Astro Live Stacker

Installation on PC/Linux

Thu, 11 Jun 2026 00:08:20 +0000

🖥️ Minimum System Requirements

64-bit GNU/Linux Distribution

Ubuntu 22.04 or higher
Fedora 34 or higher
Debian 11 (Bullseye) or higher
openSUSE Leap 15.3 or higher
Linux Mint 21 or higher
any other distribution offering GLIBC 2.35 or higher

Hardware Requirements

	Minimum
RAM	4 GB
Free Storage	950 MB

📦 Installation

Open the Downloads folder
- Access your Downloads folder. You can usually find it by clicking on the icon of your file manager (for example, Nautilus, Dolphin, or Thunar) and selecting “Downloads” in the navigation menu on the left.
Identify the ALS file

Installation on Raspberry Pi

Thu, 11 Jun 2026 00:08:20 +0000

🖥️ Minimum System Requirements

64-bit GNU/Linux Distribution*

Raspberry Pi OS - Bullseye (Version 11)
Raspberry Pi OS - Bookworm
any other distribution offering GLIBC 2.31 or higher

Hardware Requirements

	Minimum
Model	Pi 4 Model B
RAM	4 GB
Free Storage	650 MB

*The ALS versions available for download for Raspberry Pi are intended for 64-bit systems. However, you can easily adapt this build script to package a 32-bit version of ALS from the source. The only strict requirement is to use Python version 3.6.x. Feel free to contact us if you need assistance.

Install on Windows

Thu, 11 Jun 2026 00:08:20 +0000

🖥️ Minimum System Requirements

System Version

Windows 10 or higher

Hardware Requirements

	Minimum
RAM	4 GB
Free Storage	400 MB

📦 Installation

Open the Downloads Folder
- Once the download is complete, open File Explorer by clicking its icon on the taskbar (an icon shaped like a folder).
- Navigate to your Downloads folder by selecting “Downloads” in the navigation menu on the left.
- You should see the installer file that starts with als and ends with _Setup.exe. For example, it might be als-v0.7_Setup.exe.
Run the Installer

Installation on a Mac Apple Silicon

Thu, 11 Jun 2026 00:08:20 +0000

🖥️ Minimum System Requirements

System Version

macOS 10.13 (High Sierra) or later

Hardware Requirements

	Minimum
RAM	4 GB
Free Storage	400 MB

📦 Installation

Open the Downloads folder
- When the download is complete, open Finder by clicking on its icon in the Dock.
- Access your Downloads folder by selecting “Downloads” in the navigation menu on the left.
Identify the ALS disk image
- Look for the disk image whose name starts with als and ends with -arm64.dmg. For example, it might be als-v0.7-arm64.dmg.
Mount the disk image

Installation on a Mac Intel

Thu, 11 Jun 2026 00:08:20 +0000

🖥️ Minimum System Requirements

System Version

macOS 10.13 (High Sierra) or later

Hardware Requirements

	Minimum
RAM	4 GB
Free Storage	400 MB

📦 Installation

Open the Downloads folder
- When the download is complete, open Finder by clicking on its icon in the Dock.
- Access your Downloads folder by selecting “Downloads” in the navigation menu on the left.
Identify the ALS disk image
- Look for the disk image whose name starts with als and ends with -amd64.dmg. For example, it might be als-v0.7-amd64.dmg.
Mount the disk image

Concepts

Thu, 11 Jun 2026 00:33:39 +0000

Introduction

By the end of this chapter, the basic concepts of ALS will be familiar to you.

You will understand what ALS does and how it does it.

Stacking

Stacking is the process of combining multiple subs of the same target to generate a more detailed and contrasted image than a single sub.

The quality of the result increases as more subs are used.

Comparison of 8 stacking results
The number of stacked subs is indicated at the top left of each image

A successful session

Thu, 11 Jun 2026 00:33:39 +0000

📘 Introduction

This chapter is your roadmap for running a successful ALS session and monitoring its progress.

It wraps up the presentation of ALS main concepts before you dive into the user interface guide.

⚙️ Setup

Whether you’re shooting DSO live, preparing data for detailed post-processing, or diving into something more artistic, these steps will help you get the best out of ALS every time.

✔️ Choose Your Profile

EAA: For live imaging

Keyboard Shortcuts

Thu, 11 Jun 2026 00:46:48 +0000

ALS

Ctrl + P Preferences

Ctrl + Q Quit

ALS

⌘ + , Preferences

⌘ + Q Quit

Window

D toggles full screen mode

N toggles night mode

Livestacking

R starts / pauses / resumes the session

X stops the session

A ON/OFF subs alignment

K acknowledges issues

Panels

C ON/OFF toggle Main Controls

L ON/OFF toggle Session Log

P ON/OFF toggle Processing

I ON/OFF image-only mode

Image

Y zoom in

Scanner

Thu, 11 Jun 2026 00:33:39 +0000

Overview

The Scanner module is the entry point for your subs in ALS.

It is responsible for:

Monitoring the appearance of subs in the scan folder
Loading the detected subs

ℹ️ Existing files are ignored

Files present in the scan folder before the Scanner module is started are not detected

ℹ️ Detection of subs is recursive

Subs are detected regardless of the level of subfolders where they appear within the scan folder

Hot Pixel Removal

Thu, 11 Jun 2026 00:33:39 +0000

Overview

The HotPixelRemove process removes hot pixels from the image.

Its configuration is managed via ALS preferences.

Configuration

	Source	Data Type	Required	Default
ON/OFF	Preferences: Processing Tab	ON/OFF	∅	OFF

Control

This process is controlled by the Preprocess pipeline.

