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woolpeeker/draw_matches.py

Last active April 21, 2025 19:07
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Python replacement for cv2.drawMatches(), for which there are no Python bindings in a release version.
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draw_matches.py
# drawMatches numpy version
def draw_matches(img1, kp1, img2, kp2, matches, color=None):
"""Draws lines between matching keypoints of two images.
Keypoints not in a matching pair are not drawn.
Places the images side by side in a new image and draws circles
around each keypoint, with line segments connecting matching pairs.
You can tweak the r, thickness, and figsize values as needed.
Args:
img1: An openCV image ndarray in a grayscale or color format.
kp1: ndarray [n1, 2]
img2: An openCV image ndarray of the same format and with the same
element type as img1.
kp2: ndarray [n2, 2]
matches: ndarray [n_match, 2]
img1 keypoints and whose queryIdx attribute refers to img2 keypoints.
color: The color of the circles and connecting lines drawn on the images.
A 3-tuple for color images, a scalar for grayscale images. If None, these
values are randomly generated.
"""
# We're drawing them side by side. Get dimensions accordingly.
# Handle both color and grayscale images.
if len(img1.shape) == 3:
new_shape = (max(img1.shape[0], img2.shape[0]), img1.shape[1]+img2.shape[1], img1.shape[2])
elif len(img1.shape) == 2:
new_shape = (max(img1.shape[0], img2.shape[0]), img1.shape[1]+img2.shape[1])
new_img = np.zeros(new_shape, type(img1.flat[0]))
# Place images onto the new image.
new_img[0:img1.shape[0],0:img1.shape[1]] = img1
new_img[0:img2.shape[0],img1.shape[1]:img1.shape[1]+img2.shape[1]] = img2
# Draw lines between matches. Make sure to offset kp coords in second image appropriately.
r = 15
thickness = 2
if color:
c = color
for m in matches:
# Generate random color for RGB/BGR and grayscale images as needed.
if not color:
c = np.random.randint(0,256,3) if len(img1.shape) == 3 else np.random.randint(0,256)
# So the keypoint locs are stored as a tuple of floats. cv2.line(), like most other things,
# wants locs as a tuple of ints.
end1 = tuple(np.round(kp1[m[0]]).astype(int))
end2 = tuple(np.round(kp2[m[1]]).astype(int) + np.array([img1.shape[1], 0]))
cv2.line(new_img, end1, end2, c, thickness)
cv2.circle(new_img, end1, r, c, thickness)
cv2.circle(new_img, end2, r, c, thickness)
return new_img
# drawMatches cv2 version
def draw_matches(img1, kp1, img2, kp2, matches, color=None):
"""Draws lines between matching keypoints of two images.
Keypoints not in a matching pair are not drawn.
Places the images side by side in a new image and draws circles
around each keypoint, with line segments connecting matching pairs.
You can tweak the r, thickness, and figsize values as needed.
Args:
img1: An openCV image ndarray in a grayscale or color format.
kp1: A list of cv2.KeyPoint objects for img1.
img2: An openCV image ndarray of the same format and with the same
element type as img1.
kp2: A list of cv2.KeyPoint objects for img2.
matches: A list of DMatch objects whose trainIdx attribute refers to
img1 keypoints and whose queryIdx attribute refers to img2 keypoints.
color: The color of the circles and connecting lines drawn on the images.
A 3-tuple for color images, a scalar for grayscale images. If None, these
values are randomly generated.
"""
# We're drawing them side by side. Get dimensions accordingly.
# Handle both color and grayscale images.
if len(img1.shape) == 3:
new_shape = (max(img1.shape[0], img2.shape[0]), img1.shape[1]+img2.shape[1], img1.shape[2])
elif len(img1.shape) == 2:
new_shape = (max(img1.shape[0], img2.shape[0]), img1.shape[1]+img2.shape[1])
new_img = np.zeros(new_shape, type(img1.flat[0]))
# Place images onto the new image.
new_img[0:img1.shape[0],0:img1.shape[1]] = img1
new_img[0:img2.shape[0],img1.shape[1]:img1.shape[1]+img2.shape[1]] = img2
# Draw lines between matches. Make sure to offset kp coords in second image appropriately.
r = 15
thickness = 2
if color:
c = color
for m in matches:
# Generate random color for RGB/BGR and grayscale images as needed.
if not color:
c = np.random.randint(0,256,3) if len(img1.shape) == 3 else np.random.randint(0,256)
# So the keypoint locs are stored as a tuple of floats. cv2.line(), like most other things,
# wants locs as a tuple of ints.
end1 = tuple(np.round(kp1[m.trainIdx].pt).astype(int))
end2 = tuple(np.round(kp2[m.queryIdx].pt).astype(int) + np.array([img1.shape[1], 0]))
cv2.line(new_img, end1, end2, c, thickness)
cv2.circle(new_img, end1, r, c, thickness)
cv2.circle(new_img, end2, r, c, thickness)
plt.figure(figsize=(15,15))
plt.imshow(new_img)
plt.show()
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woolpeeker commented Dec 22, 2023 via email

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