constant displacement check

src/stitching_scanner.py

@@ -3,6 +3,7 @@ Stitching Scanner v2 - Simplified unified approach
 
 Same displacement-based stitching for both horizontal rows and vertical row transitions.
 No complex visual matching - just track displacement and append strips.
+Continuous alignment correction for gear slippage compensation.
 """
 
 import cv2
@@ -55,17 +56,19 @@ class StitchState:
 
 
 @dataclass
-class RowAlignmentOffset:
-    """Stores the alignment offset calculated at the start of each row"""
+class AlignmentOffset:
+    """Stores alignment offset for strip placement"""
     x_offset: float = 0.0
     y_offset: float = 0.0
     valid: bool = False
+    confidence: float = 0.0  # Phase correlation response
 
 
 class StitchingScanner:
     """
     Slide scanner using continuous stitching.
     Unified approach for horizontal and vertical movement.
+    Continuous alignment correction for gear slippage compensation.
     """
     
     def __init__(self, camera, motion_controller, autofocus_controller=None,
@@ -94,9 +97,12 @@ class StitchingScanner:
         self._displacement_since_append_x: float = 0.0
         self._displacement_since_append_y: float = 0.0
         
-        # Row alignment offset - calculated at the start of each row
-        self._row_alignment = RowAlignmentOffset()
-        self._is_first_strip_of_row: bool = True
+        # Cumulative alignment drift - tracks total correction applied
+        self._cumulative_align_x: float = 0.0
+        self._cumulative_align_y: float = 0.0
+        
+        # Last strip's alignment for continuity
+        self._last_strip_alignment = AlignmentOffset()
         
         self._thread: Optional[threading.Thread] = None
     
@@ -130,9 +136,29 @@ class StitchingScanner:
         prev_f = prev_f * window
         curr_f = curr_f * window
         
-        shift, _ = cv2.phaseCorrelate(prev_f, curr_f)
+        shift, response = cv2.phaseCorrelate(prev_f, curr_f)
         return shift
     
+    def _detect_displacement_with_confidence(self, prev_frame: np.ndarray,
+                                             curr_frame: np.ndarray) -> Tuple[float, float, float]:
+        """Detect displacement and return confidence (phase correlation response)."""
+        prev_gray = self._to_grayscale(prev_frame)
+        curr_gray = self._to_grayscale(curr_frame)
+        
+        if prev_gray.shape != curr_gray.shape:
+            return (0.0, 0.0, 0.0)
+        
+        prev_f = prev_gray.astype(np.float32)
+        curr_f = curr_gray.astype(np.float32)
+        
+        h, w = prev_gray.shape
+        window = cv2.createHanningWindow((w, h), cv2.CV_32F)
+        prev_f = prev_f * window
+        curr_f = curr_f * window
+        
+        shift, response = cv2.phaseCorrelate(prev_f, curr_f)
+        return (shift[0], shift[1], response)
+    
     def _detect_displacement_robust(self, prev_frame: np.ndarray,
                                    curr_frame: np.ndarray) -> Tuple[float, float]:
         dx, dy = self._detect_displacement(prev_frame, curr_frame)
@@ -146,76 +172,115 @@ class StitchingScanner:
         
         return (dx, dy)
     
-    def _detect_row_alignment(self, current_frame: np.ndarray, direction: ScanDirection) -> RowAlignmentOffset:
+    def _detect_strip_alignment(self, frame: np.ndarray, direction: ScanDirection,
+                                expected_x: int, expected_y: int) -> AlignmentOffset:
         """
-        Detect alignment offset at the start of a new row by comparing
-        the current frame with the overlapping region of the mosaic.
+        Detect alignment offset for a strip by comparing the current frame
+        with the expected overlap region of the mosaic.
         
