warp image arbitrarily (nonlinear)

image_warp.py

import numpy as np
import cv2

def remap_test(img_arr):
    H,W = img_arr.shape[0:2]
    map = np.mgrid[0:H,0:W]   # the map doesnt have to be same dims. as image size; it just declares what pixels in input image map to given output pixel
    map_x = map[1].astype(np.float32)  
    map_y = map[0].astype(np.float32)
#linear warp
    # for i in range(H):
    #     map_x[i,:]=np.arange(i,i+W,dtype=np.float32)
    for i in range(H):
        map_x[i,:]=map_x[i,:]+80*np.sin(2*3.14*float(i)/H)
    print(map)
    print(map_x,map_y)
    img_warped = cv2.remap(img_arr,map_x,map_y,cv2.INTER_LINEAR)
    cv2.imshow('post',img_warped)
    cv2.waitKey(0)


img_arr = cv2.imread('images/cat.jpg')
img_arr = cv2.cvtColor(img_arr,cv2.COLOR_BGR2GRAY)
cv2.imshow('pre',img_arr)
cv2.waitKey(0)
remap_test(img_arr)