[Insight-users] Gradient Difference Metric

[Aviv Hurvitz]

I saw that in the docs.

In my opinion that bit, and the cited paper, are not enough for users to
understand what needs to be done. The fact is that it confused me, and
apparently others as well, and the cost of this confusion was big.

I suggested a few solutions:
1. Change the metric to go down.
2. Add a flag to all image metrics that says which way they go.
3. Clarify the metric direction in the docs.

You say #1 is impossible since it might break old code, and I agree.
(reluctantly... :)
#2 is best, I think, since it would allow both kinds of metrics to be
plugged into the same framework.
#3 is probably worst, because it would only solve the problem in this
particular metric, and it would still leave room for user errors.

Having read the code, I got the feeling that no one has used this metric
successfully. Sadly, I can't actually PROVE it now with a smoking gun. I'm
curious to know if there is any reader out there who uses this metric. I'm
not saying that we have a license to break it, I'm just giving you some
background about how I feel about this metric. In my opinion, it's not on
par with the rest of ITK, with regards to documentation, test cases, and
code quality.

I wish this thread wouldn't end with the conclusion that everything is
perfect just the way it is. Would someone please acknowledge that there is a
problem?

Regards,

- Aviv


On Thu, Jun 26, 2008 at 1:17 PM, Hauke Heibel <heibel at cs.tum.edu> wrote:

> Aviv Hurvitz wrote:
>
>> All the metrics I know in ITK go "down". There was no special
>> documentation, ...
>>
> As a matter of fact there is. Take a look at
> http://www.itk.org/Doxygen34/html/classitk_1_1GradientDifferenceImageToImageMetric.html
> It states "after passing the squared difference through a function of type
> 1/(1+x)".
>
> And I would not expect the functionality to change since there are many
> people who got the usage right and whose code would break if the class's
> functionality would change.
>
> - Hauke
>
> --
> Tim Hauke Heibel
> Computer Aided Medical Procedures (CAMP)
> fon: +49 89 289 19427
> fax: +49 89 289 17059
>
>
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