-        This compensates for backlash in control gears that causes circular
-        motion instead of right angles when transitioning from vertical to horizontal.
+        This provides continuous correction for gear slippage during scanning.
+        
+        Args:
+            frame: Current camera frame
+            direction: Scan direction
+            expected_x: Expected X position in mosaic
+            expected_y: Expected Y position in mosaic
+        
+        Returns:
+            AlignmentOffset with X/Y correction needed
         """
-        offset = RowAlignmentOffset()
+        offset = AlignmentOffset()
         
         with self._mosaic_lock:
             if self.mosaic is None:
-                self.log("No mosaic for row alignment detection")
                 return offset
             
             mh, mw = self.mosaic.shape[:2]
-            fh, fw = current_frame.shape[:2]
+            fh, fw = frame.shape[:2]
             
-            # Determine where in the mosaic we expect to overlap
-            # For LEFT direction: we're at the right edge of the mosaic
-            # For RIGHT direction: we're at the left edge (but this is row 0, shouldn't need alignment)
+            # Clamp expected positions
+            expected_y = max(0, min(expected_y, mh - fh))
+            expected_x = max(0, min(expected_x, mw - fw))
             
-            if direction == ScanDirection.LEFT:
-                # We're starting from the right side, moving left
-                # The current frame should overlap with the right edge of the mosaic
-                # Extract the rightmost portion of the mosaic that should overlap
+            if direction == ScanDirection.RIGHT:
+                # We're appending to the right
+                # Compare left portion of frame with right edge of mosaic
+                overlap_width = min(fw // 2, mw - expected_x, 200)  # Use up to 200px overlap
                 
-                # The overlap region is at the bottom-right of the mosaic
-                # Current Y position in mosaic
-                y_pos = int(self.state.current_y)
-                y_pos = max(0, min(y_pos, mh - fh))
+                if overlap_width < 30:
+                    return offset
                 
-                # Extract overlap region from mosaic (right edge)
-                overlap_width = min(fw, mw)
-                mosaic_region = self.mosaic[y_pos:y_pos + fh, mw - overlap_width:mw]
-                frame_region = current_frame[:, :overlap_width]
+                # Extract regions
+                mosaic_region = self.mosaic[expected_y:expected_y + fh, mw - overlap_width:mw]
+                frame_region = frame[:, :overlap_width]
                 
-            else:  # RIGHT direction
-                # We're starting from the left side, moving right
-                # Current Y position in mosaic
-                y_pos = int(self.state.current_y)
-                y_pos = max(0, min(y_pos, mh - fh))
+            elif direction == ScanDirection.LEFT:
+                # We're placing within existing mosaic, moving left
+                # Compare right portion of frame with mosaic at expected position
+                overlap_width = min(fw // 2, mw - expected_x, 200)
                 
-                # Extract overlap region from mosaic (left edge)
-                overlap_width = min(fw, mw)
-                mosaic_region = self.mosaic[y_pos:y_pos + fh, :overlap_width]
-                frame_region = current_frame[:, :overlap_width]
+                if overlap_width < 30:
+                    return offset
+                
+                # The frame's right edge should align with mosaic at expected_x + fw
+                mosaic_x_end = min(expected_x + fw, mw)
+                mosaic_x_start = max(mosaic_x_end - overlap_width, 0)
+                actual_overlap = mosaic_x_end - mosaic_x_start
+                
+                if actual_overlap < 30:
+                    return offset
+                
+                mosaic_region = self.mosaic[expected_y:expected_y + fh, mosaic_x_start:mosaic_x_end]
+                frame_region = frame[:, fw - actual_overlap:]
+                
+            elif direction == ScanDirection.DOWN:
+                # We're appending below
+                # Compare top portion of frame with bottom edge of mosaic
+                overlap_height = min(fh // 2, mh - expected_y, 200)
+                
+                if overlap_height < 30:
+                    return offset
+                
+                mosaic_region = self.mosaic[mh - overlap_height:mh, expected_x:expected_x + fw]
+                frame_region = frame[:overlap_height, :]
+                
+            else:  # UP
+                # Compare bottom portion of frame with top edge of mosaic
+                overlap_height = min(fh // 2, expected_y, 200)
+                
+                if overlap_height < 30:
+                    return offset
+                
+                mosaic_region = self.mosaic[:overlap_height, expected_x:expected_x + fw]
+                frame_region = frame[fh - overlap_height:, :]
             
             # Ensure regions have the same size
             min_h = min(mosaic_region.shape[0], frame_region.shape[0])
             min_w = min(mosaic_region.shape[1], frame_region.shape[1])
             