Input

Data	Type
image provided by the Preprocess pipeline	Image

Behavior

graph LR

START([START])

TEST_ENABLED{{Process enabled?}}
TEST_COLOR{{Color image?}}

COMPUTE[Compute average value of neighbors of each pixel]
REPLACE[Replace hot pixel value with the average of its neighbors]

RETURN[Return modified image]
UNCHANGED[Return unchanged image]

END([END])

START --> TEST_ENABLED
TEST_ENABLED -->|Yes| TEST_COLOR
TEST_COLOR ---->|Yes| UNCHANGED
TEST_ENABLED ---->|No| UNCHANGED
TEST_COLOR -->|No| COMPUTE
COMPUTE --> REPLACE
REPLACE --> RETURN
RETURN --> END
UNCHANGED --> END

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classDef wait  fill: #444, stroke: #262,stroke-width: 2px, color: #c6c6c6, font-family:'Poppins', sans-serif
classDef test fill: #444, stroke: #226, stroke-width: 2 px, color: #c6c6c6, font-family: 'Poppins', sans-serif

class START bounds
class TEST_ENABLED test
class TEST_COLOR test
class COMPUTE step
class UNCHANGED step
class REPLACE step
class RETURN step
class END bounds

Each pixel in the image whose value deviates too much from its neighbors is considered a hot pixel.

Dark Subtraction

Thu, 11 Jun 2026 00:33:38 +0000

Overview

The DarkRemove process subtracts the thermal noise from the image using a user-provided master dark.

Its configuration is managed via ALS preferences page.

Configuration

	Source	Data type	Required	Default value
ON/OFF	Preferences: Processing Tab	ON/OFF	∅	OFF
Master dark path	Preferences: Processing Tab	File path	Yes	∅

Control

This process is triggered by the Preprocess pipeline.

Input

Data	Type
image received from the Preprocess pipeline	Image
master dark read from configured path	Image

Behavior

graph LR

START([START])

TEST_ENABLED{{Processing enabled?}}
TEST_SIZE{{Identical dimensions?}}
TEST_TYPE{{Identical data types?}}

CONVERT[Convert master dark]
SUBTRACT[Subtract master dark from image]

RETURN[Return modified image]
UNCHANGED[Return unchanged image]

END([END])

START --> TEST_ENABLED

TEST_ENABLED ----->|No| UNCHANGED
TEST_ENABLED -->|Yes| TEST_SIZE

TEST_SIZE ----->|No| UNCHANGED
TEST_SIZE -->|Yes| TEST_TYPE

TEST_TYPE -->|No| CONVERT
TEST_TYPE -->|Yes| SUBTRACT

CONVERT --> SUBTRACT
SUBTRACT --> RETURN

RETURN --> END
UNCHANGED --> END

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classDef step fill: #444, stroke: #622, stroke-width:2px, color: #c6c6c6, font-family: 'Poppins',sans-serif
classDef wait  fill: #444, stroke: #262,stroke-width: 2px, color: #c6c6c6, font-family:'Poppins', sans-serif
classDef test fill: #444, stroke: #226, stroke-width: 2px, color: #c6c6c6, font-family: 'Poppins', sans-serif

class TEST_ENABLED,TEST_SIZE,TEST_TYPE test
class START,END bounds
class RETURN,UNCHANGED,CONVERT,SUBTRACT step

The master dark is subtracted from the image.

Debayering

Thu, 11 Jun 2026 00:33:38 +0000

Overview

The Debayer process is used on color images in FITS or Raw format.

It generates a color image from the raw image and the description of the Bayer pattern installed on the sensor that generated the image.

Its configuration is managed via ALS preferences page.

Configuration

	Source	Data Type	Required	Default Value
Bayer pattern	Preferences: Processing Tab	choice: - AUTO - GRBG - RGGB - GBRG - BGGR	YES	AUTO

Control

This process is triggered by the Preprocess module.

Stacker

Thu, 11 Jun 2026 00:33:39 +0000

Overview

The Stacker module handles the alignment and stacking of calibrated subs.

Configuration

	Source	Data type	Required	Default value
Alignment ON/OFF	Interface: Stacking controls	ON/OFF	∅	ON
Stacking mode	Interface: Stacking controls	choices: - mean - sum	YES	mean
Detection threshold	Interface: Stacking controls	integer	YES	25

Control

The Stack module is launched in the background at ALS startup

Source	Type	Response
sub(s) in queue	Event	trigger processing

Input

Data	Type
sub at queue front	Image
session alignment reference	Image

Behavior

flowchart LR
Start([START])
FirstSub{{First sub of the session?}}
SetAlignReference[Set sub as alignment reference]
CheckShape{{Sub same dimensions as previous result?}}
CheckAlign{{Alignment ON?}}
AlignImage[Align sub]
StackImage[Add sub to Stack]
ComputeStacking[Compute stacking]
PublishReference[Return alignment reference]
PublishResult[Return generated image]
End([END])

Start --> FirstSub
FirstSub -- YES --> SetAlignReference
SetAlignReference --> PublishReference
FirstSub -- NO --> CheckShape
CheckShape -- YES --> CheckAlign
CheckAlign -- YES --> AlignImage
AlignImage --> StackImage
CheckAlign -- NO --> StackImage
StackImage --> ComputeStacking
ComputeStacking --> PublishResult
CheckShape -- NO --> End
PublishReference --> End
PublishResult --> End

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classDef step fill: #444, stroke: #622, stroke-width:2px, color: #c6c6c6, font-family: 'Poppins',sans-serif
classDef test fill: #444, stroke: #226, stroke-width: 2px, color: #c6c6c6, font-family: 'Poppins', sans-serif

class Start,End bounds
class SetAlignReference,AlignImage,StackImage,PublishResult,ComputeStacking,PublishReference step
class CheckShape,CheckAlign,FirstSub test

Alignment

If alignment is ON

Auto-Stretch

Thu, 11 Jun 2026 00:33:39 +0000

Overview

The Auto-Stretch process optimizes the intensity levels of stacked images, making them visually usable without manual adjustments.

This process is handled by the Process pipeline module.

Configuration

Adjustments can be made through the Processing Panel, located on the right-hand side of the ALS interface.

Control	Type	Action
`Active`	checkbox	Enable or disable the process
`Strength`	slider	Adjust stretch intensity

Refer to the Processing Panel documentation for detailed instructions

Control

The Auto-Stretch process is managed by the Process pipeline

Levels

Thu, 11 Jun 2026 00:33:39 +0000

Overview

The Levels process adjusts the brightness distribution of a stacked image by setting black and white points and tuning midtones.
It allows precise control over image contrast and luminosity, complementing the Auto-Stretch process.

