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import cv2 as cv
import numpy as np

def twirl(img,xc,yc,alpha,r_max):
    height=img.shape[0]
    width=img.shape[1]
    transformed=np.copy(img)
    
    for x_prime in range(img.shape[0]):
        for y_prime in range(img.shape[1]):
            dx=x_prime-xc
            dy=y_prime-yc
            r=np.sqrt(dx**2+dy**2)
            beta=np.arctan(dy/dx)+alpha*((r_max-r)/r_max)
            print('hello')
            
            if r<r_max:
                x=xc+r*np.cos(beta)
                y=yc+r*np.cos(beta)
            
            if 0 <= x < height - 1 and 0 <= y < width - 1:
                j=int(x)
                k=int(y)
                # j1=j+1
                # k1=k+1
                
                a=abs(x-j)
                b=abs(y-k)
                
                transformed[x_prime,y_prime]=(1-b)*(1-a)*img[j,k]+(1-b)*a*img[j+1,k]+\
                    b*(1-a)*img[j,k+1]+b*a*img[j+1,k+1]
    return transformed
    
img=cv.imread('twirl.png')
xc = img.shape[0] // 2
yc= img.shape[1] // 2
r_max = xc- 10
alpha = np.deg2rad(90)
out=twirl(img,xc,yc,alpha,r_max)

cv.imshow("Output",out)
cv.waitKey(0)
cv.destroyAllWindows()

I'm trying to apply twirl effect using bilinear interpolation. My code is given here. It gives the following error on 28th line.
if 0 <= x < height - 1 and 0 <= y < width - 1:

UnboundLocalError: local variable 'x' referenced before assignment

I searched for the same kind of errors but it's not helping.

fairooz ahmed
  • 1
  • 1

2 Answers2

0

The problem is if the condition r < r_max is not satisfied, and as a result, the code skips the assignment of x and y. Try this instead:

import cv2 as cv
import numpy as np

def twirl(img, xc, yc, alpha, r_max):
    height = img.shape[0]
    width = img.shape[1]
    transformed = np.copy(img)
    
    for x_prime in range(img.shape[0]):
        for y_prime in range(img.shape[1]):
            dx = x_prime - xc
            dy = y_prime - yc
            r = np.sqrt(dx ** 2 + dy ** 2)
            beta = np.arctan(dy / dx) + alpha * ((r_max - r) / r_max)
            
            x = xc
            y = yc
            
            if r < r_max:
                x = xc + r * np.cos(beta)
                y = yc + r * np.sin(beta)
            
            if 0 <= x < height - 1 and 0 <= y < width - 1:
                j = int(x)
                k = int(y)
                
                a = abs(x - j)
                b = abs(y - k)
                
                transformed[x_prime, y_prime] = (1 - b) * (1 - a) * img[j, k] + (1 - b) * a * img[j + 1, k] + \
                    b * (1 - a) * img[j, k + 1] + b * a * img[j + 1, k + 1]
    
    return transformed

img = cv.imread('twirl.png')
xc = img.shape[0] // 2
yc = img.shape[1] // 2
r_max = xc - 10
alpha = np.deg2rad(90)
out = twirl(img, xc, yc, alpha, r_max)

cv.imshow("Output", out)
cv.waitKey(0)
cv.destroyAllWindows()
Phoenix
  • 1,343
  • 8
  • 10
0

The error happens when this if statement is False. You have to add else statement to set values for x and y variables or set some default values for them before if statement.

if r<r_max:
    x=xc+r*np.cos(beta)
    y=yc+r*np.cos(beta)
Bro From Space
  • 91
  • 8