-            if min_h < 50 or min_w < 50:
-                self.log(f"Overlap region too small for alignment: {min_w}x{min_h}")
+            if min_h < 30 or min_w < 30:
+                self.log(f"Strip alignment: overlap too small ({min_w}x{min_h})")
                 return offset
             
             mosaic_region = mosaic_region[:min_h, :min_w]
             frame_region = frame_region[:min_h, :min_w]
             
-            # Detect displacement between mosaic region and current frame
-            dx, dy = self._detect_displacement_robust(mosaic_region, frame_region)
+            # Detect displacement with confidence
+            dx, dy, confidence = self._detect_displacement_with_confidence(mosaic_region, frame_region)
+            
+            # Sanity check - reject large displacements
+            max_adjust = 50  # Max pixels to adjust
+            if abs(dx) > max_adjust or abs(dy) > max_adjust:
+                self.log(f"Strip alignment: displacement too large ({dx:.1f}, {dy:.1f}), ignoring")
+                return offset
             
             offset.x_offset = dx
             offset.y_offset = dy
-            offset.valid = True
+            offset.confidence = confidence
+            offset.valid = confidence > 0.1  # Require minimum confidence
             
-            self.log(f"=== Row Alignment Detection ===")
-            self.log(f"  Direction: {direction.value}")
-            self.log(f"  Mosaic region: {mosaic_region.shape[1]}x{mosaic_region.shape[0]} at Y={y_pos}")
-            self.log(f"  Detected offset: X={dx:.1f}, Y={dy:.1f}")
+            if offset.valid:
+                self.log(f"  Strip alignment: X={dx:.1f}, Y={dy:.1f}, conf={confidence:.3f}")
         
         return offset
     
@@ -231,9 +296,10 @@ class StitchingScanner:
         self._displacement_since_append_x = 0.0
         self._displacement_since_append_y = 0.0
         
-        # Reset row alignment for first row (no alignment needed)
-        self._row_alignment = RowAlignmentOffset()
-        self._is_first_strip_of_row = False  # First row doesn't need alignment
+        # Reset cumulative alignment
+        self._cumulative_align_x = 0.0
+        self._cumulative_align_y = 0.0
+        self._last_strip_alignment = AlignmentOffset()
         
         with self._state_lock:
             h, w = frame.shape[:2]
@@ -262,8 +328,8 @@ class StitchingScanner:
             append_right: True to append to right, False to append left
             x_offset: X position for left-append mode
             y_offset: Y position in the mosaic
-            alignment_x: Additional X alignment offset (from row alignment detection)
-            alignment_y: Additional Y alignment offset (from row alignment detection)
+            alignment_x: Additional X alignment offset (from strip alignment detection)
+            alignment_y: Additional Y alignment offset (from strip alignment detection)
         """
         h_base, w_base = base.shape[:2]
         h_strip, w_strip = strip.shape[:2]
@@ -310,13 +376,12 @@ class StitchingScanner:
             if x_offset is None:
                 x_offset = 0
             
-            # Apply alignment offsets (detected at start of row)
+            # Apply alignment offsets (continuous correction)
             x_offset = x_offset + int(round(alignment_x))
             y_offset = y_offset - int(round(alignment_y))
             
             # Clamp x_offset to valid range
-            # x_offset = max(0, min(x_offset, w_base - blend_w))
-            x_offset = 0 - min(x_offset, w_base)
+            x_offset = max(0, min(x_offset, w_base - blend_w))
             
             # Handle strip cropping if y_offset is negative (strip protrudes above frame)
             strip_y_start = 0  # How much to crop from top of strip
@@ -343,6 +408,7 @@ class StitchingScanner:
             self.log(f"  base: {w_base}x{h_base}, strip: {w_strip}x{h_strip}")
             self.log(f"  x_offset: {x_offset}, y_offset: {y_offset}, blend_w: {blend_w}")
             self.log(f"  alignment: X={alignment_x:.1f}, Y={alignment_y:.1f}")
+            self.log(f"  cumulative: X={self._cumulative_align_x:.1f}, Y={self._cumulative_align_y:.1f}")
             self.log(f"  Strip crop: rows [{strip_y_start}:{strip_y_end}] -> height {h_cropped}")
             
