Introduction to Siril

Simply Siril is a software for pre processing, registration & stacking with awesome post processing tools for astro images.

What make it special?

• Free
• Multiplatform (Mac, Linux & Windows)
• Professional processing tools

To download latest version, click here


To simplify the processing steps and show you what you could achieve with it, Im going to demonstrate it with simple learning curve with just dark and light frames.

Here a single shot of Orion Nebula:

So, let's start ...


Part One: Preprocessing


If your frames are ROW files you have to convert them to FIT format. Open Siril, then click + button.

From drop down list select: ROW DSLR Camera Files
select all your dark frames then click open
Sequence name: dark_

Click Convert

When conversation is completed, click Sequence Tab and make sure dark_seq is selected

Click Stacking Tab, then select these parameters

Stacking Methods: Average stacking with rejection

Normalisation: No normalisation

Rejection:Winsorized Sigma Clipping 

Store result in file: masterDark.fit

Click start stacking

When stacking is finished; You should check Pixel rejection in channel approximately are 0.5 - 0.5. if not repeat stacking with different Sigma low and high value

Click File conversation Tab

Click < button to remove dark frames.
Click + button
From drop down list select: ROW DSLR Camera Files
Select all your light frames then click open
Sequence name: light_

Click Convert

When conversation is completed, click Sequence Tab and make sure light_seq is selected

Click Pre-processing Tab

Check Use dark
Click Browse, then select masterDark.fit
Check Enable Cosmetic Correction
Click Estimate
Hot should be between 9800 - 10000, if not play with - + in Hot Sigma

Click Start pre-processing

Click File conversation Tab

Then click < button to remove dark frames.
Click + button
Select all files with pp_ prefix
This time, Check Demosaicing
Sequence name: light_demo_

Then click Convert

When conversation is completed, click Sequence Tab and make sure light_demo_seq is selected

Click Registration Tab, and make sure these parameters are selected

Register all images from sequence
Choose registration method: Global Star Alignment (deep sky)
Algorithm: Bicubic

Click Go register

When registration is completed, click Sequence Tab and make sure r_light_demo_seq is selected

Click Stacking Tab, then select these parameters

Stacking Methods: Average stacking with rejection

Normalisation: Additive with scaling

Rejection:Winsorized Sigma Clipping 

Store result in file: M42.fit

Click: start stacking

Part Two: Post processing


From main menu, select Background Extraction

Select as many as you can background spots
Click Compute
make sure Subtraction is selected
Click Apply

From main menu, select Color Calibration

Select any dark area then click on use current selection for black reference then click Background Neutralization

For white reference, select the core of light area then click on use current selection then Apply

From main menu, select Remove Green Noise

Click Apply

From main menu, select Median Filter
Iteration: 2
Click Apply

From main menu, select Histogram Transformation, then click Apply autostretch algorithm to image, finally click Apply

From main menu, File, Save as TIFF 16 Bit for more processing or JPEC to publish the image.

The Final result:

For flat, Bias frames calibration and more post precessing techniques Siril's developers team published a well organized and more completed document, Check here.