File size: 2,228 Bytes
fd9bd2c | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 | """Rotation utilities that preserve image content without artificial borders."""
import cv2
import numpy as np
import math
def rotate_image(img, angle, rotation_center=None, expand=False, border_mode=cv2.BORDER_CONSTANT, border_value=0):
"""Rotates an image (angle in degrees) and optionally expands to avoid cropping."""
h, w = img.shape[:2]
if rotation_center is None:
rotation_center = (w/2, h/2)
M = cv2.getRotationMatrix2D(rotation_center, angle, 1.0)
if expand:
abs_cos = abs(M[0, 0])
abs_sin = abs(M[0, 1])
wn = int(h * abs_sin + w * abs_cos)
hn = int(h * abs_cos + w * abs_sin)
M[0, 2] += wn/2 - rotation_center[0]
M[1, 2] += hn/2 - rotation_center[1]
else:
wn, hn = w, h
rotated = cv2.warpAffine(
img, M, (wn, hn), borderMode=border_mode, borderValue=border_value)
return rotated, M
def largest_rotated_rect(w, h, angle):
"""Compute the largest axis-aligned rectangle within a rotated rectangle."""
if w <= 0 or h <= 0:
return 0, 0
width_is_longer = w >= h
side_long, side_short = (w, h) if width_is_longer else (h, w)
sin_a, cos_a = abs(math.sin(angle)), abs(math.cos(angle))
if side_short <= 2.*sin_a*cos_a*side_long or abs(sin_a-cos_a) < 1e-10:
x = 0.5*side_short
wr, hr = (x/sin_a, x/cos_a) if width_is_longer else (x/cos_a, x/sin_a)
else:
cos_2a = cos_a*cos_a - sin_a*sin_a
wr, hr = (w*cos_a - h*sin_a)/cos_2a, (h*cos_a - w*sin_a)/cos_2a
return wr, hr
def rotate_image_crop_max_area(image, angle):
"""Rotate image and crop to the largest inscribed rectangle (no borders).
Args:
image: numpy array (OpenCV image)
angle: Rotation angle in degrees
Returns:
Rotated and cropped numpy array
"""
h, w = image.shape[:2]
rotated, _ = rotate_image(image, angle, expand=True)
wr, hr = largest_rotated_rect(w, h, math.radians(angle))
h_rot, w_rot = rotated.shape[:2]
y1 = h_rot//2 - int(hr/2)
y2 = y1 + int(hr)
x1 = w_rot//2 - int(wr/2)
x2 = x1 + int(wr)
return rotated[y1:y2, x1:x2]
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