             # Result is same size as base (no expansion when going left)
@@ -426,12 +492,15 @@ class StitchingScanner:
 
     def _blend_vertical_at_x(self, base: np.ndarray, strip: np.ndarray,
                              blend_height: int, append_below: bool,
-                         x_off: int = 0) -> np.ndarray:
+                             x_off: int = 0,
+                             alignment_x: float = 0.0, alignment_y: float = 0.0) -> np.ndarray:
         h_base, w_base = base.shape[:2]
         h_strip, w_strip = strip.shape[:2]
         
-        # Clamp x_offset to valid range
+        # Apply alignment offset for X position
         x_offset = max(0, w_base - self.state.mosaic_init_width)
+        x_offset = x_offset + int(round(alignment_x))
+        x_offset = max(0, min(x_offset, w_base - w_strip)) if w_strip < w_base else 0
         
         # Create full-width strip with strip placed at x_offset
         full_strip = np.zeros((h_strip, w_base, 3), dtype=np.uint8)
@@ -439,16 +508,16 @@ class StitchingScanner:
         copy_width = min(w_strip, available_width)
         full_strip[:, x_offset:x_offset + copy_width] = strip[:, :copy_width]
         
+        self.log(f"=== _blend_vertical_at_x ===")
+        self.log(f"  base: {w_base}x{h_base}, strip: {w_strip}x{h_strip}")
+        self.log(f"  x_offset: {x_offset}, alignment: X={alignment_x:.1f}, Y={alignment_y:.1f}")
+        
         # Early exit: no blending possible
         if blend_height <= 0 or blend_height >= h_strip:
             if append_below:
                 return np.vstack([base, full_strip])
             return np.vstack([full_strip, base])
         
-        # Height mismatch shouldn't happen with full_strip, but safety check
-        if w_strip > w_base:
-            self.log(f"Warning: strip wider than base ({w_strip} > {w_base})")
-        
         blend_h = min(blend_height, h_strip, h_base)
         
         if append_below:
@@ -523,7 +592,7 @@ class StitchingScanner:
             return result
     
     def _append_strip(self, frame: np.ndarray, direction: ScanDirection):
-        """Append strip to mosaic based on accumulated displacement."""
+        """Append strip to mosaic based on accumulated displacement with continuous alignment."""
         BLEND_WIDTH = 10
         SAFETY_MARGIN = 2
         
@@ -537,9 +606,22 @@ class StitchingScanner:
             dx = abs(self._displacement_since_append_x)
             dy = abs(self._displacement_since_append_y)
             
-            # Get alignment offsets for this row
-            align_x = self._row_alignment.x_offset if self._row_alignment.valid else 0.0
-            align_y = self._row_alignment.y_offset if self._row_alignment.valid else 0.0
+            # Calculate expected position for alignment detection
+            expected_x = int(self.state.current_x + self._cumulative_align_x)
+            expected_y = int(self.state.current_y + self._cumulative_align_y)
+            
+            # Detect alignment for this strip
+            alignment = self._detect_strip_alignment(frame, direction, expected_x, expected_y)
+            
+            if alignment.valid:
+                # Update cumulative alignment
+                self._cumulative_align_x += alignment.x_offset
+                self._cumulative_align_y += alignment.y_offset
+                self._last_strip_alignment = alignment
+            
+            # Get total alignment offsets
+            align_x = self._cumulative_align_x
+            align_y = self._cumulative_align_y
             
             if direction in [ScanDirection.RIGHT, ScanDirection.LEFT]:
                 append_width = round(dx) + SAFETY_MARGIN
@@ -584,14 +666,18 @@ class StitchingScanner:
                 
                 if direction == ScanDirection.DOWN:
                     strip_end = min(h, append_height + BLEND_WIDTH)
-                    new_strip = frame[:strip_end:, :]
+                    new_strip = frame[:strip_end, :]
                     self.mosaic = self._blend_vertical_at_x(
-                        self.mosaic, new_strip, BLEND_WIDTH, append_below=False, x_off=int(self.state.current_x))
+                        self.mosaic, new_strip, BLEND_WIDTH, append_below=False, 
+                        x_off=int(self.state.current_x),
+                        alignment_x=align_x, alignment_y=align_y)
                 else:
                     strip_start = max(0, h - append_height - BLEND_WIDTH)
-                    new_strip = frame[:strip_start, :]
+                    new_strip = frame[strip_start:, :]
                     self.mosaic = self._blend_vertical_at_x(
-                        self.mosaic, new_strip, BLEND_WIDTH, append_below=True, x_off=int(self.state.current_x))
+                        self.mosaic, new_strip, BLEND_WIDTH, append_below=True, 
+                        x_off=int(self.state.current_x),
+                        alignment_x=align_x, alignment_y=align_y)
                 