This process is handled by the Process pipeline module.

Configuration

The Levels process parameters are available in the Processing Panel, located on the right-hand side of the ALS interface.

Refer to the Processing Panel documentation for detailed instructions.

RGB Balance

Thu, 11 Jun 2026 00:33:39 +0000

Overview

The RGB Balance process adjusts the relative intensity of the three primary colors — red, green, and blue — to correct or refine the overall color tone of a stacked image.
It allows fine control of image chromatic balance, complementing the Levels and Auto-Stretch processes.

This process is handled by the Process pipeline module.

ℹ️ The RGB Balance process is only available when working with color images.

Configuration

The RGB Balance parameters are available in the Processing Panel, located on the right-hand side of the ALS interface.

Save

Wed, 10 Jun 2026 23:25:49 +0000

Overview

The Save module handles the saving on disk of all images generated by ALS.

Its configuration is managed via ALS preferences

Configuration

	Source	Data type	Required	Default value
work folder	Prefs: Output Tab	path to a folder	Yes	∅
web folder	Prefs: Output Tab	path to a folder	Yes	= work folder
file format	Prefs: Output Tab	choices: - TIFF - PNG - JPEG	Yes	JPEG

Control

The Save module is launched in the background at ALS startup

Server

Thu, 11 Jun 2026 00:20:09 +0000

Overview

The Server utility module exposes ALS processing results through a lightweight HTTP and WebSocket service.

It is responsible for:

Publishing the latest processed stacking result and session metrics in the configured web folder
Serving the viewer web application (index.html, JavaScript and icons)
Streaming live new-image notifications to connected browsers over WebSockets
Providing a QR-code friendly URL so that tablets or phones can join the session quickly

The module runs in its own asyncio event loop and accepts concurrent browser clients. It never alters the processing pipeline; it only serves the web image written by the Save module.

Installation on PC/Linux

Thu, 11 Jun 2026 00:08:20 +0000

🖥️ Minimum System Requirements

64-bit GNU/Linux Distribution

Ubuntu 22.04 or higher
Fedora 34 or higher
Debian 11 (Bullseye) or higher
openSUSE Leap 15.3 or higher
Linux Mint 21 or higher
any other distribution offering GLIBC 2.35 or higher

Hardware Requirements

	Minimum
RAM	4 GB
Free Storage	950 MB

📦 Installation

Open the Downloads folder
- Access your Downloads folder. You can usually find it by clicking on the icon of your file manager (for example, Nautilus, Dolphin, or Thunar) and selecting “Downloads” in the navigation menu on the left.
Identify the ALS file

Installation on Raspberry Pi

Thu, 11 Jun 2026 00:08:20 +0000

🖥️ Minimum System Requirements

64-bit GNU/Linux Distribution*

Raspberry Pi OS - Bullseye (Version 11)
Raspberry Pi OS - Bookworm
any other distribution offering GLIBC 2.31 or higher

Hardware Requirements

	Minimum
Model	Pi 4 Model B
RAM	4 GB
Free Storage	650 MB

Install on Windows

Thu, 11 Jun 2026 00:08:20 +0000

🖥️ Minimum System Requirements

System Version

Windows 10 or higher

Hardware Requirements

	Minimum
RAM	4 GB
Free Storage	400 MB

📦 Installation

Open the Downloads Folder
- Once the download is complete, open File Explorer by clicking its icon on the taskbar (an icon shaped like a folder).
- Navigate to your Downloads folder by selecting “Downloads” in the navigation menu on the left.
- You should see the installer file that starts with als and ends with _Setup.exe. For example, it might be als-v0.7.1_Setup.exe.
Run the Installer

Installation on a Mac Apple Silicon

Thu, 11 Jun 2026 00:08:20 +0000

🖥️ Minimum System Requirements

System Version

macOS 10.13 (High Sierra) or later

Hardware Requirements

	Minimum
RAM	4 GB
Free Storage	400 MB

📦 Installation

Open the Downloads folder
- When the download is complete, open Finder by clicking on its icon in the Dock.
- Access your Downloads folder by selecting “Downloads” in the navigation menu on the left.
Identify the ALS disk image
- Look for the disk image whose name starts with als and ends with -arm64.dmg. For example, it might be als-v0.7.1-arm64.dmg.
Mount the disk image

Installation on a Mac Intel

Thu, 11 Jun 2026 00:08:20 +0000

🖥️ Minimum System Requirements

System Version

macOS 10.13 (High Sierra) or later

Hardware Requirements

	Minimum
RAM	4 GB
Free Storage	400 MB

📦 Installation

Open the Downloads folder
- When the download is complete, open Finder by clicking on its icon in the Dock.
- Access your Downloads folder by selecting “Downloads” in the navigation menu on the left.
Identify the ALS disk image
- Look for the disk image whose name starts with als and ends with -amd64.dmg. For example, it might be als-v0.7.1-amd64.dmg.
Mount the disk image

Concepts

Thu, 11 Jun 2026 00:33:38 +0000

Introduction

By the end of this chapter, the basic concepts of ALS will be familiar to you.

You will understand what ALS does and how it does it.

Stacking

Stacking is the process of combining multiple subs of the same target to generate a more detailed and contrasted image than a single sub.

The quality of the result increases as more subs are used.

Comparison of 8 stacking results
The number of stacked subs is indicated at the top left of each image

A successful session

Thu, 11 Jun 2026 00:33:38 +0000

📘 Introduction

This chapter is your roadmap for running a successful ALS session and monitoring its progress.

It wraps up the presentation of ALS main concepts before you dive into the user interface guide.

⚙️ Setup

Whether you’re shooting DSO live, preparing data for detailed post-processing, or diving into something more artistic, these steps will help you get the best out of ALS every time.

