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Re: Re: Optimization problem
Thanks, but upon running the two functions you supplied I got pretty
much the same times as the slower original function. ~2 seconds
compared to ~.2 seconds when the If statement is directly inside of
Map[].
On Feb 21, 2009, at 7:40 PM, Daniel Lichtblau wrote:
> 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
>
> It's a scoping issue, more or less, having to do with Compile having
> HoldAll attribute. If you check your PixelMatch[[4]] you will see it
> is
> actually making several function calls.
>
> This can be rectified using either approach below. The first forces an
> evaluation of teh body of the Compile. The second makes the values
> visible to everything inside the With[], including the body of that
> Compile.
>
> PixelMatch2 = Compile[{{H, _Real}, {S, _Real}, {B, _Real}},
> Evaluate[If[(Hmin <= H*359 <= Hmax) &&(Smin <= S*100 <= Smax) &&
> (Bmin <= B*100 <= Bmax), 1, 0]]]
>
> PixelMatch3 = With[
> {Hmin=320, Hmax=359, Smin=65, Smax=80, Bmin=30, Bmax=75},
> Compile[{{H, _Real}, {S, _Real}, {B, _Real}},
> If[(Hmin <= H*359 <= Hmax) &&(Smin <= S*100 <= Smax) &&
> (Bmin <= B*100 <= Bmax), 1, 0]]]
>
> Daniel Lichtblau
> Wolfram Research
>
>
>
>
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