chapter-11-part-1.py

import argparse
import cv2
import numpy as np
#What is epipolar geometry?
def build_arg_parser():
    parser = argparse.ArgumentParser(description='Find fundamental matrix \
    using the two input stereo images and draw epipolar lines')
    parser.add_argument("--img-left", dest="img_left", required=True,
    help="Image captured from the left view")
    parser.add_argument("--img-right", dest="img_right", required=True,
    help="Image captured from the right view")
    parser.add_argument("--feature-type", dest="feature_type",
    required=True, help="Feature extractor that will be used; can \
    be either 'sift' or 'surf'")
    return parser

def draw_lines(img_left, img_right, lines, pts_left, pts_right):
    h,w = img_left.shape
    img_left = cv2.cvtColor(img_left, cv2.COLOR_GRAY2BGR)
    img_right = cv2.cvtColor(img_right, cv2.COLOR_GRAY2BGR)
    for line, pt_left, pt_right in zip(lines, pts_left, pts_right):
        x_start,y_start = map(int, [0, -line[2]/line[1] ])
        x_end,y_end = map(int, [w, -(line[2]+line[0]*w)/line[1] ])
        color = tuple(np.random.randint(0,255,2).tolist())
        cv2.line(img_left, (x_start,y_start), (x_end,y_end), color,1)
        cv2.circle(img_left, tuple(pt_left), 5, color, -1)
        cv2.circle(img_right, tuple(pt_right), 5, color, -1)
    return img_left, img_right

def get_descriptors(gray_image, feature_type):
    if feature_type == 'surf':
        feature_extractor = cv2.SURF()
    elif feature_type == 'sift':
        feature_extractor = cv2.SIFT()
    else:
        raise TypeError("Invalid feature type; should be either 'surf' or \
    'sift'")
    keypoints, descriptors = feature_extractor.detectAndCompute(gray_image,None)
    return keypoints, descriptors

if __name__=='__main__':
    args = build_arg_parser().parse_args()
    img_left = cv2.imread(args.img_left,0) # left image
    img_right = cv2.imread(args.img_right,0) # right image
    feature_type = args.feature_type
    if feature_type not in ['sift', 'surf']:
        raise TypeError("Invalid feature type; has to be either 'sift' or \
    'surf'")
    scaling_factor = 1.0
    img_left = cv2.resize(img_left, None, fx=scaling_factor,fy=scaling_factor, interpolation=cv2.INTER_AREA)
    img_right = cv2.resize(img_right, None, fx=scaling_factor,fy=scaling_factor, interpolation=cv2.INTER_AREA)
    kps_left, des_left = get_descriptors(img_left, feature_type)
    kps_right, des_right = get_descriptors(img_right, feature_type)
    # FLANN parameters
    FLANN_INDEX_KDTREE = 0
    index_params = dict(algorithm = FLANN_INDEX_KDTREE, trees = 5)
    search_params = dict(checks=50)
    # Get the matches based on the descriptors
    flann = cv2.FlannBasedMatcher(index_params, search_params)
    matches = flann.knnMatch(des_left, des_right, k=2)
    pts_left_image = []
    pts_right_image = []
    # ratio test to retain only the good matches
    for i,(m,n) in enumerate(matches):
        if m.distance < 0.7*n.distance:
            pts_left_image.append(kps_left[m.queryIdx].pt)
            pts_right_image.append(kps_right[m.trainIdx].pt)
    pts_left_image = np.float32(pts_left_image)
    pts_right_image = np.float32(pts_right_image)
    F, mask = cv2.findFundamentalMat(pts_left_image, pts_right_image,cv2.FM_LMEDS)
    # Selecting only the inliers
    pts_left_image = pts_left_image[mask.ravel()==1]
    pts_right_image = pts_right_image[mask.ravel()==1]
    # Drawing the lines on left image and the corresponding feature points on the right image
    lines1 = cv2.computeCorrespondEpilines(pts_right_image.reshape(-1,1,2), 2, F)
    lines1 = lines1.reshape(-1,3)
    img_left_lines, img_right_pts = draw_lines(img_left, img_right, lines1,pts_left_image, pts_right_image)
    # Drawing the lines on right image and the corresponding feature points on the left image
    lines2 = cv2.computeCorrespondEpilines (pts_left_image.reshape(-1,1,2),1,F)
    lines2 = lines2.reshape(-1,3)
    img_right_lines, img_left_pts = draw_lines(img_right, img_left, lines2,pts_right_image, pts_left_image)
    cv2.imshow('Epi lines on left image', img_left_lines)
    cv2.imshow('Feature points on right image', img_right_pts)
    cv2.imshow('Epi lines on right image', img_right_lines)
    cv2.imshow('Feature points on left image', img_left_pts)
    cv2.waitKey()
    cv2.destroyAllWindows()