Creating false colour solar images with Photoshop’s ‘Duotone’
About a year ago I purchased my first Hydrogen Alpha solar scope, perfect for taking detailed images of the Sun in our solar maximum year. With it, I bought a mono planetary camera to capture the view – a ZWO ASI120mm.
The first challenge I encountered in processing was to apply a good looking false colour image to the sun. I struggled to find any decent walkthroughs on how to do it online, hence my post here. I tried a number of things in Photoshop – photo filters, overlays, stripping channels; most of which didn’t work out too well. Little did I know, as is often the case, the answer was right in front of me and obvious to the eye.
Here’s a step by step of a great way to apply false pseudo colour to any greyscale image. This doesn’t just apply to mono cameras – you can use this technique if you’ve taken a colour image of the sun using a standard solar filter and a DSLR camera, just convert to greyscale to strip the existing colour.
To start, you should either have your image generated from a blending program like Registrax or AutoStakkert or RAW from your DSLR. I always apply most of the sharpening at the very start so I can finish the rest of the tweaks on top.
Open your image in Photoshop, and bring it down to 8-bits (Image > Mode > 8Bits), then ensure its greyscale (Image > Mode > Greyscale). These are both necessary to apply duotone.
Apply duo tone
After you’ve ensured you have a greyscale 8Bit image, you should then see the Duotone option come available under ‘Image > Mode > Duotone’. Apply this mode.
Duotone allows you to essentially apply a colour tone to parts of your image’s histogram. The two settings you use govern a) the colour, and b) which part of the histogram you’re applying it to by how much, using a curves format.
You can use ‘Duotone’ as is, but you’ll want to add various layers of colour to deepen the colour profile. Because of this I use ‘Quadtone’, so you’ll need to select that from the dropdown menu, which will then display 4 tone settings.
From here, the world is your oyster. You can play around with different colours at different curves and achieve some interesting results from the image. Personally, I use a black to help contrast along, and rich yellow for the highlights, and a mixture of two oranges at varying curves to achieve the general colour of the final image.
After your initial tone settings you can apply other techniques to polish the image off. I don’t touch the image much from this point, I find that the hard sharpening from the initial video blending does a good job, and the Duotone achieves the colour balance I’m after. You can however go further, perhaps tweaking your levels and curves, contrast and exposure to better the balance of the features. If you feel you can squeeze a bit more sharpness in the image, Photoshop’s ‘Smart Sharpen’ tool is a good way to add some subtle crispness.
It’s easy to get carried away at this point and oversharpen, overstretch and degrade the image. I tend to walk away from the computer at this point for a couple of hours and let me eyes retract. Coming back to the file and doing my final tweaks with a reset mind tends to yield me an image I’m much happier with.
It’s all the same process if you wan’t to achieve a gold disc:
Or if you’re capturing in Calcium line, or just want that look: