I have used convolution2d to generate some statistics on conditions of local patterns. To be complete, I'm working with images and the value 0.5 is my 'gray-screen', I cannot use masks before this unfortunately (dependence on some other packages). I want to add new objects to my image, but it should overlap at least 75% of non-gray-screen. Let's assume the new object is square, I mask the image on gray-screen versus the rest, do a 2-d convolution with a n by n matrix filled with 1s so I can get the sum of the number of gray-scale pixels in that patch. This all works, so I have a matrix with suitable places to place my new object. How do I efficiently pick a random one from this matrix?
Here is a small example with a 5x5 image and a 2x2 convolution matrix, where I want a random coordinate in my last matrix with a 1 (because there is at most 1 0.5 in that patch)
Image:
1 0.5 0.5 0 1
0.5 0.5 0 1 1
0.5 0.5 1 1 0.5
0.5 1 0 0 1
1 1 0 0 1
Convolution matrix:
1 1
1 1
Convoluted image:
3 3 1 0
4 2 0 1
3 1 0 1
1 0 0 0
Conditioned on <= 1:
0 0 1 1
0 0 1 1
0 1 1 1
1 1 1 1
How do I get a uniformly distributed coordinate of the 1s efficiently?
np.where
and np.random.randint
should do the trick :
#we grab the indexes of the ones
x,y = np.where(convoluted_image <=1)
#we chose one index randomly
i = np.random.randint(len(x))
random_pos = [x[i],y[i]]
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