fix multi-level deskewing:

- angle already applied must be sum of angle applied on parent level
  and on current level
- not all image features are monotonic
  - some do propagate through all hierarchy levels:
    binarized, grayscale_normalized, despeckled
  - some must be treated level-local (to make sense and allow for
    relative coordinate consistency):
    deskewed, rotated-90, rotated-180, rotated-270, dewarped

ocrd/ocrd/workspace.py

@@ -616,12 +616,12 @@ def image_from_segment(self, segment, parent_image, parent_coords,
             orientation = orientation - (orientation % 90)
             skew = (angle % 360) - orientation
             skew = 180 - (180 - skew) % 360 # map to [-45,45]
-            segment_coords['angle'] = parent_coords['angle'] # nothing applied yet (depends on filters)
             log.debug("segment '%s' has orientation=%d skew=%.2f",
                       segment.id, orientation, skew)
         else:
             orientation = 0
             skew = 0
+        segment_coords['angle'] = parent_coords['angle'] # nothing applied yet (depends on filters)
 
         if (orientation and
             not 'rotated-%d' % orientation in feature_filter.split(',')):
@@ -638,7 +638,7 @@ def image_from_segment(self, segment, parent_image, parent_coords,
                           0.5 * segment_xywh['h']]))
             segment_xywh['w'], segment_xywh['h'] = adjust_canvas_to_transposition(
                 [segment_xywh['w'], segment_xywh['h']], transposition)
-            segment_coords['angle'] = orientation
+            segment_coords['angle'] += orientation
         if (skew and
             not 'deskewed' in feature_filter.split(',')):
             # Rotate around center in affine coordinate transform:
@@ -650,9 +650,13 @@ def image_from_segment(self, segment, parent_image, parent_coords,
                           0.5 * segment_xywh['h']]))
             segment_coords['angle'] += skew
 
-        # initialize AlternativeImage@comments classes from parent:
-        segment_coords['features'] = parent_coords['features'] + ',cropped'
-
+        # initialize AlternativeImage@comments classes from parent, except
+        # for those operations that can apply on multiple hierarchy levels:
+        segment_coords['features'] = ','.join(
+            [feature for feature in parent_coords['features'].split(',')
+             if feature in ['binarized', 'grayscale_normalized',
+                            'despeckled', 'dewarped']])
+
         alternative_image = None
         alternative_images = segment.get_AlternativeImage()
         if alternative_images: