Convert opencv image format to PIL image format?

Yes OpenCV is more robust and flexible and can perform most of the image processing routines which are available out there, So probably this filter can be done with OpenCV> However, there may not be a straightforward API for that.

Anyways, as far as the conversion of image format from OpenCV to PIL is concerned you may use Image.fromarray as:

import cv2
import numpy as np
from PIL import Image

img = cv2.imread("path/to/img.png")

# You may need to convert the color.
img = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
im_pil = Image.fromarray(img)

# For reversing the operation:
im_np = np.asarray(im_pil)

But you must keep in mind that, OpenCV follows BGR convention and PIL follows RGB color convention, so to keep the things consistent you may need to do use cv2.cvtColor() before conversion.