:param array:Raster image (single-channel, 8-bit or floating-point 2D array) or an array ( :math:`1 \times N` or :math:`N \times 1` ) of 2D points (``Point`` or ``Point2f`` ).
The function computes moments, up to the 3rd order, of a vector shape or a rasterized shape. The results are returned in the structure ``Moments`` defined as: ::
:math:`\texttt{nu}_{10}=\texttt{mu}_{10}=\texttt{mu}_{01}=\texttt{mu}_{10}=0` , hence the values are not stored.
The moments of a contour are defined in the same way but computed using the Green's formula (see http://en.wikipedia.org/wiki/Green_theorem). So, due to a limited raster resolution, the moments computed for a contour are slightly different from the moments computed for the same rasterized contour.
Since the contour moments are computed using Green formula, you may get seemingly odd results for contours with self-intersections, e.g. a zero area (``m00``) for butterfly-shaped contours.
These values are proved to be invariants to the image scale, rotation, and reflection except the seventh one, whose sign is changed by reflection. This invariance is proved with the assumption of infinite image resolution. In case of raster images, the computed Hu invariants for the original and transformed images are a bit different.
..ocv:function:: void findContours( InputOutputArray image, OutputArrayOfArrays contours, OutputArray hierarchy, int mode, int method, Point offset=Point())
..ocv:cfunction:: int cvFindContours( CvArr* image, CvMemStorage* storage, CvSeq** first_contour, int header_size=sizeof(CvContour), int mode=CV_RETR_LIST, int method=CV_CHAIN_APPROX_SIMPLE, CvPoint offset=cvPoint(0,0) )
:param image:Source, an 8-bit single-channel image. Non-zero pixels are treated as 1's. Zero pixels remain 0's, so the image is treated as ``binary`` . You can use :ocv:func:`compare` , :ocv:func:`inRange` , :ocv:func:`threshold` , :ocv:func:`adaptiveThreshold` , :ocv:func:`Canny` , and others to create a binary image out of a grayscale or color one. The function modifies the ``image`` while extracting the contours.
:param hierarchy:Optional output vector, containing information about the image topology. It has as many elements as the number of contours. For each i-th contour ``contours[i]`` , the elements ``hierarchy[i][0]`` , ``hiearchy[i][1]`` , ``hiearchy[i][2]`` , and ``hiearchy[i][3]`` are set to 0-based indices in ``contours`` of the next and previous contours at the same hierarchical level, the first child contour and the parent contour, respectively. If for the contour ``i`` there are no next, previous, parent, or nested contours, the corresponding elements of ``hierarchy[i]`` will be negative.
***CV_RETR_CCOMP** retrieves all of the contours and organizes them into a two-level hierarchy. At the top level, there are external boundaries of the components. At the second level, there are boundaries of the holes. If there is another contour inside a hole of a connected component, it is still put at the top level.
***CV_RETR_TREE** retrieves all of the contours and reconstructs a full hierarchy of nested contours. This full hierarchy is built and shown in the OpenCV ``contours.c`` demo.
***CV_CHAIN_APPROX_NONE** stores absolutely all the contour points. That is, any 2 subsequent points ``(x1,y1)`` and ``(x2,y2)`` of the contour will be either horizontal, vertical or diagonal neighbors, that is, ``max(abs(x1-x2),abs(y2-y1))==1``.
***CV_CHAIN_APPROX_SIMPLE** compresses horizontal, vertical, and diagonal segments and leaves only their end points. For example, an up-right rectangular contour is encoded with 4 points.
***CV_CHAIN_APPROX_TC89_L1,CV_CHAIN_APPROX_TC89_KCOS** applies one of the flavors of the Teh-Chin chain approximation algorithm. See [TehChin89]_ for details.
:param offset:Optional offset by which every contour point is shifted. This is useful if the contours are extracted from the image ROI and then they should be analyzed in the whole image context.
