kornia_moons

Conversions between kornia and other computer vision libraries formats, mainly OpenCV.

What's inside

• Keypoint / LAF conversions — OpenCV cv2.KeyPoint ↔ kornia local affine frames (LAFs), handling the differing scale and orientation conventions (mrSize=6.0 for SIFT, 1.0 for ORB): laf_from_opencv_SIFT_kpts, opencv_ORB_kpts_from_laf, …
• Match conversions — kornia match tensors ↔ cv2.DMatch lists: cv2_matches_from_kornia, kornia_matches_from_cv2
• OpenCV detectors as kornia modules — OpenCVDetectorKornia, OpenCVFeatureKornia, OpenCVDetectorWithAffNetKornia (with kornia AffNet shape refinement)
• Visualization — LAFs (visualize_LAF), matches with inliers/epipolar lines/reprojected corners (draw_LAF_matches), plain point matches from LoFTR-style matchers (draw_point_matches), epipolar errors, and SOLD2 line segments (plot_lines, plot_color_line_matches)

Install

pip install kornia_moons

Quick start: keypoint conversion

import matplotlib.pyplot as plt
import cv2
from kornia.image import image_to_tensor

from kornia_moons.feature import laf_from_opencv_ORB_kpts, opencv_ORB_kpts_from_laf
from kornia_moons.viz import visualize_LAF

img = cv2.cvtColor(cv2.imread('data/strahov.png'), cv2.COLOR_BGR2RGB)

det = cv2.ORB_create(500)
kps, descs = det.detectAndCompute(img, None)

out_img = cv2.drawKeypoints(img, kps, None, flags=cv2.DRAW_MATCHES_FLAGS_DRAW_RICH_KEYPOINTS)
plt.imshow(out_img)

lafs = laf_from_opencv_ORB_kpts(kps)
visualize_LAF(image_to_tensor(img, False), lafs, 0)

kps_back = opencv_ORB_kpts_from_laf(lafs)
out_img2 = cv2.drawKeypoints(img, kps_back, None, flags=cv2.DRAW_MATCHES_FLAGS_DRAW_RICH_KEYPOINTS)
plt.imshow(out_img2)

Matching and visualization

import cv2
import numpy as np
import torch
import kornia

from kornia_moons.feature import laf_from_opencv_SIFT_kpts
from kornia_moons.viz import draw_LAF_matches

det = cv2.SIFT_create(100)
img1 = cv2.cvtColor(cv2.imread('data/strahov.png'), cv2.COLOR_BGR2RGB)

Hgt = np.array([[0.5, 0.1, 10], [-0.1, 0.5, 10], [0, 0, 1]])
img2 = cv2.warpPerspective(img1, Hgt, img1.shape[:2][::-1], borderValue=(255, 255, 255))

kps1, descs1 = det.detectAndCompute(img1, None)
lafs1 = laf_from_opencv_SIFT_kpts(kps1)
kps2, descs2 = det.detectAndCompute(img2, None)
lafs2 = laf_from_opencv_SIFT_kpts(kps2)

match_dists, match_idxs = kornia.feature.match_snn(
    torch.from_numpy(descs1).float(), torch.from_numpy(descs2).float(), 0.98)

H, mask = cv2.findHomography(
    kornia.feature.get_laf_center(lafs1[:, match_idxs[:, 0]]).numpy().reshape(-1, 2),
    kornia.feature.get_laf_center(lafs2[:, match_idxs[:, 1]]).numpy().reshape(-1, 2),
    cv2.USAC_MAGSAC, 0.5)

draw_LAF_matches(lafs1, lafs2, match_idxs, img1, img2, mask,
                 draw_dict={"inlier_color": (0.2, 1, 0.2),
                            "tentative_color": (0.8, 0.8, 0),
                            "feature_color": None,
                            "vertical": False}, H=H)

Learn more

• Local features tutorial — conversions in both directions, matches, detector wrappers
• Visualization tutorial — matches, epipolar geometry, SOLD2 line segments
• API reference

Development

pip install -e ".[dev]"
pytest tests                                # unit tests
pytest --nbmake docs/feature.ipynb docs/viz.ipynb   # run the docs notebooks
mkdocs serve                                # preview docs locally