✔️ Choose Your Profile

EAA: For live imaging

Keyboard Shortcuts

Thu, 11 Jun 2026 00:46:48 +0000

ALS

Ctrl + P Preferences

Ctrl + Q Quit

ALS

⌘ + , Preferences

⌘ + Q Quit

Window

D toggles full screen mode

N toggles night mode

Livestacking

R starts / pauses / resumes the session

X stops the session

A ON/OFF subs alignment

K acknowledges issues

Panels

C ON/OFF toggle Main Controls

L ON/OFF toggle Session Log

P ON/OFF toggle Processing

I ON/OFF image-only mode

Image

Y zoom in

Scanner

Thu, 11 Jun 2026 00:33:38 +0000

Overview

The Scanner module is the entry point for your subs in ALS.

It is responsible for:

Monitoring the appearance of subs in the scan folder
Loading the detected subs

ℹ️ Existing files are ignored

Files present in the scan folder before the Scanner module is started are not detected

ℹ️ Detection of subs is recursive

Subs are detected regardless of the level of subfolders where they appear within the scan folder

Hot Pixel Removal

Thu, 11 Jun 2026 00:33:38 +0000

Overview

The HotPixelRemove process removes hot pixels from the image.

Its configuration is managed via ALS preferences.

Configuration

	Source	Data Type	Required	Default
ON/OFF	Preferences: Processing Tab	ON/OFF	∅	OFF

Control

This process is controlled by the Preprocess pipeline.

Input

Data	Type
image provided by the Preprocess pipeline	Image

Behavior

graph LR

START([START])

TEST_ENABLED{{Process enabled?}}
TEST_COLOR{{Color image?}}

COMPUTE[Compute average value of neighbors of each pixel]
REPLACE[Replace hot pixel value with the average of its neighbors]

RETURN[Return modified image]
UNCHANGED[Return unchanged image]

END([END])

START --> TEST_ENABLED
TEST_ENABLED -->|Yes| TEST_COLOR
TEST_COLOR ---->|Yes| UNCHANGED
TEST_ENABLED ---->|No| UNCHANGED
TEST_COLOR -->|No| COMPUTE
COMPUTE --> REPLACE
REPLACE --> RETURN
RETURN --> END
UNCHANGED --> END

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classDef wait  fill: #444, stroke: #262,stroke-width: 2px, color: #c6c6c6, font-family:'Poppins', sans-serif
classDef test fill: #444, stroke: #226, stroke-width: 2 px, color: #c6c6c6, font-family: 'Poppins', sans-serif

class START bounds
class TEST_ENABLED test
class TEST_COLOR test
class COMPUTE step
class UNCHANGED step
class REPLACE step
class RETURN step
class END bounds

Each pixel in the image whose value deviates too much from its neighbors is considered a hot pixel.

Dark Subtraction

Thu, 11 Jun 2026 00:33:38 +0000

Overview

The DarkRemove process subtracts the thermal noise from the image using a user-provided master dark.

Its configuration is managed via ALS preferences page.

Configuration

	Source	Data type	Required	Default value
ON/OFF	Preferences: Processing Tab	ON/OFF	∅	OFF
Master dark path	Preferences: Processing Tab	File path	Yes	∅

Control

This process is triggered by the Preprocess pipeline.

Input

Data	Type
image received from the Preprocess pipeline	Image
master dark read from configured path	Image

Behavior

graph LR

START([START])

TEST_ENABLED{{Processing enabled?}}
TEST_SIZE{{Identical dimensions?}}
TEST_TYPE{{Identical data types?}}

CONVERT[Convert master dark]
SUBTRACT[Subtract master dark from image]

RETURN[Return modified image]
UNCHANGED[Return unchanged image]

END([END])

START --> TEST_ENABLED

TEST_ENABLED ----->|No| UNCHANGED
TEST_ENABLED -->|Yes| TEST_SIZE

TEST_SIZE ----->|No| UNCHANGED
TEST_SIZE -->|Yes| TEST_TYPE

TEST_TYPE -->|No| CONVERT
TEST_TYPE -->|Yes| SUBTRACT

CONVERT --> SUBTRACT
SUBTRACT --> RETURN

RETURN --> END
UNCHANGED --> END

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classDef step fill: #444, stroke: #622, stroke-width:2px, color: #c6c6c6, font-family: 'Poppins',sans-serif
classDef wait  fill: #444, stroke: #262,stroke-width: 2px, color: #c6c6c6, font-family:'Poppins', sans-serif
classDef test fill: #444, stroke: #226, stroke-width: 2px, color: #c6c6c6, font-family: 'Poppins', sans-serif

class TEST_ENABLED,TEST_SIZE,TEST_TYPE test
class START,END bounds
class RETURN,UNCHANGED,CONVERT,SUBTRACT step

The master dark is subtracted from the image.

Debayering

Thu, 11 Jun 2026 00:33:38 +0000

Overview

The Debayer process is used on color images in FITS or Raw format.

It generates a color image from the raw image and the description of the Bayer pattern installed on the sensor that generated the image.

Its configuration is managed via ALS preferences page.

Configuration

	Source	Data Type	Required	Default Value
Bayer pattern	Preferences: Processing Tab	choice: - AUTO - GRBG - RGGB - GBRG - BGGR	YES	AUTO

Control

This process is triggered by the Preprocess module.

Stacker

Thu, 11 Jun 2026 00:33:38 +0000

Overview

The Stacker module handles the alignment and stacking of calibrated subs.

Configuration

	Source	Data type	Required	Default value
Alignment ON/OFF	Interface: Stacking controls	ON/OFF	∅	ON
Stacking mode	Interface: Stacking controls	choices: - mean - sum	YES	mean
Detection threshold	Interface: Stacking controls	integer	YES	25

Control

The Stack module is launched in the background at ALS startup

Source	Type	Response
sub(s) in queue	Event	trigger processing

Input

Data	Type
sub at queue front	Image
session alignment reference	Image

Behavior

flowchart LR
Start([START])
FirstSub{{First sub of the session?}}
SetAlignReference[Set sub as alignment reference]
CheckShape{{Sub same dimensions as previous result?}}
CheckAlign{{Alignment ON?}}
AlignImage[Align sub]
StackImage[Add sub to Stack]
ComputeStacking[Compute stacking]
PublishReference[Return alignment reference]
PublishResult[Return generated image]
End([END])

