> ## Documentation Index
> Fetch the complete documentation index at: https://docs.biom.science/llms.txt
> Use this file to discover all available pages before exploring further.

# SExtractor — Source Extraction

> Detect and measure astronomical sources in images.

# SExtractor

SExtractor (Source Extractor) is a tool for detecting and measuring sources (stars, galaxies, and other astronomical objects) in images. It generates catalogs with positions, fluxes, and morphological parameters.

## Input formats

`.fits`, `.fit`, `.png`, `.jpg`, `.jpeg`, `.tiff`

## Parameters

| Parameter                     | Range         | Default | Description                                             |
| ----------------------------- | ------------- | ------- | ------------------------------------------------------- |
| **Detection threshold**       | 0.1–100 sigma | 1.5     | Minimum significance above background for detection     |
| **Minimum area**              | 1–1000 pixels | 5       | Minimum connected pixel area for a source               |
| **Deblending sub-thresholds** | 1–128         | 32      | Number of thresholds for deblending overlapping sources |
| **Deblending min contrast**   | 0–1           | 0.005   | Minimum contrast for deblending                         |
| **Catalog format**            | JSON / CSV    | JSON    | Output catalog format                                   |

## Outputs

| Output         | Format      | Description                                                 |
| -------------- | ----------- | ----------------------------------------------------------- |
| Source catalog | JSON or CSV | Positions (RA/Dec or pixel), fluxes, magnitudes, morphology |
| Overlay image  | PNG         | Original image with detected sources marked (optional)      |

## Presets

| Preset               | Description                              |
| -------------------- | ---------------------------------------- |
| **High Sensitivity** | Lower threshold, detects fainter sources |
| **Conservative**     | Higher threshold, fewer false positives  |

## Compute requirements

| Resource | Requirement            |
| -------- | ---------------------- |
| GPU      | None — CPU only        |
| Duration | \~20 seconds per image |

## Catalog fields

The output catalog includes:

* **Position** — X, Y pixel coordinates (and RA/Dec if WCS is available)
* **Flux** — integrated flux and peak flux
* **Magnitude** — instrumental magnitude
* **Shape** — ellipticity, position angle, FWHM
* **Flags** — quality flags for each detection