Keypoint detection: drawMatches on multiple images / confusion over DRAW_OVER_OUTIMG flag

Python
1

I’m using opencv-python, and I am trying to visualize results from AKAZE keypoint matching for multiple images. While playing around with drawMatches, several questions arose. Below is the code, and my questions:

import cv2

template_image cv2.imread("img1.tif")
target_image cv2.imread("img2.tif")

akaze = cv2.AKAZE_create()
kp1, des1 = akaze.detectAndCompute(template_image, None)
kp2, des2 = akaze.detectAndCompute(target_image, None)
matcher = cv2.DescriptorMatcher_create(cv2.DescriptorMatcher_BRUTEFORCE_HAMMING)
matches = matcher.knnMatch(des1, des2, 2)

good = []
for m, n in matches:
    if m.distance < 0.8 * n.distance:
        good.append(m)

results = cv2.drawMatches(template_image,kp1,
                          target_image,kp2,
                          good,None,
                          (0,255,0),
                          flags=1)

  1. What is the correct use of the DRAW_OVER_OUTIMG flag (flag “1”)? I tried the following, but I get an error:
    results = cv2.drawMatches(template_image, kp1, target_image, kp2, good, target_image, flags=1)

    error: OpenCV(3.4.9) C:\projects\opencv-python\opencv\modules\features2d\src\draw.cpp:156: error: (-201:Incorrect size of input array) outImg has size less than need to draw img1 and img2 together in function 'cv::_prepareImgAndDrawKeypoints'

  1. drawMatches takes takes only two images, but I would like to visualize keypoint matches between the template and multiple target images - is there any way to do this?

  2. Can I change the image-matrix layout in drawMatches?