Start --> FirstSub
FirstSub -- YES --> SetAlignReference
SetAlignReference --> PublishReference
FirstSub -- NO --> CheckShape
CheckShape -- YES --> CheckAlign
CheckAlign -- YES --> AlignImage
AlignImage --> StackImage
CheckAlign -- NO --> StackImage
StackImage --> ComputeStacking
ComputeStacking --> PublishResult
CheckShape -- NO --> End
PublishReference --> End
PublishResult --> End

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classDef step fill: #444, stroke: #622, stroke-width:2px, color: #c6c6c6, font-family: 'Poppins',sans-serif
classDef test fill: #444, stroke: #226, stroke-width: 2px, color: #c6c6c6, font-family: 'Poppins', sans-serif

class Start,End bounds
class SetAlignReference,AlignImage,StackImage,PublishResult,ComputeStacking,PublishReference step
class CheckShape,CheckAlign,FirstSub test

Alignment

If alignment is ON

Auto-Stretch

Thu, 11 Jun 2026 00:33:38 +0000

Overview

The Auto-Stretch process optimizes the intensity levels of stacked images, making them visually usable without manual adjustments.

This process is handled by the Process pipeline module.

Configuration

Adjustments can be made through the Processing Panel, located on the right-hand side of the ALS interface.

Control	Type	Action
`Active`	checkbox	Enable or disable the process
`Strength`	slider	Adjust stretch intensity

Refer to the Processing Panel documentation for detailed instructions

Control

The Auto-Stretch process is managed by the Process pipeline

Levels

Thu, 11 Jun 2026 00:33:38 +0000

Overview

This process is handled by the Process pipeline module.

Configuration

The Levels process parameters are available in the Processing Panel, located on the right-hand side of the ALS interface.

Refer to the Processing Panel documentation for detailed instructions.

RGB Balance

Thu, 11 Jun 2026 00:33:38 +0000

Overview

This process is handled by the Process pipeline module.

ℹ️ The RGB Balance process is only available when working with color images.

Configuration

The RGB Balance parameters are available in the Processing Panel, located on the right-hand side of the ALS interface.

Save

Wed, 10 Jun 2026 23:25:49 +0000

Overview

The Save module handles the saving on disk of all images generated by ALS.

Its configuration is managed via ALS preferences

Configuration

	Source	Data type	Required	Default value
work folder	Prefs: Output Tab	path to a folder	Yes	∅
web folder	Prefs: Output Tab	path to a folder	Yes	= work folder
file format	Prefs: Output Tab	choices: - TIFF - PNG - JPEG	Yes	JPEG

Control

The Save module is launched in the background at ALS startup

Server

Thu, 11 Jun 2026 00:20:09 +0000

Overview

The Server utility module exposes ALS processing results through a lightweight HTTP and WebSocket service.

It is responsible for:

Publishing the latest processed stacking result and session metrics in the configured web folder
Serving the viewer web application (index.html, JavaScript and icons)
Streaming live new-image notifications to connected browsers over WebSockets

The module runs in its own asyncio event loop and accepts concurrent browser clients. It never alters the processing pipeline; it only serves the web image written by the Save module.

Installation on PC/Linux

Thu, 11 Jun 2026 00:08:20 +0000

🖥️ Minimum System Requirements

64-bit GNU/Linux Distribution

Ubuntu 22.04 or higher
Fedora 34 or higher
Debian 11 (Bullseye) or higher
openSUSE Leap 15.3 or higher
Linux Mint 21 or higher
any other distribution offering GLIBC 2.35 or higher

Hardware Requirements

	Minimum
RAM	4 GB
Free Storage	950 MB

📦 Installation

Open the Downloads folder
- Access your Downloads folder. You can usually find it by clicking on the icon of your file manager (for example, Nautilus, Dolphin, or Thunar) and selecting “Downloads” in the navigation menu on the left.
Identify the ALS file

Installation on Raspberry Pi

Thu, 11 Jun 2026 00:08:20 +0000

🖥️ Minimum System Requirements

64-bit GNU/Linux Distribution*

Raspberry Pi OS - Bullseye (Version 11)
Raspberry Pi OS - Bookworm
any other distribution offering GLIBC 2.31 or higher

Hardware Requirements

	Minimum
Model	Pi 4 Model B
RAM	4 GB
Free Storage	650 MB

Install on Windows

Thu, 11 Jun 2026 00:08:20 +0000

🖥️ Minimum System Requirements

System Version

Windows 10 or higher

Hardware Requirements

	Minimum
RAM	4 GB
Free Storage	400 MB

📦 Installation

Open the Downloads Folder
- Once the download is complete, open File Explorer by clicking its icon on the taskbar (an icon shaped like a folder).
- Navigate to your Downloads folder by selecting “Downloads” in the navigation menu on the left.
- You should see the installer file that starts with als and ends with _Setup.exe . For example, it might be als-v1.0_Setup.exe .
Run the Installer

Installation on a Mac Apple Silicon

Thu, 11 Jun 2026 00:08:20 +0000

🖥️ Minimum System Requirements

System Version

macOS 10.13 (High Sierra) or later

Hardware Requirements

	Minimum
RAM	4 GB
Free Storage	400 MB

📦 Installation

Open the Downloads folder
- When the download is complete, open Finder by clicking on its icon in the Dock.
- Access your Downloads folder by selecting “Downloads” in the navigation menu on the left.
Identify the ALS disk image
- Look for the disk image whose name starts with als and ends with -arm64.dmg . For example, it might be als-v1.0-arm64.dmg .
Mount the disk image

Installation on a Mac Intel

Thu, 11 Jun 2026 00:08:20 +0000

🖥️ Minimum System Requirements

System Version

macOS 10.13 (High Sierra) or later

Hardware Requirements

	Minimum
RAM	4 GB
Free Storage	400 MB

📦 Installation

Open the Downloads folder
- When the download is complete, open Finder by clicking on its icon in the Dock.
- Access your Downloads folder by selecting “Downloads” in the navigation menu on the left.
Identify the ALS disk image
- Look for the disk image whose name starts with als and ends with -amd64.dmg . For example, it might be als-v1.0-amd64.dmg .
Mount the disk image

Concepts

Thu, 11 Jun 2026 00:33:39 +0000

Introduction

By the end of this chapter, the basic concepts of ALS will be familiar to you.

