Mirror/intercept
1
0
Fork 0
mirror of https://github.com/smittix/intercept.git synced 2026-04-25 07:10:00 -07:00
Code Issues Packages Projects Releases Wiki Activity

fix: Correct Scottie SSTV image slant by resyncing to mid-line sync pulse

Browse Source 
Scottie modes place their horizontal sync pulse between the Blue and Red
channels. The decoder was using a fixed offset to skip over it, so any
SDR clock error accumulated line-by-line and produced a visible diagonal
slant in the decoded image.

Fix: search for the actual 1200 Hz sync pulse in a ±10% window around
the expected position before decoding the Red channel, then align to the
real pulse. This resets accumulated clock drift on every scanline, the
same way Martin and Robot modes already handle their front-of-line sync.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
This commit is contained in:
Smittix
2026-02-19 09:54:28 +00:00
parent 17f6947648
commit 0dc40bbea3
1 changed files with 17 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

19
utils/sstv/image_decoder.py
View File

@@ -234,8 +234,23 @@ class SSTVImageDecoder:
# Scottie: separator between G and B
pos += self._porch_samples
else:
# Scottie: sync + porch between B and R
pos += self._sync_samples + self._porch_samples
# Scottie: sync + porch between B and R.
# Search for the actual sync pulse to correct for
# SDR clock drift — without this, any timing error
# accumulates line-by-line producing a visible slant.
search_margin = max(100, self._line_samples // 10)
sync_search_start = max(0, pos - search_margin)
sync_search_end = min(
len(self._buffer),
pos + self._sync_samples + search_margin,
)
sync_region = self._buffer[sync_search_start:sync_search_end]
sync_found = self._find_sync(sync_region)
if sync_found is not None:
pos = (sync_search_start + sync_found
+ self._sync_samples + self._porch_samples)
else:
pos += self._sync_samples + self._porch_samples
elif self._separator_samples > 0:
# Robot: separator + porch between channels
pos += self._separator_samples