Rotating an Image using own algorithm in python

Question

For an uni assignment I have been giving the task of making my own rotating algorithm in python. This is my code so far.

import cv2
import math
import numpy as np

class rotator:

    angle = 20.0
    x = 330
    y = 330

    radians = float(angle*(math.pi/180))
    img = cv2.imread('FNAF.png',0)
    width,height = img.shape


    def showImg(name, self):
        cv2.imshow(name, self.img)
        self.img = np.pad(self.img, (self.height) ,'constant', constant_values=0)
        self.width,self.height = self.img.shape

    def printWH(self):
        print(self.width)
        print(self.height)

    def rotate(self):
        emptyF = np.zeros((self.width,self.height),dtype="uint8")
        emptyB = np.zeros((self.width,self.height),dtype="uint8")
        emptyBB = np.zeros((self.width,self.height),dtype="uint8")


        for i in range(self.width):
            for j in range(self.height):
                temp = self.img[i,j]
                #forward mapping
                xf = (i-self.x)*math.cos(self.radians)-(j-self.y)*math.sin(self.radians)+self.x
                yf = (i-self.x)*math.sin(self.radians)+(j-self.y)*math.cos(self.radians)+self.x
                #backward mapping should change the forward mapping to the original image
                xbb = (i-self.x)*math.cos(self.radians)+(j-self.y)*math.sin(self.radians)+self.x
                ybb = -(i-self.x)*math.sin(self.radians)+(j-self.y)*math.cos(self.radians)+self.x
                xbb = int(xbb)
                ybb = int(ybb)
                if xf < 660 and yf < 660 and xf>0 and yf > 0:
                    emptyF[int(xf),int(yf)] = temp
                else:
                    pass
                if xbb < 660 and ybb < 660 and xbb>0 and ybb > 0:
                    emptyBB[(xbb),(ybb)] = temp
                else:
                    pass
        cv2.imshow('Forward', emptyF)
        cv2.imshow('Backward', emptyBB)
def main():
    rotator.showImg('normal', rotator)
    rotator.printWH(rotator)
    rotator.rotate(rotator)
    cv2.waitKey(0)
    cv2.destroyAllWindows

if __name__ == '__main__':
    main()

Is there any way to improve this code or my algorithm? Any advise would be awesome.

NB. I also hav a problem with my backwards mapping. The output image has a lot of small black dots. Any suggestions to what that might be?

Please let me know.

Answer 1

The most common method for getting rid of the black dots is to paint over each pixel of the entire destination image with pixels copied from computed positions in the source image, instead of painting the source image pixels into computed positions in the destination image.

for i in range(660):
    for j in range(660):
        xb = int(...)
        yb = int(...)
        if xb in range(self.width) and yb in range(self.height):
            emptyF[i, j] = self.img[xb, yb]

Computing destination pixels positions from the source pixel positions may result in tiny areas unpainted in the destination due to numeric errors/limits.

Computing source pixels positions from the destination pixel position may result in a pixel value being copied to two adjacent locations, and other pixels never being copied from, but this is usually/often unnoticeable.