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N-dimensional find

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N-dimensional find

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26 May 2010 (Updated )

FIND_NDIM Finds the first or last nonzero element indices along a given matrix dimension.

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Description

This function finds the 'first' pixel in an N-dimensional image, along any dimension. This is somewhat like measuring from the top row of an image towards the bottom row of the image, and recording the first collision with an "on" pixel.

FIND_NDIM Finds first/last nonzero element indices along a dimension.
  I = FIND_NDIM(BW,DIM) returns the subscripts of the first nonzero
  elements of BW along the dimension DIM. Output I will contain zeros in
  element locations where no nonzero elements were found

  I = FIND_NDIM(BW,DIM,'first) is the same as I = FIND_NDIM(BW,DIM).

  I = FIND_NDIM(BW,DIM,'last') returns the subscripts of the last nonzero
  elements of BW along the dimension DIM.

  [I,MASK] = FIND_NDIM(BW,DIM,...) also returns a MASK the same size as
  BW with only the first/last pixels in dimension DIM on.

    Example 1:
        If X = [0 1 0
                  1 1 0]
        then find_ndim(X,1) returns [2 1 0], find_ndim(X,1,'last')
        returns [2 2 0], and find_ndim(X,2) returns [2 1]';

    Example 2:
        I = imread('rice.png');
        greyIm = imadjust(I - imopen(I,strel('disk',15)));
        BW = imclearborder(bwareaopen(im2bw(greyIm, graythresh(greyIm)), 50));
        topMostOnInds = find_ndim(BW, 1, 'first');
        rightMostOnInds = find_ndim(BW, 2, 'last');
        figure, imshow(BW), hold on
        plot(1:size(BW,2), topMostOnInds, 'r.')
        plot(rightMostOnInds, 1:size(BW,1), '.b')

A discussion of how this came about is at:
http://www.mathworks.com/matlabcentral/newsreader/view_thread/244823

MATLAB release MATLAB 7.10 (R2010a)
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Comments and Ratings (1)
12 Oct 2011 Joachim  
Updates
11 Oct 2011

Updated icon and help

20 Aug 2012

Added mask second output argument

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