图像仿射变换之图像旋转实现

一. 实验代码

实验目标：实现输入图像绕中心点逆时针旋转30度

import cv2
import numpy as np

# affine transformation -> rotation
def affine(img, a, b, c, d, tx, ty):
    H, W, C = img.shape

    # temporary image
    tem = img.copy()
    img = np.zeros((H+2, W+2, C), dtype=np.float32)
    img[1:H+1, 1:W+1] = tem

    # get shape of new image
    H_new = np.round(H).astype(np.int)
    W_new = np.round(W).astype(np.int)
    out = np.zeros((H_new, W_new, C), dtype=np.float32)

    # get position of new image
    x_new = np.tile(np.arange(W_new), (H_new, 1))
    y_new = np.arange(H_new).repeat(W_new).reshape(H_new, -1)

    # get position of original image by affine
    adbc = a * d - b * c
    x = np.round((d * x_new  - b * y_new) / adbc).astype(np.int) - tx + 1
    y = np.round((-c * x_new + a * y_new) / adbc).astype(np.int) - ty + 1

    # adjust center by affine
    dcx = (x.max() + x.min()) // 2 - W//2
    dcy = (y.max() + y.min()) // 2 - H//2

    x -= dcx
    y -= dcy

    x = np.clip(x, 0, W + 1)
    y = np.clip(y, 0, H + 1)

    # assign pixcel
    out[y_new, x_new] = img[y, x]
    out = out.astype(np.uint8)

    return out

# Read image
img = cv2.imread("../paojie.jpg").astype(np.float32)

# Affine
A = 30.
theta = - np.pi * A / 180.

out = affine(img, a=np.cos(theta), b=-np.sin(theta), c=np.sin(theta), d=np.cos(theta),
 tx=0, ty=0)

# Save result
cv2.imshow("result", out)
cv2.imwrite("out.jpg", out)
cv2.waitKey(0)
cv2.destroyAllWindows()

---

二. 实验结果：

原图 ↑

 

逆时针旋转30度图像  ↑

 

---

三. 实验难点突破：

        https://www.cnblogs.com/wojianxin/p/12519498.html

        https://www.jianshu.com/p/1cfb3fac3798

---

四. 图像仿射变换简介：

        https://www.cnblogs.com/wojianxin/p/12518393.html