                 self._displacement_since_append_x = 0.0
                 self._displacement_since_append_y = fractional_remainder
@@ -628,8 +714,11 @@ class StitchingScanner:
         self._prev_frame = None
         self._displacement_since_append_x = 0.0
         self._displacement_since_append_y = 0.0
-        self._row_alignment = RowAlignmentOffset()
-        self._is_first_strip_of_row = False  # First row doesn't need alignment
+        
+        # Reset cumulative alignment
+        self._cumulative_align_x = 0.0
+        self._cumulative_align_y = 0.0
+        self._last_strip_alignment = AlignmentOffset()
         
         self._thread = threading.Thread(target=self._scan_loop, daemon=True)
         self._thread.start()
@@ -680,26 +769,13 @@ class StitchingScanner:
                     self.state.total_rows = row + 1
                 
                 self.log(f"=== Row {row + 1} ===")
+                self.log(f"Cumulative alignment at row start: X={self._cumulative_align_x:.1f}, Y={self._cumulative_align_y:.1f}")
                 
                 # Serpentine: even rows right, odd rows left
                 h_direction = ScanDirection.RIGHT if row % 2 == 0 else ScanDirection.LEFT
                 
-                # For rows after the first, detect alignment at the start
-                if row > 0:
-                    self._is_first_strip_of_row = True
-                    frame = self._capture_frame()
-                    self._row_alignment = self._detect_row_alignment(frame, h_direction)
-                    self.log(f"Row {row + 1} alignment: X={self._row_alignment.x_offset:.1f}, Y={self._row_alignment.y_offset:.1f}")
-                else:
-                    # First row - no alignment needed
-                    self._row_alignment = RowAlignmentOffset()
-                    self._is_first_strip_of_row = False
-                
                 stop_reason = self._scan_direction(h_direction)
                 
-                # After first strip is appended, clear the flag
-                self._is_first_strip_of_row = False
-                
                 if not self.running:
                     break
                 
@@ -716,6 +792,7 @@ class StitchingScanner:
                 row += 1
             
             self.log(f"Scan complete! Final: {self.state.mosaic_width}x{self.state.mosaic_height}")
+            self.log(f"Final cumulative alignment: X={self._cumulative_align_x:.1f}, Y={self._cumulative_align_y:.1f}")
             
         except Exception as e:
             self.log(f"Scan error: {e}")
@@ -773,7 +850,7 @@ class StitchingScanner:
                 break
 
             if self.state.current_x >= 0 and direction == ScanDirection.LEFT:
-                self.log(f"Max dimension reached ({self.config.max_mosaic_width}px)")
+                self.log(f"Returned to start ({self.config.max_mosaic_width}px)")
                 self.log(f"Current X offset ({self.state.current_x}px) total_x ({total_x}px)")
                 stop_reason = 'max_dim'
                 break
@@ -799,7 +876,6 @@ class StitchingScanner:
             total_x += dx
             with self._state_lock:
                 self.state.current_x += dx
-            self.log(f"Current X offset ({self.state.current_x}px)")
             
             with self._state_lock:
                 self.state.cumulative_x = self._displacement_since_append_x
@@ -818,11 +894,11 @@ class StitchingScanner:
             else:
                 no_movement_count = 0
             
-            # Append when threshold reached
+            # Append when threshold reached (with continuous alignment)
             disp = abs(self._displacement_since_append_x) if direction in [ScanDirection.RIGHT, ScanDirection.LEFT] else abs(self._displacement_since_append_y)
             if disp >= threshold_pixels:
                 self._append_strip(curr_frame, direction)
-                self.log(f"Appended {disp:.1f}px, mosaic: {self.state.mosaic_width}x{self.state.mosaic_height}")
+                self.log(f"Appended {disp:.1f}px, mosaic: {self.state.mosaic_width}x{self.state.mosaic_height}, align: ({self._cumulative_align_x:.1f}, {self._cumulative_align_y:.1f})")
             
             self._prev_frame = curr_frame.copy()
             
