PixInsight vs Siril vs AutoStakkert vs DeepSkyStacker: Cost and Learning Time (2026)

Choosing astrophotography software is harder than it should be. There are a dozen programs, most of them overlap, and the differences that matter are not the ones on the feature lists.

Below is what each one is for, what it costs, and the questions that decide which suits you. We make one of them, Akastroid, so keep that in mind as you read.

Our recommendation

For most people the answer is Akastroid: one app for deep sky, planets, the Moon and the Sun, on Mac, Windows and Linux. You drop in your frames and it grades, calibrates, stacks, removes the gradient, calibrates the colour and sharpens, with no settings to choose. The usual route needs four to six separate programs for the same result.

On the same Orion stack, Akastroid’s automatic finish measured a signal-to-noise of 402 against 87 for Siril’s standard workflow, with a sky gradient of 2.6% against 21.6% (the full comparison). It is free to try on your own data.

Choose PixInsight if you want to control every step by hand and will spend months learning it, or Siril if you want free software and are happy to learn the steps. The rest of this guide compares them in detail.

Three questions that decide it

What do you shoot? Deep sky and planetary are different problems with different mathematics. Stacking a nebula means aligning on stars and integrating for hours. Stacking Jupiter means grading thousands of video frames, keeping the lucky few and correcting the atmosphere’s local warp. A tool built for one is rarely right for the other.

How much do you want to decide yourself? Some programs hand you every parameter and expect you to understand each one. Others measure the data and choose. Both approaches are fine. The first suits you when you know exactly what you want. The second suits you when you do not know yet, or when you have four targets to get through before work.

How do you weigh time against money? There are free tools for every job here. They cost learning time instead, sometimes a lot of it.

Deep sky

PixInsight: around €300, and worth it if you will learn it

The most capable astrophotography software there is. Everything is implemented correctly, the mathematics is documented, and almost nothing is decided for you.

The learning curve is steep, whatever people who climbed it years ago tell you. Expect months before your PixInsight results beat what you were getting elsewhere. After those months, nothing else does quite what it does.

Best for maximum control, if you enjoy the technical side and will put in the months.

Siril: free, and very good

Open source, actively developed, and the strongest free deep-sky option by some way. Calibration, registration, stacking, background extraction and photometric color calibration are all there and all sound.

The interface asks more of you than a commercial tool, and a lot of its capability is in the scripting. Nothing is crippled or cut down.

Best for capable deep-sky processing at no cost, if you don’t mind a steeper start.

DeepSkyStacker: free, and does one job

It stacks, and it has stacked reliably for twenty years. It does not do the finishing, so you leave with a linear TIFF and take it somewhere else, usually Photoshop or GIMP.

Best for a dependable stacker, if you already have a finishing workflow elsewhere.

Astro Pixel Processor: €199 to own, or around €50 a year to rent

Good at the jobs that are tedious elsewhere: mosaics, multi-session integration, light pollution removal. People either like the interface or dislike it. Its mosaic handling is particularly good.

Best for mosaics and multi-session integration.

GraXpert: free, and does one thing very well

Gradient removal, using a machine-learning model that does better than most manual approaches. It is a single step you drop into a workflow, not a workflow.

Best for gradient removal as a single step in a larger workflow.

Planetary

AutoStakkert: free, and the standard

Grades frames, keeps the sharpest, aligns on multiple points across the disc, stacks. It is the reference implementation of lucky imaging and it is free. Almost every good planetary image you have seen went through it.

It does not sharpen. That is left to a second program, which is why the classic planetary workflow uses several tools.

Best for frame grading and multi-point stacking, if you are willing to build a workflow around it.

RegiStax: free, and the other half

Wavelet sharpening, which AutoStakkert leaves out. Stack in one, sharpen in the other: that is the classic planetary workflow. The wavelet sliders are confusing at first and then hard to do without.

Best for sharpening a stack produced elsewhere.

PIPP: free, and the preprocessor

Centers the planet, crops, converts formats, sorts frames before stacking. It handles the fiddly problems that make a capture awkward to process, which a modern pipeline should avoid creating in the first place.

Where Akastroid fits

Each program above covers part of the job. PixInsight and Siril process deep sky; AutoStakkert stacks planets and RegiStax sharpens them; PIPP prepares the video first and GraXpert handles gradients. A complete workflow means learning three or four programs and moving files between them.

Akastroid does deep sky, planets and the Moon in one program with one export. It measures the processing settings from your frames instead of asking for them: frame grading, calibration, registration, stacking method, gradient removal, color calibration and the stretch. There is no sigma to choose and no stretch to pick, and each decision is written into the log so you can see what it did and why.

For planets it uses multi-point alignment to remove the atmosphere’s local warp, ranks frames per point so each region of the disc uses its own best moments, integrates onto a finer grid and applies limb-measured restoration. Wavelet sharpening is built in.

The processing engine contains no networking code at all, so nothing leaves your computer. You can watch the network while it runs.

It costs $79 (launch price until 31 October) once for one computer, with every future version free, or $149 for two. The free tier has every feature and is capped at five processing runs and three exports, not by feature or frame count.

Which one to choose

• Most people, for any subject: Akastroid. Deep sky, planets, the Moon and the Sun in one app; point it at the folder and read the log afterwards to see what it did.
• Planets: Akastroid does grading, multi-point stacking and wavelets in one pass. The AutoStakkert and RegiStax chain still works if you already have it set up.
• You want to control every parameter yourself: PixInsight, and give it the months it asks for.
• You want free and will learn it: Siril for deep sky, AutoStakkert and RegiStax for planets.
• Mosaics across many sessions: Astro Pixel Processor, or Akastroid if the panels are already stacked.

What “best” means here

The best software is the one you are still using in six months. That is usually the one whose learning curve you can manage, not the one with the longest feature list.

Everything here is free to try, Akastroid included, and its free tier is not a time-limited trial. Try two or three on your own data rather than the sample sets, and keep the one that gives you an image you like from a process you can put up with.

If you want the same programs sorted by what you shoot (deep sky, planets, Moon, a smart telescope) rather than by name, see the astrophotography software picker.