PixInsight vs Siril: Which Should You Learn?

Two programs come up whenever someone asks what to process astrophotos with, and they are quite different. PixInsight costs around €300 and is the deepest processing environment in the hobby. Siril is free, open source, and covers the whole ordinary workflow well.

We make a third program, so take the recommendation with that in mind. The comparison below is the one we would give a friend.

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.

The short answer

If you want a finished image from your own data without learning either program, use Akastroid (see above). Between the two of them:

Learn Siril if you are starting out, if budget matters, or if you want a complete workflow without months of study. It calibrates, registers, stacks, removes gradients, plate-solves, photometrically color-calibrates, stretches and denoises. For most people, most of the time, the result is limited by the data rather than by Siril.

Learn PixInsight if processing is part of the hobby for you rather than a chore, if you shoot enough hours that the last ten percent matters, or if you need masking and pixel maths that nothing else offers.

Cost

Siril: free, GPL, no limits, no account.

PixInsight: a one-time licence, around €300, which includes a year of updates. The software keeps working after that, but further updates need renewing. That is expensive next to free and cheap next to a filter wheel. The larger cost is the learning time.

Learning curve

For most people this is the difference that decides it.

Siril gives you a script menu. “OSC_Preprocessing” takes a folder of lights, darks, flats and biases and returns a stacked image without you needing to know what any stage did. From there you learn the manual steps one at a time.

PixInsight presents dozens of processes with dozens of parameters each, and no default path through them. The documented workflow (WBPP, then DBE, then SPCC, then a stretch, then noise reduction, then deconvolution with a mask) is a sequence you have to learn before you get a picture you like, and it commonly takes months. People who get through it rarely go back. People who give up on it usually give up early.

What PixInsight does better

• Masking. Applying a process to only part of an image, such as the nebula but not the stars, or the core but not the outskirts. Nothing else matches it here, and much of the “how did they do that” in a great image is a mask.
• PixelMath. Arbitrary arithmetic across images. Narrowband palettes like Foraxx, custom star recombination and continuum subtraction are all PixelMath expressions.
• Deconvolution and noise reduction. BlurXTerminator and NoiseXTerminator are PixInsight add-ons (paid, and sold separately), and they are ahead of what free tools do.
• Repeatability. Process containers and icons let you save an exact workflow and apply it unchanged to the next session.

What Siril does better

• Getting to a result on day one. The scripts are a real on-ramp, and a beginner has a stacked image the first evening.
• Being free, on everything. Windows, macOS, Linux.
• Speed and size. It is light, starts fast, and does not need a fast machine.
• Plate solving and photometric color calibration, built in and free. Not long ago that was a paid-tool feature.

Where they are level

Calibration, registration, stacking with sigma rejection, gradient removal and a first stretch. On an average session, a careful Siril image and a careful PixInsight image differ less than either differs from the same data processed badly. Most “PixInsight images look better” comparisons are really comparisons of the processor’s experience.

Planets

Neither is a planetary tool. Planetary work is lucky imaging (grading thousands of video frames, multi-point alignment, wavelet sharpening), and that means AutoStakkert plus RegiStax, or one application that does both. If you shoot planets as well as deep sky, neither of these two covers everything.

A third option

If your actual obstacle is the sequence itself (folders of unprocessed frames, a dozen tutorials open, no finished image), then choosing between two expert tools may be the wrong question. That is what Akastroid is for. It measures your frames and sets the parameters from them, on Mac, Windows and Linux, and it does planetary as well. It has a lower ceiling than PixInsight, and we say so on the comparison page. There is a Siril comparison too, written the same way.

The free tier lets you try it before paying anything, and Siril costs nothing to try either, so you can find out which one fits your evenings.

The short version

• Akastroid if you want the picture rather than the learning: one app, no settings, deep sky, planets, the Moon and the Sun.
• Siril if you are starting and want free software, or if free and complete matters more to you than depth. It is good software.
• PixInsight if you want the ceiling and will spend months reaching it. Masking and PixelMath are the main reasons.
• They are far closer on an average night than the internet suggests. Experience is the bigger variable.
• Neither does planetary work. That needs a different toolchain.