[Numpy-discussion] Error in nd_image filters?

Russel Howe russel at appliedminds.net
Tue Jun 7 08:10:30 CDT 2005


Good catch, I missed that one.  Thanks!
Russel
On Jun 3, 2005, at 3:04 PM, Peter Verveer wrote:

> That seems to be indeed correct. In fact the line 'weights[lw] =  
> -1.0' must also be changed to 'weights[lw] *= -1.0 / sd'. I  
> committed these changes to CVS.
>
> Thanks for spotting this, Peter
>
> On Jun 3, 2005, at 8:39 PM, Russel Howe wrote:
>
>
>> I think there is an error in the 2nd and 3rd derivative gaussian  
>> kernels in the nd_image module.  I have attached a patch which I  
>> believe has the correct formula, would someone please double-check  
>> me on this?
>> Thanks
>> Russel Howe
>> --- numarray-1.3.2/Packages/nd_image/Lib/filters.py 2005-03-08  
>> 15:58:08.000000000 -0800
>> +++ numarray-1.3.2-modified/Packages/nd_image/Lib/filters.py     
>> 2005-05-05 15:52:00.000000000 -0700
>> @@ -189,7 +189,7 @@
>>          weights[lw] = -1.0
>>          for ii in range(1, lw + 1):
>>              x = float(ii)
>> -            tmp = (2.0 * x * x / sd - 1.0) * weights[lw + ii]
>> +            tmp = ( x * x / sd - 1.0 ) * weights[lw + ii] / sd
>>              weights[lw + ii] = tmp
>>              weights[lw - ii] = tmp
>>      elif order == 3: # third derivative
>> @@ -197,7 +197,7 @@
>>          sd2 = sd * sd
>>          for ii in range(1, lw + 1):
>>              x = float(ii)
>> -            tmp = (6.0 - 4.0 * x * x / sd) * x * weights[lw + ii]
>> +            tmp = (3.0 - x * x / sd) * x * weights[lw + ii] /  
>> sd / sd
>>              weights[lw + ii] = tmp
>>              weights[lw - ii] = -tmp
>>      return correlate1d(input, weights, axis, origin = 0, mode =  
>> mode,
>>
>>
>>
>>
>>
>>
>>
>> -------------------------------------------------------
>> This SF.Net email is sponsored by: NEC IT Guy Games.  How far can  
>> you shotput
>> a projector? How fast can you ride your desk chair down the office  
>> luge track?
>> If you want to score the big prize, get to know the little guy.  
>> Play to win an NEC 61" plasma display: http://www.necitguy.com/?r=20
>> _______________________________________________
>> Numpy-discussion mailing list
>> Numpy-discussion at lists.sourceforge.net
>> https://lists.sourceforge.net/lists/listinfo/numpy-discussion
>>
>
>
>
> -------------------------------------------------------
> This SF.Net email is sponsored by: NEC IT Guy Games.  How far can  
> you shotput
> a projector? How fast can you ride your desk chair down the office  
> luge track?
> If you want to score the big prize, get to know the little guy.   
> Play to win an NEC 61" plasma display: http://www.necitguy.com/?r=20
> _______________________________________________
> Numpy-discussion mailing list
> Numpy-discussion at lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/numpy-discussion
>





More information about the Numpy-discussion mailing list