transform.py

import cv2
import numpy as np

def get_affine_transform(center,
                         scale,
                         rot,
                         output_size,
                         shift=np.array([0, 0], dtype=np.float32),
                         inv=0,):
    if not isinstance(scale, np.ndarray) and not isinstance(scale, list):
        print(scale)
        scale = np.array([scale, scale])

    src_w = scale[0]
    dst_w = output_size[0]
    dst_h = output_size[1]

    rot_rad = np.pi * rot / 180
    src_dir = get_dir([0, src_w * -0.5], rot_rad)
    dst_dir = np.array([0, dst_w * -0.5], np.float32)

    src = np.zeros((3, 2), dtype=np.float32)
    dst = np.zeros((3, 2), dtype=np.float32)
    src[0, :] = center + scale * shift
    src[1, :] = center + src_dir + scale * shift
    dst[0, :] = [dst_w * 0.5, dst_h * 0.5]
    dst[1, :] = np.array([dst_w * 0.5, dst_h * 0.5]) + dst_dir

    src[2:, :] = get_3rd_point(src[0, :], src[1, :])
    dst[2:, :] = get_3rd_point(dst[0, :], dst[1, :])

    if inv:
        trans = cv2.getAffineTransform(np.float32(dst), np.float32(src))
    else:
        trans = cv2.getAffineTransform(np.float32(src), np.float32(dst))

    return trans


# 실제 어파인 변환 수행하는 부분
# t는 위의 get_affine_transform 함수를 통해 trans 매트릭스 구한다.
def affine_transform(pt, t):
    new_pt = np.array([pt[0], pt[1], 1.]).T
    new_pt = np.dot(t, new_pt)
    return new_pt[:2]

def get_dir(src_point, rot_rad):
    """ 
        Transformation Matrix 
        x = x * cosΘ - y * sinΘ
        y = x * cosΘ + y * sinΘ
        [ cosΘ   sinΘ   0]
        [ -sinΘ  cosΘ   0]
        [  0       0    0]
    """

    sn, cs = np.sin(rot_rad), np.cos(rot_rad)

    src_result = [0, 0]
    src_result[0] = src_point[0] * cs - src_point[1] * sn
    src_result[1] = src_point[0] * sn + src_point[1] * cs

    return src_result


def get_3rd_point(a, b):
    direct = a - b
    return b + np.array([-direct[1], direct[0]], dtype=np.float32)