Fix wrong VIS codes for PD90 (96→99), PD120 (93→95), PD180 (95→97),
PD240 (113→96), and ScottieDX (55→76). This caused PD180 to be detected
as PD90 and PD120 to fail entirely.
Replace batch Goertzel pixel decoding with analytic signal (Hilbert
transform) FM demodulation. The Goertzel approach used 96-sample windows
with ~500 Hz resolution — wider than the 800 Hz pixel frequency range —
making accurate pixel decoding impossible for fast modes like Martin2
and Scottie2. The Hilbert method computes per-sample instantaneous
frequency, matching the approach used by QSSTV and other professional
SSTV decoders.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Tolerate intermittent ambiguous windows during leader detection (up to
3 consecutive misses), use energy-based break detection when tone
classification fails at leader-break boundary, and add single-bit VIS
error correction for parity-bit and data-bit corruption on noisy HF.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
slowrx is a GTK GUI app that doesn't support CLI usage, so the SSTV
decoder was silently failing. This replaces it with a pure Python
implementation using numpy and Pillow that supports Robot36/72,
Martin1/2, Scottie1/2, and PD120/180 modes via VIS header auto-detection.
Key implementation details:
- Generalized Goertzel (DTFT) for exact-frequency tone detection
- Vectorized batch Goertzel for real-time pixel decoding performance
- Overlapping analysis windows for short-window frequency estimation
- VIS header detection state machine with parity validation
- Per-line sync re-synchronization for drift tolerance
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
