* Iterator mode: Mirror. Does the mode make a huge difference?
* I can not find any reference to PyArrayNeightborhoodIter_Next2d, where can I
find it?
* I think that making a copy on reset is (maybe in addition to the creation),
since there is a reset for every change of the parent iterator, and after this
change, the neighborhood can be determined.
* What do you think about the following idea?
* A neighbourhood iterator generator that accepts also a buffer to copy in
the neighbourhood.
* A reset function that would refill the buffer after each parent iterator
modification
Nadav
-----Original Message-----
From: numpy-discussion-boun...@scipy.org
[mailto:numpy-discussion-boun...@scipy.org] On Behalf Of David Cournapeau
Sent: Monday, October 24, 2011 9:38 AM
To: Discussion of Numerical Python
Subject: Re: [Numpy-discussion] neighborhood iterator speed
On Mon, Oct 24, 2011 at 6:57 AM, Nadav Horesh <nad...@visionsense.com> wrote:
> I am trying to replace an old code (biliteral filter) that rely on
> ndimage.generic_filter with the neighborhood iterator. In the old code, the
> generic_filter generates a contiguous copy of the neighborhood, thus the
> (cython) code could use C loop to iterate over the neighbourhood copy. In the
> new code version the PyArrayNeighborhoodIter_Next must be called to retrieve
> every neighbourhood item. The results of rough benchmarking to compare
> bilateral filtering on a 1000x1000 array:
> Old code (ndimage.generic_filter): 16.5 sec
> New code (neighborhood iteration): 60.5 sec
> New code with PyArrayNeighborhoodIter_Next omitted: 1.5 sec
>
> * The last benchmark is not "real" since the omitted call is a must. It just
> demonstrates the iterator overhead.
> * I assune the main overhead in the old code is the python function callback
> process. There are instructions in the manual how to wrap a C code for a
> faster callback, but I rather use the neighbourhood iterator as I consider it
> as more generic.
>
I am afraid the cost is unavoidable: you are really trading cpu for
memory. When using PyArrayNeighborhood_Next, there is a loop with a
condiational within, and I don't think those can easily be avoided
without losing genericity. Which mode are you using when creating the
neighborhood iterator ?
There used to be a PyArrayNeightborhoodIter_Next2d, I don't know why I
commented out. You could try to see if you can get faster.
> If the PyArrayNeighborhoodIter_Reset could (optionally) copy the relevant
> data (as the generic_filter does) it would provide a major speed up in many
> cases.
Optionally copying may be an option, but it would make more sense to
do it at creation time than during reset, no ? Something like a binary
and with the current mode flag,
cheers,
David
_______________________________________________
NumPy-Discussion mailing list
NumPy-Discussion@scipy.org
http://mail.scipy.org/mailman/listinfo/numpy-discussion
__________ Information from ESET NOD32 Antivirus, version of virus signature
database 4628 (20091122) __________
The message was checked by ESET NOD32 Antivirus.
http://www.eset.com
_______________________________________________
NumPy-Discussion mailing list
NumPy-Discussion@scipy.org
http://mail.scipy.org/mailman/listinfo/numpy-discussion
