一、函數簡介
# 圖片旋轉,不損失像素
getRotationMatrix2D函數
def rotate_bound(image, angle):
# grab the dimensions of the image and then determine the
# center
(h, w) = image.shape[:2]
(cX, cY) = (w // 2, h // 2)
# grab the rotation matrix (applying the negative of the
# angle to rotate clockwise), then grab the sine and cosine
# (i.e., the rotation components of the matrix)
# 這裏的第一個參數爲旋轉中心，第二個爲旋轉角度，第三個爲旋轉後的縮放因子
# 可以通過設置旋轉中心，縮放因子，以及窗口大小來防止旋轉後超出邊界的問題
M = cv2.getRotationMatrix2D((cX, cY), -angle, 1.0)
cos = np.abs(M[0, 0])
sin = np.abs(M[0, 1])
# compute the new bounding dimensions of the image
nW = int((h * sin) + (w * cos))
nH = int((h * cos) + (w * sin))
# adjust the rotation matrix to take into account translation
M[0, 2] += (nW / 2) - cX
M[1, 2] += (nH / 2) - cY
# perform the actual rotation and return the image
return cv2.warpAffine(image, M, (nW, nH)) # 第三個參數是輸出圖像的尺寸中心