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!

You'll need OpenCV 2.3.1 installed.

Then:

    npm install opencv

Or to build the repo:

    node-gyp rebuild

    cv.readImage("./examples/test.jpg", function(err, im){
      im.detectObject(cv.FACE_CASCADE, {}, 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');
      });
    })

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

    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 ImageDataStream:

    var s = new cv.ImageDataStream()

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

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

If however, you have a series of images, and you wish to stream them into a stream of Matrices, you can use an ImageStream. Thus:

    var s = new cv.ImageStream()

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

    ardrone.createPngStream().pipe(s);

Note: Each 'data' event into the ImageStream should be a complete image buffer.

    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]

    mat.save('./pic.jpg')

or:

    var buff = mat.toBuffer()

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

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

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){})

For convenience in face recognition, cv.FACE_CASCADE is a cascade that can be used for frontal face recognition.

Also:

    mat.goodFeaturesToTrack

    mat.findCountours
    mat.drawContour
    mat.drawAllContours

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);

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

• V Early support for face recognition - API is likely to change. Have fun!
• API Change: VideoCapture.read now calls callback(err, im) instead of callback(im)

• Matrix clone()
• NamedWindow Support

• Bug Fixes
• ImageStream becomes ImageDataStream, and new ImageStream allows multiple images to be streamed as matrices, for example, with an object detection stream.
• @ryansouza improved documentation
• Correcting matrix constructor (thanks @gluxon)
• @Michael Smith expanded Contours functionality.

Thanks all!

• 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!

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