[Numpy-discussion] Speed performance on array constant set
Travis Oliphant
oliphant.travis at ieee.org
Fri Jan 20 08:42:02 CST 2006
Mark Heslep wrote:
> Im doing some work with the OpenCv* project. Im using swig typemaps
> to convert the Cv data structures to numarray which works well. Id
> like to restrict Cv use to what its strengths: complicated vision
> processing algorithms like optical flow. For the case of simple Cv
> data manipulations, I'd rather use NumPy functions & methods but was
> surprised at the performance comparison.
> - A simple scalar constant fill with cvSet. 'im' here is a wrapped Cv
> image data structure.
>
>> python -m timeit -s "import opencv.cv as cv; im =
>> cv.cvCreateImage(cv.cvSize(1000,1000), 8, 1)" "cv.cvSet( im,
>> cv.cvRealScalar( 7 ) )"
>> 100 loops, best of 3: 2.58 msec per loop
>
>
> - If I try the equivalent with NumPy
>
>> python -m timeit -s "import numarray as na; a = na.zeros((1000,1000)
>> )" "a[:,:] = 7"
>
>
>> 10 loops, best of 3: 45.1 msec per loop
>
>
> A >10x hit. Am I using the preferred / optimal NumPy method here? I
> scanned the earlier Scalar posts but thought that was boolean type
> only issue.
>
First of all, try using NumPy instead of Numarray: import numpy as na
Second: use math (i.e. a += 7)
Third: There are specialized fill routines .fill() in numpy and a
simliar routine in Numarray that can be faster then indexing.
Best,
-Travis
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