Roadmap to 0.4

[Stéfan van der Walt]

Hi Andy,

Sorry for the late reply.

On Tue, Oct 25, 2011 at 12:17 AM, Andreas Mueller
<amueller at ais.uni-bonn.de> wrote:
>>> - Support for multiple computation back-ends
>>
>> Would anyone like to comment on this issue?
>
> Could you give an example on how you picture this?
> I think I get the general idea but I'm not sure how you would implement it.
> You want the user to provide some other computational backend that
> is somehow plugged into scikits-image, as far as i understand.
>
> Also: Do you think the easy switching between the implementations
> is a good enough reason for the additional complexity?

I've learnt that we cannot satisfy all the people all of the time.
Some people want interesting algorithms, other people want very fast
execution times.  Since we can't write code for all those use cases at
the same time, I think our best option is to help them achieve their
goal with minimum effort.

So, all that this framework allows you to do is basically "outsource"
skimage functions.  For example, you can say:

"Instead of calling sobel from skimage, use this sobel implementation
I found in opencv"

Usually, this will require you to write code that can only be run on
an opencv system, but with the plugin system you can easily share that
code with colleagues who do not have opencv installed:

use_backend('my_opencv_routines')
output = sobel(input)

If the opencv backend is not found, the backend gracefully falls back
to the NumPy / Cython implementation.

Yes, the complexity opens some doors for weird things to happen.  For
example, if implementations (say, e.g., opencv vs.
CUDA vs NumPy) return subtly different results, your script won't give
the same result on all machines.  To compensate, we've added utility
functions to the test suite, so that you can do:

@add_backends
def mytest():
    for b in backends:
        output = sobel(input, backend=b)
        [...check_output...]

> Don't get me wrong, I'm not as opposed as it might sound, I'm just
> trying to figure the idea out ;)

All critical feedback is most welcome (and necessary)!  Let's keep the
discussion going.

Cheers
Stéfan