Optimize NumPy iterating through image and changing values

Question

Is there a way to optimize this snippet of code? With my current im value, it is taking me ~28 seconds. Wondering if I could reduce this time.

im = output_image[-min_xy[1]:-min_xy[1] + image_2.shape[0], -min_xy[0]:-min_xy[0] + image_2.shape[1]]
    for idx, rk in enumerate(im):
        for ix, k in enumerate(rk):
            image_2[idx][ix] = avg(im[idx][ix], image_2[idx][ix])

type(image_2) and type(im) is <type 'numpy.ndarray'>

im.shape and image_2.shape is (2386, 3200, 3)

what my avg() does is

def avg(a1, a2):
    if [0., 0., 0.] in a1:
        return a2
    else:
        return (a1 + a2) / 2

NOTE: a1 is an array of size 3 ex: array([ 0.68627451, 0.5372549 , 0.4745098])

Try to see if your algorithm behaves like any matrix transformations or operations? — Austin A
– Austin A, Commented Oct 18, 2017 at 22:29
With if [0., 0., 0.] in a1 its checking if anyone in a1 is zero. Are you sure you want that? — Divakar
– Divakar, Commented Oct 18, 2017 at 22:45
@Liondancer That doesn't answer my question, which was - With if [0., 0., 0.] in a1:, are you trying to check if ALL elements in a1 are zeros OR if ANY one element in a1 is zero? — Divakar
– Divakar, Commented Oct 19, 2017 at 4:16

Divakar · Accepted Answer · 2017-10-18 22:58:39Z

1

The only obstacle to vectorization seemed to be that IF conditional in avg. To get past it, simply use the choosing capability of np.where and thus have our solution like so -

avgs = (im + image_2)/2.0
image_2_out = np.where((im == 0).any(-1,keepdims=1), image_2, avgs)

Note that this assumes with if [0., 0., 0.] in a1, you meant to check for ANY one match. If you meant to check for ALL zeros, simply use .all instead of .any.

Alternatively, to do in-situ edits in image_2, use a mask for boolean-indexing -

mask = ~(im == 0).any(-1)
image_2[mask] = avgs[mask]

edited Oct 18, 2017 at 22:58

answered Oct 18, 2017 at 22:51

Divakar

222k19 gold badges273 silver badges374 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Optimize NumPy iterating through image and changing values

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related