From bb092364afce5a79da686fdb7fbdfb4d2f6fb83a Mon Sep 17 00:00:00 2001
From: Robert Sachunsky <sachunsky@informatik.uni-leipzig.de>
Date: Fri, 24 Apr 2026 15:22:42 +0200
Subject: [PATCH] =?UTF-8?q?get=5Fslopes=5Fand=5Fdeskew=5Fnew=5Flight2:=20e?=
 =?UTF-8?q?stimate=20slopes=20here,=20too=E2=80=A6?=
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extract slopes from minimal bounding rectangles of textlines,
using heuristics on aspect ratios, lengths and angles
---
 src/eynollah/eynollah.py      |  7 ++++++-
 src/eynollah/utils/contour.py | 28 ++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/src/eynollah/eynollah.py b/src/eynollah/eynollah.py
index 5432b52..a659922 100644
--- a/src/eynollah/eynollah.py
+++ b/src/eynollah/eynollah.py
@@ -56,6 +56,7 @@ from .utils.contour import (
     dilate_textregion_contours,
     dilate_textline_contours,
     match_deskewed_contours,
+    estimate_skew_contours,
     polygon2contour,
     contour2polygon,
     join_polygons,
@@ -1007,7 +1008,11 @@ class Eynollah:
                 [w_h_textlines[ind] for ind in indexes_in])
 
             all_found_textline_polygons.append(textlines_in) #[::-1])
-            slopes.append(slope_deskew)
+
+            try:
+                slopes.append(estimate_skew_contours(textlines_in))
+            except ValueError:
+                slopes.append(slope_deskew)
 
         return all_found_textline_polygons, slopes
 
diff --git a/src/eynollah/utils/contour.py b/src/eynollah/utils/contour.py
index 4307409..07f89c9 100644
--- a/src/eynollah/utils/contour.py
+++ b/src/eynollah/utils/contour.py
@@ -396,6 +396,34 @@ def match_deskewed_contours(slope_deskew, contours_o, contours_d, shape_o, shape
     invsort_o = np.argsort(sort_o)
     return contours_d_ordered[invsort_o]
 
+def estimate_skew_contours(contours):
+    if not len(contours):
+        raise ValueError("not enough contours")
+    _, size_in, angle_in = zip(*map(cv2.minAreaRect, contours))
+    w_in, h_in = np.array(size_in).T
+    angle_in = np.array(angle_in)
+    transposed = h_in > w_in
+    # print("transposed", transposed, angle_in)
+    w_in[transposed], h_in[transposed] = h_in[transposed], w_in[transposed]
+    angle_in[transposed] -= 90
+    usable = w_in > 3 * h_in
+    # print("usable aspect", w_in / h_in, usable, angle_in[usable])
+    if not np.any(usable):
+        raise ValueError("not enough contours with high aspect ratio")
+    w_avg = np.median(w_in[usable])
+    w_dev = w_in[usable] / w_avg
+    usable[usable] = (0.67 <= w_dev) & (w_dev <= 1.33)
+    # print("usable width", usable, w_in[usable], angle_in[usable])
+    if not np.any(usable):
+        raise ValueError("not enough contours with consistent length")
+    angle_avg = np.median(angle_in[usable])
+    angle_dev = np.abs(angle_in[usable] - angle_avg)
+    usable[usable] = (angle_dev <= 2 * np.median(angle_dev))
+    # print("usable angle", usable, angle_in[usable], np.mean(angle_in[usable]))
+    if not np.any(usable):
+        raise ValueError("not enough contours with consistent angle")
+    return np.mean(angle_in[usable])
+
 def contour2polygon(contour: Union[np.ndarray, Sequence[Sequence[Sequence[Number]]]], dilate=0):
     polygon = Polygon([point[0] for point in contour])
     if dilate: