Is OpenCV running two instances of SIFT detectAndCompute concurrently? - python-3.x

Question

I can get SIFT keypoints and descriptors from two, seperate, large images (~2GB) when I run sift.detectAndCompute from the command line. I run it on one image, wait a very long time, but eventually get the keypoints and descriptors. Then I repeat for the second image, and again it takes a long time, but I DO eventually get my keypoints and descriptors. Here are the two lines I run from the IPython console in Spyder, which I am running on my machine with 32 GB of RAM. (MAX_MATCHES = 50000 in the code below):
sift = cv2.xfeatures2d.SIFT_create(MAX_MATCHES)
keypoints, descriptors = sift.detectAndCompute(imgGray, None)
This takes 10 minutes to finish, but it does finish. Next, I run this:
keypoints2, descriptors2 = sift.detectAndCompute(refimgGray, None)
When done, keypoints and keypoints2 DO contain 50000 keypoint objects.
However, if I run my script, which calls a function that uses sift.detectAndCompute and returns keypoints and descriptors, the process takes a long time, uses 100% of my memory and ~95% of my disk BW and then fails with this traceback:
runfile('C:/AV GIS/python scripts/img_align_w_geo_w_mask_refactor_ret_1.py', wdir='C:/AV GIS/python scripts')
Reading reference image : C:\Users\kellett\Downloads\3074_transparent_mosaic_group1.tif
xfrm for image = (584505.1165100001, 0.027370000000000002, 0.0, 4559649.608440001, 0.0, -0.027370000000000002)
Reading image to align : C:\Users\kellett\Downloads\3071_transparent_mosaic_group1.tif
xfrm for image = (584499.92168, 0.02791, 0.0, 4559648.80372, 0.0, -0.02791)
Traceback (most recent call last):
File "<ipython-input-75-571660ddab7f>", line 1, in <module>
runfile('C:/AV GIS/python scripts/img_align_w_geo_w_mask_refactor_ret_1.py', wdir='C:/AV GIS/python scripts')
File "C:\Users\kellett\AppData\Local\Continuum\anaconda3\envs\testgdal\lib\site-packages\spyder_kernels\customize\spydercustomize.py", line 668, in runfile
execfile(filename, namespace)
File "C:\Users\kellett\AppData\Local\Continuum\anaconda3\envs\testgdal\lib\site-packages\spyder_kernels\customize\spydercustomize.py", line 108, in execfile
exec(compile(f.read(), filename, 'exec'), namespace)
File "C:/AV GIS/python scripts/img_align_w_geo_w_mask_refactor_ret_1.py", line 445, in <module>
matches = find_matches(refKP, refDesc, imgKP, imgDesc)
File "C:/AV GIS/python scripts/img_align_w_geo_w_mask_refactor_ret_1.py", line 301, in find_matches
matches = matcher.match(dsc1, dsc2)
error: C:\ci\opencv_1512688052760\work\modules\core\src\stat.cpp:4024: error: (-215) (type == 0 && dtype == 4) || dtype == 5 in function cv::batchDistance
The function is simply called once for each image thusly:
print("Reading image to align : ", imFilename);
img, imgGray, imgEdgmask, imgXfrm, imgGeoInfo = read_ortho4align(imFilename)
refKP, refDesc = extractKeypoints(refimgGray, refEdgmask)
imgKP, imgDesc = extractKeypoints(imgGray, imgEdgmask)
HERE IS MY QUESTION (sorry for shouting): Do you think Python tries to run the two lines above concurrently in some way? If so, how can I force it to run serially? If not, do you have any idea why the two keypoint detections would work individually, but not when they come one after another in a script?
One more clue - I put in a statement to see if the script proceeds to the second detectAndCompute statement before it fails, and it does. (I just put a print statement in between the two.)

Answer 1

My error was coming later in my script where I was finding matches.
I have no reason to believe the two SIFT keypoint finding processes are occurring at the same time.
I downsampled the images I was searching for SIFT keypoints and was able to iterate my troubleshooting more quickly and found my error.
I will look at my error more closely next time before asking a question.