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Using Hough Transform

May 30, 2017 8:13 AM
(7377 views)

Hi,

I want to use the Hough tranform function in a program I am writing to detect edges, however I am a little confused by what values the input matrix should contain. I tried using the scripting index but it wasn't particularly helpful. Is the matrix the matrix of rgb values, hsl values, or a column vector of intensity values? Thanks!

Noah

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Re: Using Hough Transform

Hi, Noah.

The JSL Syntax Reference has a little more information on this function than the Scripting Index. There is says that "it takes a matrix of intensities and transforms it in a way that is useful for finding streaks in the matrix."

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Re: Using Hough Transform

Not answering your question, but I did find this explanation of the transform

Craige

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Re: Using Hough Transform

Created:
May 31, 2017 7:05 AM
| Last Modified: May 31, 2017 7:13 AM
(7342 views)
| Posted in reply to message from Craige_Hales 05-31-2017

Here's what I've learned:

the input matrix is an approximately square matrix of non-negative values that are accumulated into the output using the transform. I believe the transform is actually the sin/cos variation described at the end of the video. There are two parameters you can use in the function call:

HoughLineTransform( M, NAngle(180), NRadius( r) )

specified by name, after the matrix. 180 is the default number of angles and is the number of columns in the output matrix. "r" defaults to sqrt(nr^2+nc^2), roughly the diagonal "pixels" of the matrix, and is the number of rows in the output matrix.

I'd also suggest looking at the canny filter in the scripting index; it has a very cool example (2nd example under filter).

Craige

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Re: Using Hough Transform

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