[Chimera-users] Laplacian filter on density maps

[Grigore Pintilie]

Hi Tom,

Thank you very much for this implementation, I will experiment with
it. You're absolutely right that the Laplacian is very sensitive to
noise, point well made!

Greg


On Fri, Nov 21, 2008 at 6:28 PM, Tom Goddard <goddard at cgl.ucsf.edu> wrote:
> Hi Greg,
>
>  I've added volume Laplacian calculation to Chimera.  It is available via
> the volume operation "vop" command.  To calculate the Laplacian of model #3
> use
>
>   vop #3 laplacian
>
> It will create a new volume data set.  This will be in tonight's Chimera 1.4
> daily builds.
>
>   http://www.cgl.ucsf.edu/chimera/alpha-downloads.html
>
>  Tom
>
>
>
> Tom Goddard wrote:
>>
>> Hi Greg,
>>
>>  A Laplacian filter is simple to implement.  I'll see if I can add it to
>> the "vop" command later this week.  The Laplacian filter roughly speaking
>> does edge detection so alignments of filtered maps will try to match the
>> boundaries of the objects.  The Laplacian is a sum of second derivatives and
>> will be useless on noisy data (e.g. any tomography) unless you smooth the
>> data first with for instance a Gaussian filter.
>>
>>    Tom
>>
>>
>> Grigore Pintilie wrote:
>>
>>>
>>> Hi,
>>>
>>> Just wondering if it might be possible to apply a Laplacian filter on
>>> a density map in chimera. The reason I'm asking is that if the
>>> cross-correlation is computed with laplacian-filtered maps it gives
>>> more robust results for the correct alignments vs. non-correct
>>> alignments.
>>>
>>> Thanks,
>>>
>>> Greg
>>>
>
>