OpenCV Python：旋转图像而不裁剪边

Question

想象一下我有这些图像：

我希望左侧的图像像中间的图像一样旋转，而不是右侧的图像。 我如何使用 Python 和 OpenCV 做到这一点。 我查看了getRotationMatrix2D和warpAffine但有关它的示例将我的图像转换为正确的图像。

Answer 1

这是迄今为止我找到的旋转图像同时避免裁剪图像的最佳解决方案。

在 C++ 中的 OpenCV 中旋转图像而不进行裁剪

import cv2

def rotate_image(mat, angle):
    """
    Rotates an image (angle in degrees) and expands image to avoid cropping
    """

    height, width = mat.shape[:2] # image shape has 3 dimensions
    image_center = (width/2, height/2) # getRotationMatrix2D needs coordinates in reverse order (width, height) compared to shape

    rotation_mat = cv2.getRotationMatrix2D(image_center, angle, 1.)

    # rotation calculates the cos and sin, taking absolutes of those.
    abs_cos = abs(rotation_mat[0,0]) 
    abs_sin = abs(rotation_mat[0,1])

    # find the new width and height bounds
    bound_w = int(height * abs_sin + width * abs_cos)
    bound_h = int(height * abs_cos + width * abs_sin)

    # subtract old image center (bringing image back to origo) and adding the new image center coordinates
    rotation_mat[0, 2] += bound_w/2 - image_center[0]
    rotation_mat[1, 2] += bound_h/2 - image_center[1]

    # rotate image with the new bounds and translated rotation matrix
    rotated_mat = cv2.warpAffine(mat, rotation_mat, (bound_w, bound_h))
    return rotated_mat

当角度为 90*n 时，您可以添加检查以避免一些计算，但此函数将按原样适用于任何角度。

Answer 2

如果您只关心 90 度旋转 numpy 。 它更容易并且适用于opencv输入：

import numpy as np
rotated_image = np.rot90(im)

Answer 3

由于我不知道您的代码，我仍然猜想使用imutils.rotate_bound函数可以解决问题。 例如： rotate = imutils.rotate_bound(image, angle)

Answer 4

这是使用 cv2.rotate(frame,rotateCode = 1) 旋转图像帧并使用帧的 cv2.CAP_PROP_FRAME_WIDTH 和 cv2.CAP_PROP_FRAME_HEIGHT 重新缩放或调整大小的最简单方法。

import numpy as np
import cv2

cam = cv2.VideoCapture(2)

while(True):
    # Capture frame-by-frame
    cam.set(cv2.CAP_PROP_FRAME_WIDTH, 640) # You can change frame width by chaning number.

    cam.set(cv2.CAP_PROP_FRAME_HEIGHT, 480) # You can change frame height by chaning number.

    ret, frame = cam.read()

    new_frame=cv2.rotate(frame,rotateCode = 1) 

您可以输入 rotateCode= 0 或 1 或 2。取决于您的轮换。 它会给你 0 或 90 或 180 或 270 个角度

    # Display the resulting frame
    cv2.imshow('frame',new_frame)

    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

# When everything done, release the capture
cam.release()
cv2.destroyAllWindows()

希望对您有所帮助。

Answer 5

虽然这个问题是针对 CV2 提出的，但您可以使用 python 的本机图像库来做到这一点。

rotate_degrees = -90
img = Image.open(input_file_path)
img2 = img.rotate(rotate_degrees, expand=True)
img2.save(output_file_path)

如果您在旋转命令中省略expand=True ，您将得到一个看起来像 OP 右手照片的结果。

Answer 6

您也可以使用填充，即在图像的两侧添加边框，然后将其旋转以避免从原始图像中裁剪。

def rotate_im(image, angle)
    image_height = image.shape[0]
    image_width = image.shape[1]
    diagonal_square = (image_width*image_width) + (
        image_height* image_height
    )
    #
    diagonal = round(sqrt(diagonal_square))
    padding_top = round((diagonal-image_height) / 2)
    padding_bottom = round((diagonal-image_height) / 2)
    padding_right = round((diagonal-image_width) / 2)
    padding_left = round((diagonal-image_width) / 2)
    padded_image = cv2.copyMakeBorder(image,
                                      top=padding_top,
                                      bottom=padding_bottom,
                                      left=padding_left,
                                      right=padding_right,
                                      borderType=cv2.BORDER_CONSTANT,
                                      value=0
            )
    padded_height = padded_image.shape[0]
    padded_width = padded_image.shape[1]
    transform_matrix = cv2.getRotationMatrix2D(
                (padded_height/2,
                 padded_width/2), # center
                angle, # angle
      1.0) # scale
    rotated_image = cv2.warpAffine(padded_image,
                                   transform_matrix,
                                   (diagonal, diagonal),
                                   flags=cv2.INTER_LANCZOS4)
    return rotated_image

Answer 7

它很简单，不需要任何warpaffine或任何计算检查此代码

import numpy as np
from PIL import ImageGrab
import cv2

angle = -90
scale = 1.0

while True:
    img = ImageGrab.grab()
    img_np = np.array(img)
    frame = cv2.cvtColor(img_np, cv2.COLOR_BGR2RGB)
    new = cv2.rotate(frame,rotateCode = 0)# this is the line to rotate the image
    true = cv2.resize(new, (0,0), fx = 0.6, fy = 0.6) # with fxand fy u can control the size
    cv2.imshow('output', true)
    if cv2.waitKey(1) == 27:
        break


cv2.destroyAllWindows()

Answer 8

这是来自SciPy的ndimage.rotate的替代方法

相关文档

from scipy.ndimage import rotate as rotate_image

#rotation angle in degree
rotated_img1 = rotate_image(img,90)

rotated_img2 = rotate_image(img,-110)

rotated_img3 = rotate_image(img,-45)

# angles extending beyond 360 are calculated appropriately:
rotated_img4 = rotate_image(img,390)