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Re: inverse gradient [message #64061 is a reply to message #63980]

Fri, 28 November 2008 08:14

pgrigis
Messages: 436
Registered: September 2007

Senior Member

If the original poster has a gradient image A and wants to compute
the image B whose gradient is A, then it seems odd to me that a
sparse approach would work.

Ciao,
Paolo

Jeremy Bailin wrote:
> On Nov 28, 4:31�am, erano <eran.o...@gmail.com> wrote:
>> On Nov 27, 5:24�pm, Jeremy Bailin <astroco...@gmail.com> wrote:
>>
>>
>>
>>> On Nov 27, 3:27�am, erano <eran.o...@gmail.com> wrote:
>>
>>>> > "inverse" meaning what for a vector-field?
>>
>>>> > Paolo
>>
>>>> "inverse" is the opposite operation for gradient.
>>>> The inputs are 2D gradient images (dX and dY), where high values are
>>>> large changes in the "inverse gradient" image, and zeros are stable
>>>> (no changes) in the "inverse gradient".
>>
>>>> Eran
>>
>>> I would never use this in production code, but here's a hack that will
>>> give you something to look at:
>>
>>> scalarfield = total(dX, /cumulative, 1) + total(dY, /cumulative, 2)
>>
>>> The real solution is to replace those totals with actual integrals.
>>
>>> -Jeremy.
>>
>> Thanks,
>>
>> It's the simplest way. it's basicly works but with errors.
>> I found few articlies about "inverse gradient" on the web, and the
>> problem is very complex and the simple MATLAB function (from matlab
>> exchange) is expensive (memory).
>> The main problem is to solve A*F=V where A is M*N matrix, V is vector
>> and we look for F.
>> I used �LA_LEAST_SQUARES (with all possible methods) for solve this
>> but it is slow and have memory problem. please note that most of A
>> matrix are zeros...
>>
>> Any ideas?
>
> Oddly enough, that's the second time sparse arrays have come up in one
> week!
>
> You want LINBCG, which takes as input a sparse matrix created using
> SPRSIN. The help pages on them are pretty decent - give them a read.
>
> -Jeremy.

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[Message index]

		inverse gradient By: erano on Wed, 26 November 2008 02:10
		Re: inverse gradient By: pgrigis on Tue, 02 December 2008 10:59
		Re: inverse gradient By: erano on Tue, 02 December 2008 11:42
		Re: inverse gradient By: erano on Tue, 02 December 2008 10:50
		Re: inverse gradient By: pgrigis on Tue, 02 December 2008 09:20
		Re: inverse gradient By: erano on Tue, 02 December 2008 09:04
		Re: inverse gradient By: pgrigis on Tue, 02 December 2008 07:45
		Re: inverse gradient By: erano on Tue, 02 December 2008 07:12
		Re: inverse gradient By: pgrigis on Tue, 02 December 2008 06:45
		Re: inverse gradient By: erano on Tue, 02 December 2008 01:27
		Re: inverse gradient By: pgrigis on Fri, 28 November 2008 08:31
		Re: inverse gradient By: pgrigis on Fri, 28 November 2008 08:18
		Re: inverse gradient By: pgrigis on Fri, 28 November 2008 08:14
		Re: inverse gradient By: pgrigis on Fri, 28 November 2008 08:10
		Re: inverse gradient By: Jeremy Bailin on Fri, 28 November 2008 05:27
		Re: inverse gradient By: erano on Fri, 28 November 2008 01:31
		Re: inverse gradient By: Jeremy Bailin on Thu, 27 November 2008 06:24
		Re: inverse gradient By: pgrigis on Tue, 02 December 2008 14:44
		Re: inverse gradient By: erano on Tue, 09 December 2008 00:36
		Re: inverse gradient By: erano on Wed, 24 December 2008 01:55

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