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May
25
comment What kind of algorithm can be used to map image coordinates to cylinder coordinates
@ChongVera: IIRC, I started with a simple 2nd order polynomial in X direction and 1st order polynomial in Y direction. Then I kept adding terms that didn't break FindMinimum and seemed to improve the result image visually. So, basically, by trial and error.
May
25
answered What kind of algorithm can be used to map image coordinates to cylinder coordinates
May
17
comment Compute a hessian matrix on a image?
@SURF: Of course, just pack the whole thing in a function that takes the scale parameter (second parameter to GaussianFilter) as a parameter and call that with a range of values (using Table or Array). Or use Manipulate to see the effect of scale interactively.
May
16
comment Compute a hessian matrix on a image?
@SURF: Sure, you could use e.g. minEigenvalue = MapThread[Min, imgEigenvalues, 2]; to calculate the per-pixel min of the two eigenvalues, then binarize the result that.
May
16
comment Compute a hessian matrix on a image?
@Histograms: As far as I understand the documentation, GradientFilter basically uses GaussianFilter, and it can only calculate the 1st derivative. You could use DerivativeFilter, of course. I generally start with GaussianFilter, as it's in some sense the most "natural" kernel and has (at least theoretically) certain unique advantages, especially if you calculate multiple scales. (The reasoning is too long for a comment, and honestly, I'd have to look most of it up myself, but I can give references if you're interested.)
May
16
answered Compute a hessian matrix on a image?
May
13
awarded  Nice Question
May
11
comment How to construct a kernel from a function?
Are you looking for Array or Table? Those evaluate a function resp. an expression for every cell in a matrix
May
4
awarded  Nice Answer
Apr
29
awarded  Nice Answer
Apr
29
answered Analyze touching particles with holes in a microscopic image
Apr
17
answered Integrating the second derivative of a 3D curve
Apr
15
comment Efficient way to perform local Otsu thresholding on image
as a workaround, you could calculate thresholds for every nth pixel, and interpolate in between.
Apr
7
revised cross point of intersecting lines
added 544 characters in body
Apr
7
answered cross point of intersecting lines
Apr
7
comment Looping within linear programming
Also, // does not start a comment in Mathematica code!
Apr
7
comment Looping within linear programming
This question would be much clearer if you posted the code that actually takes too much time. I've tried your first two code blocks, and neither takes more than a few milliseconds. Without that, the only tip that comes to mind is use FindMinimum instead of Minimize. Minimize tries to solve the problem symbolically, which is in general more expensive. FindMinimum uses local optimization, which is usually fastest, and for an LP is guaranteed to find the global minimum.
Apr
5
awarded  Guru
Apr
5
comment Is association in mathematica ordered or not?
@Nasser: It's not the most frequent use case, but sometimes you want to aggregate data in an Association, then later process the key/value pairs in the order they were discovered. And I often find it handy that BarChart, ListPlot&friends don't jumble association data I pass them. So I'm glad Wolfram made them ordered.
Apr
5
comment Ordered associations
Not exactly a reference, but Sort and KeySort return sorted associations (and that's documented behavior). That wouldn't make any sense if associations were unordered.