extracting patch of a certain size at certain angle with given center from an image using python

Question

For my project I want to extract a patch of size 224x224 from an image of size 1024x720 at a specific angle using python. The pixel location for the patch center on the image is given and the angle made by patch is also given. I know how to extract patch at 0(degree) angle using array slicing, but i want to slice the image at an angle. Any help regarding the same will be appreciated. thanks!

Answer 1

from scipy import ndimage
import numpy as np
import math as m
import cv2   
 def patchmaker(img,height,width,center_y,center_x,angle):
        theta = angle/180*3.14
        img_shape = np.shape(img)
        print(img_shape)
        x = [[i for i in range(0,img_shape[1])] for y in range(img_shape[0])]
        y = [[j for i in range(img_shape[1])] for j in range(0,img_shape[0])]
        x = np.asarray(x)
        y = np.asarray(y)
        rotatex = x[center_y-m.floor(height/2):center_y+m.floor(height/2),center_x-m.floor(width/2):center_x+m.floor(width/2)]
        rotatey = y[center_y-m.floor(height/2):center_y+m.floor(height/2),center_x-m.floor(width/2):center_x+m.floor(width/2)]
        coords   = [rotatex.reshape((1,height*width))-center_x,rotatey.reshape((1,height*width))-center_y]
        coords = np.asarray(coords)
        coords = coords.reshape(2,height*width)
        roatemat = [[m.cos(theta),m.sin(theta)],[-m.sin(theta),m.cos(theta)]]
        rotatedcoords = np.matmul(roatemat,coords)
        patch = ndimage.map_coordinates(img,[rotatedcoords[1]+center_y,rotatedcoords[0]+center_x], order=1, mode='nearest').reshape(height,width)
        return patch