OpenCV Python : rotate image without cropping sides
Solution 1
This is by far the best solution i have found for rotating images while avoiding cropping the image.
Rotate an image without cropping in OpenCV in C++
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
You can add checks to avoid some calculations when the angles are 90*n, but this function will work for any angle as is.
Solution 2
If you only care about 90 degree rotations numpy instead. It's much easier and works on opencv input:
import numpy as np
rotated_image = np.rot90(im)
Solution 3
As I don't know your code I still would guess that using the imutils.rotate_bound
function will solve the problem. E.g.: rotate = imutils.rotate_bound(image, angle)
Solution 4
This is the easiest way to rotate image frames by using cv2.rotate(frame,rotateCode = 1) and rescale or resizing by using cv2.CAP_PROP_FRAME_WIDTH and cv2.CAP_PROP_FRAME_HEIGHT of the frame.
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)
You can enter rotateCode= 0 or 1 or 2. Depends on your rotation. It's gonna give you 0 or 90 or 180 or 270 angles
# 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()
Hopefully, it with help you.
Solution 5
While this question was asked for CV2, you can do this with python's native image library.
rotate_degrees = -90
img = Image.open(input_file_path)
img2 = img.rotate(rotate_degrees, expand=True)
img2.save(output_file_path)
If you leave out expand=True
in the rotate command you will get a result that looks like OP's right hand photo.
Fosheus Badabu
Updated on July 09, 2022Comments
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Fosheus Badabu almost 2 years
Imagine I have these images :
I want the image from left to be rotated like the image of the middle, not the right one. How do I do this using Python and OpenCV. I looked at
getRotationMatrix2D
andwarpAffine
but the examples about it transform my image to the right one.