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OpenCV Bindings for node.js

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README.md

node-opencv

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OpenCV bindings for Node.js. OpenCV is the defacto computer vision library - by interfacing with it natively in node, we get powerful real time vision in js.

People are using node-opencv to fly control quadrocoptors, detect faces from webcam images and annotate video streams. If you're using it for something cool, I'd love to hear about it!

Install

You'll need OpenCV 2.3.1 installed.

Then:

    npm install opencv

Or to build the repo:

    node-gyp rebuild

Examples

Face Detection

    cv.readImage("./examples/test.jpg", function(err, im){
      im.detectObject("./data/haarcascade_frontalface_alt.xml", {}, function(err, faces){
        for (var i=0;i<faces.length; i++){
          var x = faces[i]
          im.ellipse(x.x + x.width/2, x.y + x.height/2, x.width/2, x.height/2);
        }
        im.save('./out.jpg');
      });
    })

API Documentation

Matrix

The matrix is the most useful base datastructure in OpenCV. Things like images are just matrices of pixels.

Creation

    new Matrix(rows, cols)

Or if you're thinking of a Matrix as an image:

    new Matrix(height, width)

Or you can use opencv to read in image files. Supported formats are in the OpenCV docs, but jpgs etc are supported.

    cv.readImage(filename, function(mat){
      ...
    })

    cv.readImage(buffer, function(mat){
      ...
    })

If you need to pipe data into an image, you can use an imagestream:

    var s = new cv.ImageStream()

    s.on('load', function(matrix){ 
      ...
    }) 

    fs.createReadStream('./examples/test.jpg').pipe(s);        

Accessing Data

    var mat = new cv.Matrix.Eye(4,4); // Create identity matrix

    mat.get(0,0) // 1

    mat.row(0)  // [1,0,0,0]
    mat.col(4)  // [0,0,0,1]
Save
    mat.save('./pic.jpg')

or:

    var buff = mat.toBuffer()

Image Processing

    im.convertGrayscale()
    im.canny(5, 300)
    im.houghLinesP()

Simple Drawing

    im.ellipse(x, y)
    im.line([x1,y1], [x2, y2])

Object Detection

There is a shortcut method for Viola-Jones Haar Cascade object detection. This can be used for face detection etc.

    mat.detectObject(haar_cascade_xml, opts, function(err, matches){})

Also:

    mat.goodFeaturesToTrack

Contours

    mat.findCountours
    mat.drawContour
    mat.drawAllContours

Using Contours

findContours returns a Contours collection object, not a native array. This object provides functions for accessing, computing with, and altering the contours contained in it. See relevant source code and examples

    var contours = im.findContours;

    # Count of contours in the Contours object
    contours.size();

    # Count of corners(verticies) of contour `index`
    contours.cornerCount(index);

    # Access vertex data of contours
    for(var c = 0; c < contours.size(); ++c) {
      console.log("Contour " + c);
      for(var i = 0; i < contours.cornerCount(c); ++i) {
        var point = contours.point(c, i);
        console.log("(" + point.x + "," + point.y + ")");"
      }
    }

    # Computations of contour `index`
    contours.area(index);
    contours.arcLength(index, isClosed);
    contours.boundingRect(index);
    contours.minAreaRect(index);
    contours.isConvex(index);

    # Destructively alter contour `index`
    contours.approxPolyDP(index, epsilon, isClosed);
    contours.convexHull(index, clockwise);

MIT License

The library is distributed under the MIT License - if for some reason that doesn't work for you please get in touch.

Changelog

0.0.10

  • Bug Fixes
  • @Contra added code that allows thickness and color args for ellipse
  • Camshift Support
  • @jtlebi added bindings for erode, gaussianBlur, arcLength, approxPolyDP, isConvex, cornerCount
  • @gluxon added bindings for inRange

Thanks everyone!

0.0.9

  • toBuffer can now take a callback and be run async (re #21)
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