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Jorge Stolfi (talk | contribs) →Bogus theory?: Rewrote my earlier comments to describe correctly the problem and report my fixes. |
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==Removed passage on tensor addition==
I removed this paragraph and picture, since they do not seem to be understandable to readers who do not already know what they mean: "<nowiki>[[Image:TensorAddition.png|thumb|Tensor addition of sphere and step-edge case]]</nowiki>Another desirable property of the structure tensor form is that the tensor addition equates itself to the adding of the elliptical forms. For example, if the structure tensors for the sphere case and step-edge case are added, the resulting structure tensor is an elongated ellipsoid along the direction of the step-edge case.<br/>--[[User:Jorge Stolfi|Jorge Stolfi]] ([[User talk:Jorge Stolfi|talk]]) 06:26, 20 August 2010 (UTC)
== Can the coherence index be defined on uniform regions? ==
The coherence index was defined [http://en.wikipedia.org/w/index.php?title=Structure_tensor&oldid=368781876 in this version of the article] as 0 when the two eigenvalues were zero, that is, when the gradient was uniformly zero within the window. However, the formula for the general case does not have a definite limit when λ<sub>1</sub> and λ<sub>2</sub> both tend to 0, so any definition is equally wrong. Essentially, such a region can be regarded as totally isotropic or totally coherent, or anything in between, depending on what value one chooses to assign to 0/0.<br/> That article also tated that "[the coherence index] is capable of distinguishing between the isotropic and uniform cases." However, when λ<sub>1</sub> = λ<sub>2</sub> > 0, the first case of the definition yields 0, the same as the second case.<br/>pending clarification, I have removed this claim and merely noted that "some authord" define the index as 0 in the uniform case.<br/>--[[User:Jorge Stolfi|Jorge Stolfi]] ([[User talk:Jorge Stolfi|talk]]) 06:40, 20 August 2010 (UTC)
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