AkastroidMono and narrowband
From filter stacksto the Hubble palette.
Give Akastroid one stack per filter. It recognises which is which, registers them on their stars and builds LRGB, SHO, HOO or HSO colour - with every hue traced to something you actually measured.
Free to try. Nothing is uploaded, and there is no account to create.
A mono camera sees no colour at all
That is its strength: every pixel measures light, none is spent behind a coloured filter it does not need. The colour comes from shooting the same target through several filters and combining them afterwards - and that combining step is where most people first open a second program and a tutorial.
In Akastroid it is one screen. Choose the files, check the channel each landed in, pick a palette, and compose.
The palettes
LRGB
Red, green and blue filters, with an optional luminance layer.
Natural colour, with the detail of a long luminance stack.
SHO
SII to red, Hα to green, OIII to blue.
The Hubble palette: gold, teal and blue out of three emission lines.
HOO
Hα to red, OIII to both green and blue.
Red against cyan - the natural choice for two filters or a dual-band capture.
HSO
Hα to red, SII to green, OIII to blue.
A warmer alternative to SHO from the same three files.
By hand
Any file to any channel, with a strength for each.
When you know exactly the look you want.
Filters recognised, not typed in
Each file's filter is read from its header or its name, in every spelling capture software uses, so an Hα, OIII and SII set usually lands in the right slots before you touch anything. Change any of them with one click; the palette then reassigns the whole set.
Registered on their stars
Filters are shot hours or nights apart, and the stacks rarely line up exactly. They are aligned on their stars before anything is combined - different sizes onto the largest - and a file that cannot be matched is left out and named, never blended in half a pixel wrong.
Honest about what is measured
Two filters make a real image. When a colour channel has no filter behind it, the app says so: a missing green is interpolated between the bands you have, a missing red or blue borrowed from the nearest, and saturation held back so the picture does not split into two complementary colours. Filters with no red, green or blue equivalent are ordered by wavelength, and you are told the hues represent wavelength rather than what the eye would see.
Dual-band on a colour camera
If you shoot a one-shot-colour camera through an L-eXtreme, L-Enhance, ALP-T, NBZ or similar filter, you do not need the composer: Deep Sky recognises the filter and leaves the star colours alone instead of balancing them to white, which is what usually turns a dual-band image muddy.
The narrowband basics - what each line is, which targets they suit - are in the guide to narrowband filters. The stacks themselves come from the deep-sky workflow.
What do I give it - raw frames or stacks?
One stacked file per filter, FITS or XISF: your Hα stack, your OIII stack, and so on. Stack each filter first (in Deep Sky, or wherever you stack); the composer turns the set into one colour image.
Does it know which file is which filter?
Usually. The filter is read from the file's header or its name - Ha, H-alpha, OIII, O3, SII, R, G, B, L and the other spellings capture software writes, dual-band names like Ha-OIII included. Anything it cannot tell is left unassigned for you to choose rather than guessed.
My filters were shot on different nights and the frames do not line up.
They are registered on their stars before they are combined. Files of different sizes are matched onto the largest, and a file that cannot be matched is left out and named rather than blended in misaligned. If your stacks are already aligned, say so and that step is skipped.
I only have Hα and OIII. Is that enough?
Yes - that is the HOO palette, and it is a complete image, not one with a channel missing. OIII fills both green and blue, so the result is Hα red against OIII cyan. With only two of three colour channels in any other palette, the missing one is interpolated and the colour held back so it does not split into two complementary hues.
What about a dual-band filter on a colour camera?
That goes through Deep Sky, not the composer, and it is recognised: L-eXtreme, L-Enhance, ALP-T, NBZ and similar filters are detected from the filter name, and data whose stars come out far from neutral is treated the same way. Their stars are not forced to white - which is what normally wrecks a dual-band image - and only the background is neutralised.
Is this in the free version?
Yes. Every feature is in the free version, with five processing runs and three exports to try it on your own data.
Your filter stacks, in colour, tonight.
Free to try on your own data. Nothing is uploaded.