@@ -837,9 +913,10 @@ class StitchingScanner:
     def _move_to_next_row(self) -> bool:
         """
         Move down to next row using displacement-based stitching.
-        Same approach as horizontal scanning.
+        Same approach as horizontal scanning with continuous alignment.
         """
         self.log("Moving to next row...")
+        self.log(f"Alignment before row transition: X={self._cumulative_align_x:.1f}, Y={self._cumulative_align_y:.1f}")
         
         frame = self._capture_frame()
         h, w = frame.shape[:2]
@@ -895,14 +972,16 @@ class StitchingScanner:
                 else:
                     no_movement_count = 0
                 
-                # Append strip when threshold reached
+                # Append strip when threshold reached (with continuous alignment)
                 if abs(self._displacement_since_append_y) >= threshold_pixels:
                     self._append_strip(curr_frame, ScanDirection.DOWN)
-                    self.log(f"  Row transition: appended, total Y: {abs(total_y):.1f}px")
+                    self.log(f"  Row transition: appended, total Y: {abs(total_y):.1f}px, align: ({self._cumulative_align_x:.1f}, {self._cumulative_align_y:.1f})")
                 
                 # Done when we've moved enough
                 if abs(total_y) >= target_displacement:
                     self.log(f"Row transition complete: {abs(total_y):.1f}px")
+                    self.log(f"Alignment after row transition: X={self._cumulative_align_x:.1f}, Y={self._cumulative_align_y:.1f}")
+                    
                     with self._state_lock:
                         self.state.current_y = 0
                     self.motion.send_command('s')
@@ -951,6 +1030,19 @@ class StitchingScanner:
                 append_count=self.state.append_count
             )
     
+    def get_alignment_state(self) -> dict:
+        """Get current alignment correction state."""
+        return {
+            'cumulative_x': self._cumulative_align_x,
+            'cumulative_y': self._cumulative_align_y,
+            'last_alignment': {
+                'x': self._last_strip_alignment.x_offset,
+                'y': self._last_strip_alignment.y_offset,
+                'confidence': self._last_strip_alignment.confidence,
+                'valid': self._last_strip_alignment.valid
+            }
+        }
+    
     def get_mosaic(self) -> Optional[np.ndarray]:
         with self._mosaic_lock:
             if self.mosaic is not None:
@@ -1006,6 +1098,8 @@ class StitchingScanner:
             'y_moved': 0.0,
             'mosaic_before': (0, 0),
             'mosaic_after': (0, 0),
+            'alignment_before': (0.0, 0.0),
+            'alignment_after': (0.0, 0.0),
             'error': None
         }
         
@@ -1017,6 +1111,7 @@ class StitchingScanner:
                 self._init_mosaic(frame)
             
             results['mosaic_before'] = (self.state.mosaic_width, self.state.mosaic_height)
+            results['alignment_before'] = (self._cumulative_align_x, self._cumulative_align_y)
             
             with self._state_lock:
                 self.state.cumulative_y = 0.0
@@ -1028,8 +1123,10 @@ class StitchingScanner:
             results['success'] = success
             results['y_moved'] = self.state.cumulative_y
             results['mosaic_after'] = (self.state.mosaic_width, self.state.mosaic_height)
+            results['alignment_after'] = (self._cumulative_align_x, self._cumulative_align_y)
             
             self.log(f"Row transition: {'SUCCESS' if success else 'FAILED'}, Y: {results['y_moved']:.1f}px")
+            self.log(f"Alignment change: ({results['alignment_before'][0]:.1f}, {results['alignment_before'][1]:.1f}) -> ({results['alignment_after'][0]:.1f}, {results['alignment_after'][1]:.1f})")
             
         except Exception as e:
             results['error'] = str(e)
@@ -1046,6 +1143,8 @@ class StitchingScanner:
             'appends': 0,
             'mosaic_before': (0, 0),
             'mosaic_after': (0, 0),
+            'alignment_before': (0.0, 0.0),
+            'alignment_after': (0.0, 0.0),
             'error': None
         }
         