..note:: Source ``image`` is modified by this function. Also, the function does not take into account 1-pixel border of the image (it's filled with 0's and used for neighbor analysis in the algorithm), therefore the contours touching the image border will be clipped.
..note:: If you use the new Python interface then the ``CV_`` prefix has to be omitted in contour retrieval mode and contour approximation method parameters (for example, use ``cv2.RETR_LIST`` and ``cv2.CHAIN_APPROX_NONE`` parameters). If you use the old Python interface then these parameters have the ``CV_`` prefix (for example, use ``cv.CV_RETR_LIST`` and ``cv.CV_CHAIN_APPROX_NONE``).
..ocv:function:: void drawContours( InputOutputArray image, InputArrayOfArrays contours, int contourIdx, const Scalar& color, int thickness=1, int lineType=8, InputArray hierarchy=noArray(), int maxLevel=INT_MAX, Point offset=Point() )
:param contours:All the input contours. Each contour is stored as a point vector.
:param contourIdx:Parameter indicating a contour to draw. If it is negative, all the contours are drawn.
:param color:Color of the contours.
:param thickness:Thickness of lines the contours are drawn with. If it is negative (for example, ``thickness=CV_FILLED`` ), the contour interiors are
drawn.
:param lineType:Line connectivity. See :ocv:func:`line` for details.
:param hierarchy:Optional information about hierarchy. It is only needed if you want to draw only some of the contours (see ``maxLevel`` ).
:param maxLevel:Maximal level for drawn contours. If it is 0, only
the specified contour is drawn. If it is 1, the function draws the contour(s) and all the nested contours. If it is 2, the function draws the contours, all the nested contours, all the nested-to-nested contours, and so on. This parameter is only taken into account when there is ``hierarchy`` available.
:param offset:Optional contour shift parameter. Shift all the drawn contours by the specified :math:`\texttt{offset}=(dx,dy)` .
:param contour:Pointer to the first contour.
:param externalColor:Color of external contours.
:param holeColor:Color of internal contours (holes).
The function draws contour outlines in the image if
:math:`\texttt{thickness} \ge 0` or fills the area bounded by the contours if
:math:`\texttt{thickness}<0` . The example below shows how to retrieve connected components from the binary image and label them:::
#include "cv.h"
#include "highgui.h"
using namespace cv;
int main( int argc, char** argv )
{
Mat src;
// the first command-line parameter must be a filename of the binary
// (black-n-white) image
if( argc != 2 || !(src=imread(argv[1], 0)).data)
return -1;
Mat dst = Mat::zeros(src.rows, src.cols, CV_8UC3);
src = src > 1;
namedWindow( "Source", 1 );
imshow( "Source", src );
vector<vector<Point> > contours;
vector<Vec4i> hierarchy;
findContours( src, contours, hierarchy,
CV_RETR_CCOMP, CV_CHAIN_APPROX_SIMPLE );
// iterate through all the top-level contours,
// draw each connected component with its own random color
:param approxCurve:Result of the approximation. The type should match the type of the input curve. In case of C interface the approximated curve is stored in the memory storage and pointer to it is returned.
:param recursive:Recursion flag. If it is non-zero and ``curve`` is ``CvSeq*``, the function ``cvApproxPoly`` approximates all the contours accessible from ``curve`` by ``h_next`` and ``v_next`` links.
The functions ``approxPolyDP`` approximate a curve or a polygon with another curve/polygon with less vertices so that the distance between them is less or equal to the specified precision. It uses the Douglas-Peucker algorithm
:param minimal_perimeter:Approximates only those contours whose perimeters are not less than ``minimal_perimeter`` . Other chains are removed from the resulting structure.
:param recursive:Recursion flag. If it is non-zero, the function approximates all chains that can be obtained from ``chain`` by using the ``h_next`` or ``v_next`` links. Otherwise, the single input chain is approximated.
