone Curve is another way to get some real expression in your shots. As a basic overview, the top right controls the highlights and brighter tones while bottom left is for the darker tones. I’m really focusing on getting the stars to punch out with the tone curve, so I have gone with an S-shape curve. This means the highlights (such as stars) stand out as brighter while the darker tones (like space) are made darker, given you greater contrast between the two. As I said earlier, I prefer a slightly subtler effect, but the more aggressive you are with your S-shape tone curve the greater the contrast.
Noise is all those flecks and discolouration that comes with shooting in dark conditions and with a high ISO. The higher the ISO, the lighter your image; BUT, as a result, you get noisier pictures. Noise is the bane of astrophotographers, especially those who can’t afford high quality glass or some of the hardcore camera bodies out there. I have a good, mid-range Full Frame camera in a Sony A7ii, so it handles noise pretty well, but I still like to eliminate as much as I can. The noise reduction tool in Lightroom is ‘ok’ but it does tend to smooth everything out a little too much, so I only use it sparingly. There are heaps of ways to reduce noise, such as image stacking, but for the purposes of this shot where multiple images wasn’t possible, I’ll just use the slider. There are two areas I like to focus on for noise reduction – what effect does the noise reduction slider have on the foreground (which I want to be nice and sharp) and what effect does it have on the stars (after all, that’s what I want to be the hero of the pic!). I settled on about 25% for noise reduction. You can see that the noise reduction does soften the image, so you can do some sharpening after the fact, if you want, but I’ll leave that alone for now.
I spotted something in the shot that I hadn’t seen with the naked eye (or even seen on the camera until I started processing the shot) and that’s a faint whisp of green on the horizon. There was no real aurora activity that night (KP3) so it could be airglow or just the very faintest fleck of aurora. Anyway, I liked it and I want to see more of it. Lightroom gives you the option to selective adjust the hue, saturation and luminescence of each colour in the shot. Rather than making the WHOLE shot green, I just increased the saturation of the green tones in the image (which, in this shot, is only that space snot on the right, so nothing else is disturbed).
I also want to give the shot a little more purple in the Milky Way without making the rest of the shot purple, too (which would be the case if you adjusted the white balance to add more magenta). When we know the stars are primarily the brighter elements in the shot you can selectively colour these with the ‘Split Toning’ tool. I chose a soft violet colour and added a touch of saturation. If you want more colour, then up the saturation and adjust slowly to get the feel you want. Equally, if you want to change the colour of the darker tones, you can do that with split toning – I tried that, but didn’t like the results so left that blank.
The Gradient Tool
The gradient tool is really good for getting smooth transitions in your processing. I’m not going to use it for much, but there is one area I need to fix up. The Sony A7ii sensor tends to give you this purpley tinge to the edges when shooting in low light. Wasn’t too much of an issue in the original shot BUT now I’ve added more puple into the shot and increased the exposure a bit in the tone adjustments this distortion is standing out too much for my liking. The way I’ve corrected this is by using gradient tool to desaturate the bottom of the picture and then slowly grade into normal saturation for the rest of the picture. By the time the Milky Way kicks in, we’re back to full saturation.
So, this is where I start to wonder how far I should go with the processing. I really, really don’t like manually painting an image because it feels too fake. However, it is a common technique and I’m here to show you what’s available. Let’s start by using the brush tool on the stars. The whole image is looking a little ‘flat’ to me. I want it to punch more, so I’m using the brush tool to add more oomph to the stars by increasing the highlights more, upping the clarity and saturation and decreasing the exposure (to help the stars stand out from the dark background). I manually paint the entire starscape. Let’s see how it looks…
Hmmm, it’s ok, but now the Milky Way feels a little washed out. So let’s use the brush tool to selectively enhance that central strip of stars. I try to make it punch by dropping the exposure of the Milky Way some more and also increasing the contrast. I also adjust the temperature and tint to give the Milky Way a little more selective colour. BUT, how do you do this without it looking garish? Well, this is how I do it. Start by using a large brush tool and making a straight line down the Milky Way – yeah, it looks awful! That’s ok, we’ll fix it up. Hold down alt and the brush tool changes from having a plus (+) sign to a minus (-) sign. Use a really large soft brush (Feather=100) and slowly dip into the Milky Way to soften the whole selection. I bounce my cursor all along the Milky Way to ‘dig’ away at what I initially selected. If you turn on the ‘Show Selected Mask Overlay’ you’ll be able to see what you are influencing with your brush tool – by using a soft brush to slowly inch away at an image you get a much more subtle selection and it doesn’t look as obvious as doing a big manual brush down the middle. Using a soft brush to eat away at your selection also means you’re able to get that blend between the Milky Way and the rest of the background stars. If the difference is too harsh when you turn off the mask then carry on slowly eating away at your mark with the anti-brush tool.
After we’ve played with the brush tool on the stars and the Milky Way we can see the difference it has made to the picture. Again, the more you do, the more aggressive the look, but that’s not what I had in mind, so I’ve tried to avoid that.
Final bit of brushing is for the river. It looks a little bland and still a little too purple for my liking. I’ve gone and used the brush tool to selectively choose the water and adjusted the temperature to be a bit blue, tint to be a bit more green and then desaturated the water. I also reduced the clarity to give it a smoother feel – after all, this was a rushing river, so let’s give it that smooth, flowing feeling.
The Final Countdown
What you realise very early on with post-processing is that getting an image about 90% towards your ideal image is relatively easy…it’s that final 10% that takes time. You find experienced photographers will dwell over an image for an age trying to get it ‘perfect’. There has to be a time to stop and reflect. Once I’ve done all the finer details, I like to stop for a while, switch off Lightroom and do something else for a while. Then, return to the image and see how it looks. See if there are any image-wide adjustments that are worth doing. Whether I like the overall feel of it or not. This usually leads me to make some final adjustments and then post the pic to await the literally handful of people who like it to say so, or, I dump all my work and start again. You can muck around with an image for ages and not achieve anything, so just let it go and try again. Trust me, the more you play and practice the techniques the better you get, so use it as a learning experience, rather than a failure. So, here’s the final comparison between the starting image (cropped and rotated to match) and my final image. Now, time to have a go yourself and see how you go! Don’t forget to download the RAW file and have a play!
Feel free to comment with your processed image and ask any questions you have – I’ll do my best to answer them! Also, don’t forget to share this tutorial if you think it’d be useful to other budding astrophotographers.