Uses the multiresolution wavelet analysis to extract the edges of a signal.


icon

Inputs/Outputs

  • c2ddbl.png signal —

    signal specifies the 2D input signal.

  • cdbl.png threshold ratio —

    threshold ratio specifies the relative threshold to use to reject small peaks. threshold ratio is defined in the range [0, 1], where 0 and 1 correspond to the minimum and maximum values of the coefficients, respectively. The smaller the value of threshold ratio, the more edges this VI detects.

  • ci32.png levels —

    levels specifies the number of levels in the discrete wavelet analysis. levels must be a positive integer no greater than log2(Ls), where Ls is the length of the 1D signal or the minimum dimensional size of the 2D signal. The default is -1, which indicates that this VI sets levels as the largest integer no greater than log2(Ls).

  • cerrcodeclst.png error in (no error) —

    error in describes error conditions that occur before this node runs. This input provides standard error in functionality.

  • i1dcclst.png edges —

    edges returns the detected edges at different levels. The ith element of edges contains the edges of signal at the (i+1)th level. The edges at smaller levels reveal the details of the image, and the edges at larger levels provide the global and large-scale edges of the image, for example, the contour of an image.

  • i2du8.png edge —

    edge returns the edge of a level. edge is a binary image. 1 indicates that this VI detects an edge. You can display edge on an intensity graph or with the WA Gray Scale Image control.

  • ierrcodeclst.png error out —

    error out contains error information. This output provides standard error out functionality.

    • WA Multiscale Edge Detection Details

    Usually, the modulus-maxima of the detail coefficients of signal corresponds to the edge of signal. This VI completes the following steps to implement the multi-scale edge detection.

    1. Performs the undecimated wavelet transform with wavelet bior3_1 on the rows and the columns, respectively, at each level. Obtains the detail coefficients along the row direction and the column direction . (i, j) denotes the row and column index of the matrix, respectively.
    2. Computes a new matrix Rl with the formula .
    3. Finds the local maxima of Rl as the edge points at level l.

    Refer to A Wavelet Tour of Signal Processing for more information about multi-scale edge detection.

    Examples

    Refer to the Image Edge Detection VI in the labview\examples\Wavelet Analysis\WAApplications directory for an example of using the WA Multiscale Edge Detection VI.