This is a standalone contour approximation routine, not represented in the new interface. When :ocv:cfunc:`FindContours` retrieves contours as Freeman chains, it calls the function to get approximated contours, represented as polygons.
:param oriented:Oriented area flag. If it is true, the function returns a signed area value, depending on the contour orientation (clockwise or counter-clockwise). Using this feature you can determine orientation of a contour by taking the sign of an area. By default, the parameter is ``false``, which means that the absolute value is returned.
:ocv:func:`moments` , the area is computed using the Green formula. Thus, the returned area and the number of non-zero pixels, if you draw the contour using
:param hull:Output convex hull. It is either an integer vector of indices or vector of points. In the first case, the ``hull`` elements are 0-based indices of the convex hull points in the original array (since the set of convex hull points is a subset of the original point set). In the second case, ``hull`` elements are the convex hull points themselves.
:param clockwise:Orientation flag. If it is true, the output convex hull is oriented clockwise. Otherwise, it is oriented counter-clockwise. The assumed coordinate system has its X axis pointing to the right, and its Y axis pointing upwards.
:param returnPoints:Operation flag. In case of a matrix, when the flag is true, the function returns convex hull points. Otherwise, it returns indices of the convex hull points. When the output array is ``std::vector``, the flag is ignored, and the output depends on the type of the vector: ``std::vector<int>`` implies ``returnPoints=true``, ``std::vector<Point>`` implies ``returnPoints=false``.
*O(N logN)* complexity in the current implementation. See the OpenCV sample ``convexhull.cpp`` that demonstrates the usage of different function variants.
:param convexityDefects:The output vector of convexity defects. In C++ and the new Python/Java interface each convexity defect is represented as 4-element integer vector (a.k.a. ``cv::Vec4i``): ``(start_index, end_index, farthest_pt_index, fixpt_depth)``, where indices are 0-based indices in the original contour of the convexity defect beginning, end and the farthest point, and ``fixpt_depth`` is fixed-point approximation (with 8 fractional bits) of the distance between the farthest contour point and the hull. That is, to get the floating-point value of the depth will be ``fixpt_depth/256.0``. In C interface convexity defect is represented by ``CvConvexityDefect`` structure - see below.
The function finds all convexity defects of the input contour and returns a sequence of the ``CvConvexityDefect`` structures, where ``CvConvexityDetect`` is defined as: ::
struct CvConvexityDefect
{
CvPoint* start; // point of the contour where the defect begins
CvPoint* end; // point of the contour where the defect ends
CvPoint* depth_point; // the farthest from the convex hull point within the defect
float depth; // distance between the farthest point and the convex hull
The function calculates the ellipse that fits (in a least-squares sense) a set of 2D points best of all. It returns the rotated rectangle in which the ellipse is inscribed. The algorithm [Fitzgibbon95]_ is used.
:param line:Output line parameters. In case of 2D fitting, it should be a vector of 4 elements (like ``Vec4f``) - ``(vx, vy, x0, y0)``, where ``(vx, vy)`` is a normalized vector collinear to the line and ``(x0, y0)`` is a point on the line. In case of 3D fitting, it should be a vector of 6 elements (like ``Vec6f``) - ``(vx, vy, vz, x0, y0, z0)``, where ``(vx, vy, vz)`` is a normalized vector collinear to the line and ``(x0, y0, z0)`` is a point on the line.
The function tests whether the input contour is convex or not. The contour must be simple, that is, without self-intersections. Otherwise, the function output is undefined.
The function calculates and returns the minimum-area bounding rectangle (possibly rotated) for a specified point set. See the OpenCV sample ``minarea.cpp`` .
:param measureDist:If true, the function estimates the signed distance from the point to the nearest contour edge. Otherwise, the function only checks if the point is inside a contour or not.
..[Fitzgibbon95] Andrew W. Fitzgibbon, R.B.Fisher. *A Buyer's Guide to Conic Fitting*. Proc.5th British Machine Vision Conference, Birmingham, pp. 513-522, 1995.