You will understand what ALS does and how it does it.

Stacking

Stacking is the process of combining multiple subs of the same target to generate a more detailed and contrasted image than a single sub.

The quality of the result increases as more subs are used.

Comparison of 8 stacking results
The number of stacked subs is indicated at the top left of each image

A successful session

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📘 Introduction

This chapter is your roadmap for running a successful ALS session and monitoring its progress.

It wraps up the presentation of ALS main concepts before you dive into the user interface guide.

⚡ Startup

ALS can be launched either from its graphical interface or directly from the command line, depending on your workflow or automation needs.

Graphical launch:
Simply start ALS as any other application. You’ll land in the main window, ready to configure your session.

Keyboard Shortcuts

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ALS

Ctrl + P Preferences

Ctrl + Q Quit

ALS

⌘ + , Preferences

⌘ + Q Quit

Window

F toggles full screen mode

Session

R starts / pauses / resumes the session

X stops the session

K acknowledges issues

Stacking

A ON/OFF subs alignment

M stacks in mean mode

S stacks in sum mode

Saving

T ON/OFF timelapse mode

D Save current result with timestamp

Panels

C ON/OFF toggle Main Controls

Scanner

Thu, 11 Jun 2026 18:38:13 +0000

Overview

The Scanner module is the entry point for your subs in ALS.

It is responsible for:

Monitoring the appearance of subs in the scan folder
Loading the detected subs

ℹ️ Existing files are ignored

Files present in the scan folder before the Scanner module is started are not detected

ℹ️ Detection of subs is recursive

Subs are detected regardless of the level of subfolders where they appear within the scan folder

Hot Pixel Removal

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Overview

The HotPixelRemove process removes hot pixels from the image.

Its configuration is managed via ALS preferences.

Configuration

	Source	Data Type	Required	Default
ON/OFF	Preferences: Processing Tab	ON/OFF	∅	OFF

Control

This process is controlled by the Preprocess pipeline.

Input

Data	Type
image provided by the Preprocess pipeline	Image

Behavior

graph LR

START([START])

TEST_ENABLED{{Process enabled?}}
TEST_COLOR{{Color image?}}

COMPUTE[Compute average value of neighbors of each pixel]
REPLACE[Replace hot pixel value with the average of its neighbors]

RETURN[Return modified image]
UNCHANGED[Return unchanged image]

END([END])

START --> TEST_ENABLED
TEST_ENABLED -->|Yes| TEST_COLOR
TEST_COLOR ---->|Yes| UNCHANGED
TEST_ENABLED ---->|No| UNCHANGED
TEST_COLOR -->|No| COMPUTE
COMPUTE --> REPLACE
REPLACE --> RETURN
RETURN --> END
UNCHANGED --> END

classDef bounds fill: #333, stroke: #666, stroke-width: 2px, color: #BBB, font-family: 'Poppins', sans-serif
classDef step fill: #444, stroke: #622, stroke-width:2px, color: #c6c6c6, font-family: 'Poppins',sans-serif
classDef wait  fill: #444, stroke: #262,stroke-width: 2px, color: #c6c6c6, font-family:'Poppins', sans-serif
classDef test fill: #444, stroke: #226, stroke-width: 2 px, color: #c6c6c6, font-family: 'Poppins', sans-serif

class START bounds
class TEST_ENABLED test
class TEST_COLOR test
class COMPUTE step
class UNCHANGED step
class REPLACE step
class RETURN step
class END bounds

Each pixel in the image whose value deviates too much from its neighbors is considered a hot pixel.

Dark Subtraction

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Overview

The DarkRemove process subtracts the thermal noise from the image using a user-provided master dark.

Its configuration is managed via ALS preferences page.

Configuration

	Source	Data type	Required	Default value
ON/OFF	Preferences: Processing Tab	ON/OFF	∅	OFF
Master dark path	Preferences: Processing Tab	File path	Yes	∅

Control

This process is triggered by the Preprocess pipeline.

Input

Data	Type
image received from the Preprocess pipeline	Image
master dark read from configured path	Image

Behavior

graph LR

START([START])

TEST_ENABLED{{Processing enabled?}}
TEST_SIZE{{Identical dimensions?}}
TEST_TYPE{{Identical data types?}}

CONVERT[Convert master dark]
SUBTRACT[Subtract master dark from image]

RETURN[Return modified image]
UNCHANGED[Return unchanged image]

END([END])

START --> TEST_ENABLED

TEST_ENABLED ----->|No| UNCHANGED
TEST_ENABLED -->|Yes| TEST_SIZE

TEST_SIZE ----->|No| UNCHANGED
TEST_SIZE -->|Yes| TEST_TYPE

TEST_TYPE -->|No| CONVERT
TEST_TYPE -->|Yes| SUBTRACT

CONVERT --> SUBTRACT
SUBTRACT --> RETURN

RETURN --> END
UNCHANGED --> END

classDef bounds fill: #333, stroke: #666, stroke-width: 2px, color: #BBB, font-family: 'Poppins', sans-serif
classDef step fill: #444, stroke: #622, stroke-width:2px, color: #c6c6c6, font-family: 'Poppins',sans-serif
classDef wait  fill: #444, stroke: #262,stroke-width: 2px, color: #c6c6c6, font-family:'Poppins', sans-serif
classDef test fill: #444, stroke: #226, stroke-width: 2px, color: #c6c6c6, font-family: 'Poppins', sans-serif

class TEST_ENABLED,TEST_SIZE,TEST_TYPE test
class START,END bounds
class RETURN,UNCHANGED,CONVERT,SUBTRACT step

The master dark is subtracted from the image.

Flat Calibration

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Overview

The RemoveFlat process divides each sub by a user-provided master flat to remove optical vignetting, dust motes, and pixel-to-pixel response variations.

Its configuration is managed via the ALS preferences page.

Configuration

	Source	Data type	Required	Default value
ON/OFF	Preferences: Processing Tab	ON/OFF	∅	OFF
Master flat path	Preferences: Processing Tab	File path	Yes	∅

Control

This process is triggered by the Preprocess pipeline.

