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# PtLists

Collection of PtList type

### Description

`PtLists` is the type used to store a collection of PtList objects.

Such objects are returned from shape analysis functions, such as findContours for example, which returns several lists of points, each of one for each detected contour.

`PtList` supports the extraction operator `(n:step:m)`, returning a single or a list of `PtList`, depending on the size of the interval.

`PtList` supports also the `size` function, returning the size of the list.

### Examples

    scicv_Init();

    img_gray = imread(getSampleImage("shapes.png"), CV_LOAD_IMAGE_GRAYSCALE);
    canny_img = Canny(img_gray, 100, 100*2, 3);

    [img_out, contours] = findContours(canny_img, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, [0, 0]);

    disp(typeof(contours));

    disp("Number of contours:");
    disp(size(contours));

### See also

- PtList

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