@@ -1057,6 +1156,7 @@ class StitchingScanner:
                 self._init_mosaic(frame)
             
             results['mosaic_before'] = (self.state.mosaic_width, self.state.mosaic_height)
+            results['alignment_before'] = (self._cumulative_align_x, self._cumulative_align_y)
             appends_before = self.state.append_count
             
             self.motion.set_speed(self.config.scan_speed_index)
@@ -1064,13 +1164,6 @@ class StitchingScanner:
             
             self.running = True
             scan_dir = ScanDirection.RIGHT if direction == 'right' else ScanDirection.LEFT
-            
-            # Test row alignment detection if not first row
-            if self.state.current_row > 0 or self.mosaic is not None:
-                frame = self._capture_frame()
-                self._row_alignment = self._detect_row_alignment(frame, scan_dir)
-                self.log(f"Test row alignment: X={self._row_alignment.x_offset:.1f}, Y={self._row_alignment.y_offset:.1f}")
-            
             stop_reason = self._scan_direction(scan_dir)
             self.running = False
             
@@ -1078,6 +1171,9 @@ class StitchingScanner:
             results['stop_reason'] = stop_reason
             results['appends'] = self.state.append_count - appends_before
             results['mosaic_after'] = (self.state.mosaic_width, self.state.mosaic_height)
+            results['alignment_after'] = (self._cumulative_align_x, self._cumulative_align_y)
+            
+            self.log(f"Alignment change: ({results['alignment_before'][0]:.1f}, {results['alignment_before'][1]:.1f}) -> ({results['alignment_after'][0]:.1f}, {results['alignment_after'][1]:.1f})")
             
         except Exception as e:
             results['error'] = str(e)
@@ -1085,17 +1181,18 @@ class StitchingScanner:
         
         return results
     
-    def test_row_alignment(self, direction: str = 'left') -> dict:
-        """Test row alignment detection without scanning."""
+    def test_strip_alignment(self) -> dict:
+        """Test strip alignment detection at current position."""
         results = {
             'success': False,
             'x_offset': 0.0,
             'y_offset': 0.0,
+            'confidence': 0.0,
             'error': None
         }
         
         try:
-            self.log(f"Testing row alignment detection ({direction})...")
+            self.log("Testing strip alignment detection...")
             
             if self.mosaic is None:
                 self.log("No mosaic - initializing...")
@@ -1103,14 +1200,20 @@ class StitchingScanner:
                 self._init_mosaic(frame)
             
             frame = self._capture_frame()
-            scan_dir = ScanDirection.LEFT if direction == 'left' else ScanDirection.RIGHT
-            alignment = self._detect_row_alignment(frame, scan_dir)
+            expected_x = int(self.state.current_x + self._cumulative_align_x)
+            expected_y = int(self.state.current_y + self._cumulative_align_y)
             
+            # Test for both directions
+            for direction in [ScanDirection.RIGHT, ScanDirection.LEFT]:
+                alignment = self._detect_strip_alignment(frame, direction, expected_x, expected_y)
+                self.log(f"  {direction.value}: valid={alignment.valid}, X={alignment.x_offset:.1f}, Y={alignment.y_offset:.1f}, conf={alignment.confidence:.3f}")
+            
+            # Return RIGHT direction result
+            alignment = self._detect_strip_alignment(frame, ScanDirection.RIGHT, expected_x, expected_y)
             results['success'] = alignment.valid
             results['x_offset'] = alignment.x_offset
             results['y_offset'] = alignment.y_offset
-            
-            self.log(f"Alignment result: valid={alignment.valid}, X={alignment.x_offset:.1f}, Y={alignment.y_offset:.1f}")
+            results['confidence'] = alignment.confidence
             
         except Exception as e:
             results['error'] = str(e)
@@ -1118,6 +1221,13 @@ class StitchingScanner:
         
         return results
     
+    def reset_alignment(self):
+        """Reset cumulative alignment to zero."""
+        self._cumulative_align_x = 0.0
+        self._cumulative_align_y = 0.0
+        self._last_strip_alignment = AlignmentOffset()
+        self.log("Alignment reset to (0, 0)")
+    
     def get_memory_estimate(self) -> dict:
         current_bytes = self.mosaic.nbytes if self.mosaic is not None else 0
         max_bytes = self.config.max_mosaic_width * self.config.max_mosaic_height * 3