Input

Data	Type
image received from the Preprocess pipeline	Image
master flat read from configured path	Image

Behavior

graph LR

START([START])

TEST_ENABLED{{Processing enabled?}}
READ_FLAT[Read master flat]
TEST_SHAPE{{Identical dimensions?}}
    NORMALIZE[Normalize by robust scale]
    SAFEGUARD[Apply epsilon floor]
DIVIDE[Divide image by normalized flat]
CLIP[Clip to 16-bit range]
RETURN[Return calibrated image]
UNCHANGED[Return unchanged image]

END([END])

START --> TEST_ENABLED

TEST_ENABLED ----->|No| UNCHANGED
TEST_ENABLED -->|Yes| READ_FLAT

READ_FLAT ----->|Failed| UNCHANGED
READ_FLAT -->|Ok| TEST_SHAPE

TEST_SHAPE ----->|No| UNCHANGED
TEST_SHAPE -->|Yes| NORMALIZE

NORMALIZE --> SAFEGUARD
SAFEGUARD --> DIVIDE
DIVIDE --> CLIP
CLIP --> RETURN

RETURN --> END
UNCHANGED --> END

classDef bounds fill: #333, stroke: #666, stroke-width: 2px, color: #BBB, font-family: 'Poppins', sans-serif
classDef step fill: #444, stroke: #622, stroke-width:2px, color: #c6c6c6, font-family: 'Poppins',sans-serif
classDef wait  fill: #444, stroke: #262,stroke-width: 2px, color: #c6c6c6, font-family:'Poppins', sans-serif
classDef test fill: #444, stroke: #226, stroke-width: 2px, color: #c6c6c6, font-family: 'Poppins', sans-serif

class TEST_ENABLED,TEST_SHAPE test
class START,END bounds
class RETURN,UNCHANGED,READ_FLAT,NORMALIZE,SAFEGUARD,DIVIDE,CLIP step

The master flat is loaded from disk, converted to a normalized float32 calibration frame, and protected with a small epsilon floor before dividing the sub.

Debayering

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Overview

The Debayer process is used on color images in FITS or Raw format.

It generates a color image from the raw image and the description of the Bayer pattern installed on the sensor that generated the image.

Its configuration is managed via ALS preferences page.

Configuration

	Source	Data Type	Required	Default Value
Bayer pattern	Preferences: Processing Tab	choice: - AUTO - GRBG - RGGB - GBRG - BGGR	YES	AUTO

Control

This process is triggered by the Preprocess module.

Stacker

Thu, 11 Jun 2026 17:57:08 +0000

Overview

The Stacker module handles the alignment and stacking of calibrated subs.

Configuration

	Source	Data type	Required	Default value
Alignment ON/OFF	Interface: Stacking controls	ON/OFF	∅	ON
Stacking mode	Interface: Stacking controls	choices: - mean - sum	YES	mean
Minimum matches	Interface: Stacking controls	integer	YES	25

Control

The Stack module is launched in the background at ALS startup

Source	Type	Response
sub(s) in queue	Event	trigger processing

Input

Data	Type
sub at queue front	Image
session alignment reference	Image

Behavior

flowchart LR
Start([START])
FirstSub{{First sub of the session?}}
SetAlignReference[Set sub as alignment reference]
CheckShape{{Sub same dimensions as previous result?}}
CheckAlign{{Alignment ON?}}
AlignImage[Align sub]
StackImage[Add sub to Stack]
ComputeStacking[Compute stacking]
PublishReference[Return alignment reference]
PublishResult[Return generated image]
End([END])

Start --> FirstSub
FirstSub -- YES --> SetAlignReference
SetAlignReference --> PublishReference
FirstSub -- NO --> CheckShape
CheckShape -- YES --> CheckAlign
CheckAlign -- YES --> AlignImage
AlignImage --> StackImage
CheckAlign -- NO --> StackImage
StackImage --> ComputeStacking
ComputeStacking --> PublishResult
CheckShape -- NO --> End
PublishReference --> End
PublishResult --> End

classDef bounds fill: #333, stroke: #666, stroke-width: 2px, color: #BBB, font-family: 'Poppins', sans-serif
classDef step fill: #444, stroke: #622, stroke-width:2px, color: #c6c6c6, font-family: 'Poppins',sans-serif
classDef test fill: #444, stroke: #226, stroke-width: 2px, color: #c6c6c6, font-family: 'Poppins', sans-serif

class Start,End bounds
class SetAlignReference,AlignImage,StackImage,PublishResult,ComputeStacking,PublishReference step
class CheckShape,CheckAlign,FirstSub test

Alignment

If alignment is ON

Auto-Stretch

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Overview

The Auto-Stretch process optimizes the intensity levels of stacked images, making them visually usable without manual adjustments.

This process is handled by the Process pipeline module.

Configuration

Adjustments can be made through the Processing Panel, located on the right-hand side of the ALS interface.

Control	Type	Action
`Active`	checkbox	Enable or disable the process
`Strength`	slider	Adjust stretch intensity

Refer to the Processing Panel documentation for detailed instructions

Control

The Auto-Stretch process is managed by the Process pipeline

Levels

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Overview

This process is handled by the Process pipeline module.

Configuration

The Levels process parameters are available in the Processing Panel, located on the right-hand side of the ALS interface.

Refer to the Processing Panel documentation for detailed instructions.

RGB Balance

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Overview

The RGB Balance process adjusts the relative intensity of the three primary colors — red, green, and blue — to correct or refine the overall color tone of a stacked image. It also controls global color saturation, letting you reinforce or tame chroma while keeping exposure unchanged. These parameters allow fine control of image chromatic balance, complementing the Levels and Auto-Stretch processes.

This process is handled by the Process pipeline module.

Save

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Overview

The Save module handles the saving on disk of all images generated by ALS.

