AstroPrep · Preprocessor

Pick or capture a photo from your phone gallery. JPEG, PNG, HEIC supported.

Original

Output

idle

Estimated detections: 0 stars

Parameters

Auto crop

Detect the eyepiece field by luminance, crop to a square and mask the boundary to eliminate noise. 1 = on (default), 0 = off (process full frame).

Downsample

×

Process at 1/N resolution. Higher = faster, lower memory. Default 2× is good for 12 MP iPhone shots.

Background kernel

px

Median filter size for sky-glow estimation. Default 20.

Detection threshold

DN

DN above local background to enter detection. Default 20.

Min blob size

px

Real stars are large diffuse blobs, noise spikes are tiny. Default 4.

Max blob size

px

Discard very large blobs (clouds, glow, lens-flare). Default 2000.

Max compactness

Peak/area ratio. Real stars ≤ 6.0, noise spikes ≥ 10. Default 6.0.

Max colour CV

RGB coefficient of variation. Stars are neutral white; ISO noise is coloured. Default 0.5. Set to 1.0 to disable.

Glow σ

Gaussian profile sigma for accepted stars. Default 1.5 — smooths centroids for the source extractor. Set to 0 to disable.

Stretch

×

Brightness multiplier after normalisation. Default 3.0 — keeps faint stars visible without saturating the bright ones.

Background lift

DN

Output background grey level. Default 12 — small lift helps astrometry's source extractor pick its detection threshold.

Log