Flat on Astro Live Stacker

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.

⚡ 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.

Process Tab

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

The ALS processing settings are presented in the Preferences page Process tab

Overview

This tab contains only one section: Preprocess

It gathers the settings for all calibration tasks:

Preferences page Process tab

Preprocess

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

Overview

The Preprocess pipeline handles calibration processes

Configuration

The Preprocess pipeline itself requires no configuration.

The configuration of the calibration processes is managed by the processes themselves. See the Behavior section below.

Control

The Preprocess module is launched in the background at ALS startup

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

Input

Data	Type
sub at queue front	Image

Behavior

Performs calibration processes on the sub:

Output

Calibrated sub is broadcast

Flat Calibration

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

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

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