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CGSNAKE

CGSNAKE
  This program applies the Gradient Vector Flow active contour algorithm, as described by
  Chenyang Xu and Jerry L. Prince in "Snakes, Shapes, and Gradient Vector Flow" in the March
  1998 IEEE Transactions on Image Processing, Vol. 7, No.3. Additional information,
  including references to research papers, is available via Cheyang Xu's
  `web page <http://iacl.ece.jhu.edu/projects/gvf/>`.
  Active contours are often described as "snakes" because they writhe and move
  under the influence of external and internal forces, toward a feature of interest
  in an image, usually an edge. This program gives the user the opportunity
  to control both external and internal forces to find an optimal set of active contour
  parameters. Active contours are most often used with images to find and describe
  regions of interest.
 
  This program requires the GVF_Snake object, which can be purchased at the
  `Coyote Store <http://www.idlcoyote.com/coyotestore/index.php>`.

Categories


    Image Processing
   

Returns


    The function returns an ROI structure containing the deformed points of the final contour
    in addition to other information. The return structure looks like this::
   
        roiStruct = { npts: 0L ; The length of the X and Y fields in the structure.
                      x: 0.0 ; The X values (in image coordinates) of the final contour.
                      y: 0.0 ; The Y values (in image coordinates) of the final contour.
                      perimeter: 0.0 ; The perimenter length of the ROI.
                      area: 0.0 ; The area enclosed by the ROI.
                      values: ; A vector of length npts, giving the value of the image at (x,y).
                    }

Author


    FANNING SOFTWARE CONSULTING::
      David W. Fanning
      1645 Sheely Drive
      Fort Collins, CO 80526 USA
      Phone: 970-221-0438
      E-mail: david@idlcoyote.com
      Coyote's Guide to IDL Programming: http://www.idlcoyote.com

Params


    image: in, required
        The image for which the active contour (snake) will be applied.
        This argument must be 2D. The user will be asked to select an
        image file if this argument is not provided.
    x_init: in, required, type=float
        The initial X points of the active contour or snake. Must be paired with Y.
        Assume values are pixel locations within image.
    y_init: in, required, type=float
        The initial Y points of the active contour or snake. Must be paired with X.
        Assume values are pixel locations within image.
     

Keywords


    alpha: in, optional, type=float, default=0.10
        The elasticity parameter of the active contour. It reflects the contour's
        ability to stretch along its length.
    beta: in, optional, type=float, default=0.25
        The rigidity parameter of the active contour. It reflects the contour's
        ability to bend, as, for example, around corners.
    blur: in, optional, type=boolean, default=1
        Set this keyword to 1 if you want a Gaussian Blur applied to image before
        processing. Set it to 0 otherwise.
    delta_max: in, optional, type=float, default=5.50
        The maximum pixel distance for adaptive interpolation.
    delta_min: in, optional, type=float, default=0.25
        The minimum pixel distance for adaptive interpolation.
    gamma: in, optional, type=float, default=1.0
        The viscosity parameter. Larger values make it harder to deform the active
        contour in space.
    gradientscale: in, optional, type=float, default=1.75
        A multiplication factor for the gradient calculations.
    kappa: in, optional, type=float, default=1.25
        The external force weight.
    gvf_iterations: in, optional, type=integer, default=30
        The number of iterations for calculating the Gradient Vector Flow (GVF).
    iterations: in, optional, type=integer, default=120
        The number of iterations to use in calculating the snake positions.
    max_value: in, optional, type=varies
        The maximum value for scaling the image data to create contrast for the edge mask.
    min_value: in, optional, type=varies
        The minimum value for scaling the image data to create contrast for the edge mask.
    mu: in, optional, type=float, default=0.10
        The regularization parameter. This should be set according to the amount of
        noise in the image. Use a larger value for noisier images.
    parameterfile: in, optional, type=string
        The name of a parameter file created with the ActiveContour program and containing
        most of the snake parameters set here with other keywords.
    sigma: in, optional, type=float, default=1.0
        The standard deviation or sigma of the Gaussian function used in Gaussian
        blurring.
    spatial_scale: in, optional, type=double, default=1.0D
        Set this keyword to a two-element array that specifies the pixel scale in
        the X and Y directions ([xscale, yscale]). The scale factors are applied
        when the perimeter and area calculations for the final contour is made.
        Default is [1.0D, 1.0D].

History


Modification History


      Written by David W. Fanning, 25 October 2013, based on ActiveContour program from 2003.

Copyright


    Copyright (c) 2013, Fanning Software Consulting, Inc.



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