auto-stretch 1.1.0

Stretch linear astro data for easier visualization.

Auto Stretch

Automatically stretch linear astronomical images for easy visualization.

Auto Stretch applies a PixInsight-style Screen Transfer Function (STF) midtones transfer to linear astronomical images stored as numpy arrays. It automatically computes the optimal stretch parameters from the image data so that faint detail becomes visible without manual histogram adjustment.

linear (no stretch)	arcsin stretch	auto-stretch (using this library)

Installation

pip install auto-stretch

Quickstart

import numpy as np
from auto_stretch import apply_stretch, Stretch

image = np.array([[0.1, 0.25], [0.8, 0.3]], dtype=np.float64)

stretched = apply_stretch(image)
# or with custom parameters:
stretched = Stretch(target_bkg=0.25, shadows_clip=-1.25).stretch(image)

Input contract

• Input must be a 2D numpy array. 1D and 3D arrays raise ValueError.
• Input is coerced to float64 internally; the caller's array is never mutated.
• NaN pixels propagate through the stretch unchanged.
• Output is float64 with values clamped to [0, 1].

Parameters

Parameter	Default	Description
target_bkg	0.25	Target median brightness after stretch
shadows_clip	-1.25	Shadow clipping point in units of median absolute deviation below the median

The underlying algorithm follows the PixInsight Histogram Transformation STF method.

Dependencies

• Python >= 3.10
• numpy >= 1.20

Credit

Based on the PixInsight Screen Transfer Function (STF) algorithm developed by Pleiades Astrophoto.

License

MIT — see LICENSE.