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get_slopes_and_deskew_new_light2: avoid +/- 90° cancellation…

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in `estimate_skew_contours()`, distinguish between angle stats
scattering around <45° vs >45°: in the latter case, use modulo
180° for averages - to avoid cancelling out +90° with -90°
This commit is contained in:
Robert Sachunsky 2026-05-04 15:52:07 +02:00
parent 29bb55ceff
commit 934ac90e92
1 changed files with 26 additions and 6 deletions
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32
src/eynollah/utils/contour.py
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@ -402,27 +402,47 @@ def estimate_skew_contours(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)
# 1. depending on how contours are oriented,
# and where they start, minAreaRect can present
# either side as width or height; so we first
# need to normalise
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
# 2. now we look at aspect ratio: too short
# textlines do not yield reliable angles
usable = w_in > 2.5 * 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")
# 3. next, get rid of outliers regarding length
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])
# print("usable length", w_in[usable] / w_avg, 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)
if np.count_nonzero(usable) == 1:
return angle_in[usable]
# 4. there is no way to distinguish between +90 and -89.9 here,
# so map to [0,180] when calculating averages, then map back to [-90,90]
# (we don't want -90 and +89 to average zero, or +1 and +179 to average 90)
angles = angle_in[usable]
if transposed := np.median(np.abs(angles)) >= 45:
angles %= 180
angle_avg = np.median(angles)
angle_dev = np.abs(angles - angle_avg)
usable[usable] = (angle_dev <= 2 * np.median(angle_dev))
# print("usable angle", usable, angle_in[usable], np.mean(angle_in[usable]))
# print("usable angle", usable, angle_in[usable])
if not np.any(usable):
raise ValueError("not enough contours with consistent angle")
return np.mean(angle_in[usable])
if transposed:
angle = 90 - (90 - np.mean(angle_in[usable] % 180)) % 180
else:
angle = np.mean(angle_in[usable])
# print("mean angle", angle)
return angle
def contour2polygon(contour: Union[np.ndarray, Sequence[Sequence[Sequence[Number]]]], dilate=0):
polygon = Polygon([point[0] for point in contour])