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Re: Re: Re: Optimization problem
Those functions seem to work great. I am analyzing high speed video
which luckily is easily parallizable but it still took quite a bit of
time to run using my old functions. Thanks for the help.
Adam
On Feb 22, 2009, at 3:12 AM, Matthias Odisio wrote:
> Adam,
>
>> Adam Simpson wrote:
>>> Hi, I'm currently working with some image files in mathematica but
>>> am
>>> having an optimization problem. What I am basically trying to do is
>>> convert an image to HSB color space and then test each pixel to
>>> see if
>>> the H,S,B values fall within a certain range, making it a 1 if
>>> it's in
>>> the specified range else a 0. Notice I have multiplied the raw HSV
>>> values to have ranges of [0,369], [0,100],[0,100] respectively. I
>>> however get an order of magnitude difference between running two
>>> operations that I can't rectify.
>>>
>>> Notice the image I am using to that I call "frame" is available for
>>> download at http://www.physics.uc.edu/~simpson/page11/files/OptimizationProblem.jpg
>>> :
>>>
>>> //test each pixel to see if the value of Hue,Saturation,Brightness
>>> fall within a certain range and make the value 1 if it is, else a 0:
>>> Image[Map[
>>> If[320 <= 359 #[[1]] <= 355 && 65 <= 100 #[[2]] <= 80 &&
>>> 30 <= 100 #[[3]] <= 75, 1, 0] &,
>>> ImageData[frame], {2}]] // AbsoluteTiming
>>>
>>> 0.282983 Seconds
>>>
>>> If however I create a function as such ,even after compiling it
>>> which
>>> helped slightly, that is equal to the above If statement I get an
>>> order of magnitude higher time.
>>>
>>> Hmin=320;
>>> Hmax=359;
>>> Smin=65;
>>> Smax=80;
>>> Bmin=30;
>>> Bmax=75;
>>>
>>> PixelMatch = Compile[{{H, _Real}, {S, _Real}, {B, _Real}},
>>> If[(Hmin <= H*359 <= Hmax) &&(Smin <= S*100 <= Smax) &&
>>> (Bmin <= B*100 <= Bmax), 1, 0]]
>>>
>>> Image[Map[PixelMatch[#[[1]], #[[2]], #[[3]]] &,
>>> ImageData[frame], {2}]] // AbsoluteTiming
>>>
>>> 2.012571 Seconds
>>>
>>> Any help is highly appreciated.
>>>
>>> Adam Simpson
>
> Map automatically tries to compile the function you specify.
>
> With your first approach, I would recommend using Binarize or
> ImageApply
> for the job, as they could get optimized in further versions:
>
> With[{hmin = 320/359., hmax = 355/359., smin = .65, smax = .8,
> bmin = .3, bmax = .75},
> Binarize[frame,
> hmin <= #[[1]] <= hmax && smin <= #[[2]] <= smax &&
> bmin <= #[[3]] <= bmax &]] // AbsoluteTiming
>
> 0.212292 s.
>
> A much faster approach is to process the whole 2d arrays at one go
> using
> functions which can operate on them directly:
>
> With[{hmin = 320/359., hmax = 355/359., smin = .65, smax = .8,
> bmin = .3, bmax = .75},
> Image[Unitize[
> Times @@
> MapThread[
> Clip[#1, #2, {0, 0}] &, {ImageData[frame,
> Interleaving -> False], {{hmin, hmax}, {smin, smax}, {bmin,
> bmax}}}]], "Bit"]] // AbsoluteTiming
>
> 0.088738 s.
>
>
> Matthias Odisio
> Wolfram Research
>
>
>
>
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