Its configuration is managed via ALS preferences

Configuration

	Source	Data type	Required	Default value
work folder	Prefs: Output Tab	path to a folder	Yes	∅
web folder	Prefs: Output Tab	path to a folder	Yes	= work folder
file format	Prefs: Output Tab	choices: - TIFF - PNG - JPEG	Yes	JPEG

Control

The Save module is launched in the background at ALS startup

Server

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Overview

The Server utility module exposes ALS processing results through a lightweight HTTP and WebSocket service.

It is responsible for:

Publishing the latest processed stacking result and session metrics in the configured web folder
Serving the viewer web application (index.html, JavaScript and icons)
Streaming live new-image notifications to connected browsers over WebSockets
Providing a QR-code friendly URL so that tablets or phones can join the session quickly

The module runs in its own asyncio event loop and accepts concurrent browser clients. It never alters the processing pipeline; it only serves the web image written by the Save module.

🚀 ALS v1.0 — The Big One!

Wed, 10 Jun 2026 23:06:05 +0000

It’s finally happening.
After years of pixel-pushing, photon-wrangling, and late-night debugging under the stars, Astro Live Stacker is soon reaching version 1.0 — our first truly feature-complete release. 🥳

🌌 What’s new?

The highlight of this milestone: flat calibration.
Yep, the long-awaited ability to correct your subs using master flats is here — and it completes the calibration suite alongside master darks. With this, ALS officially checks all the boxes we’d dreamed of when the project began.

Donations

Sun, 02 Nov 2025 00:00:00 +0000

Support ALS

Astro Live Stacker (ALS) is a free, open-source project maintained on personal time. If ALS helps you, a small donation makes a big difference.

Donate via Ko-fi

How your donations are used

Hardware to reproduce & fix issues — e.g. purchase a Raspberry Pi 5 to investigate platform-specific bugs.
Hardware to build platform-specific releases — e.g. purchase a second-hand Intel-based Mac to ship and verify macOS Intel builds.
Coffee ☕ — fuel for development and documentation.

Thank you for helping ALS reach more astro-imagers with better builds, faster fixes, and clearer docs.

Astro Live Stacker 0.7 — A New Light in the Sky

Mon, 27 Oct 2025 00:00:00 +0000

For a while, the stars went quiet.
But with version 0.7, Astro Live Stacker shines again — rebuilt, refined, and ready to make your nights under the sky smoother than ever.

This release is the result of several years of patient work, endless cups of coffee, and a stubborn love for both code and starlight.
It marks a turning point for ALS: cleaner, more capable, fully documented, and finally ready for everyone.

Frequently Asked Questions

Thu, 23 Oct 2025 07:43:14 +0000

Frequently Asked Questions

Below you'll find answers to the most common questions about Astro Live Stacker (ALS). If you don't find what you're looking for, open an issue on GitHub or reach out via the community channels.

🧩 General

What is Astro Live Stacker (ALS)?

ALS is a real-time astrophotography tool that aligns and stacks images on the fly to improve signal-to-noise ratio and reveal faint details during live sessions.

Privacy Policy

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Privacy Policy

Who are we?

We are a non-profit organization dedicated to creating open-source software, which we publish for free with the sole purpose of being useful to our community. We don’t make any money from these projects; our mission is to ensure our tools are as beneficial as possible for everyone.

User Data Privacy

We don’t and will never share your information with anyone. Your privacy is our top priority.

ALS v0.7-beta10 is available in Russian

Thu, 23 Jan 2025 23:30:17 +0000

In the last few weeks, ALS seems to have raised interest in the Russian-speaking community.

We found the source: Mr. Eduard VAZHOROV, who published a very detailed guide about ALS on his blog. From there, the knowledge spread out.

Eduard VAZHOROV is a Russian amateur astronomer and professional web designer. He is best known for creating the Beginner’s Star Atlas v.2, a comprehensive sky atlas that plots stars up to the 7th magnitude and includes a variety of deep-sky objects (DSOs). The atlas is available for free in russian and in english

Hot Hot : ALS v0.7-beta10

Tue, 07 Jan 2025 16:31:56 +0000

We keep moving forward… Final touches before the release of version 0.7.

The application

New version available: v0.7-beta10

✨ changes:
- New server view
  - better image navigation
  - display of stack information: number of stacked subs and total exposure time
  - automatic update of the image and information with each new processing result
- User interface adjustments
  - Moved stack information to the Stack section of the main controls

New server view

New milestone : ALS v0.7-beta9

Fri, 03 Jan 2025 01:04:04 +0000

The app

Working on documentation for sure makes you tick…

So a couple fixes and improvements were made in ALS

Published in version v0.7-beta9

✨ what’s new:
- fix shortcuts for issue acknowledgement and fullscreen mode
- improve file read reliability
- reorganize preferences page
- disallow critical folders nesting

Everyting is looking tip top for release… sometime soon :)

Download the latest beta version from the homepage of this new site https://next.als-app.org.

Documentation

All settings are now documented in the Preferences section.

ALS v0.7 and new website

Sun, 29 Dec 2024 18:36:55 +0000

ALS version 0.7 is nearing completion after several years of development.

The last known bugs have been fixed.

We are now working on finalizing this new website, which will go live at https://als-app.org when the documentation is complete.

The documentation work is regularly published on this new site in the Documentation section.

You can download the latest beta version from the homepage of this new site https://next.als-app.org.

A bit more patience 😊 …

Contributors

Thu, 28 Nov 2024 12:36:00 +0200

Contributors

We are grateful to the following people for their valuable contributions

Benjamin FOUSSE

Project logo.

Davy HUBERT

Dark subtraction.
Minimum similarity threshold for stacking.

Christophe HEULIN

Shots for the screenshot.

Want to contribute to Astro Live Stacker?

Join the family!

About Astro Live Stacker

Wed, 27 Nov 2024 00:00:00 +0000

What is Astro Live Stacker?

Astro Live Stacker (ALS) is an open-source application dedicated to live astrophotography.

Its primary role is to enable real-time processing of astronomical images, a technique called livestacking.

This approach involves aligning and stacking successive images as they are acquired to enhance their quality by revealing more details and reducing noise.

ALS handles diverse image formats and runs seamlessly across desktop and embedded platforms — from Linux, Windows, and macOS to Raspberry Pi — and lets you share live stacking sessions through its integrated web server.