node-opencv
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 or newer installed before installing node-opencv. Note
that OpenCV 3.x is not yet fully supported.
Specific for Windows
-
Download and install OpenCV (Be sure to use a 2.4 version) @
http://opencv.org/downloads.html
For these instructions we will assume OpenCV is put at C:\OpenCV, but you can
adjust accordingly.
-
If you haven't already, create a system variable called OPENCV_DIR and set it
to C:\OpenCV\build\x64\vc12
Make sure the "x64" part matches the version of NodeJS you are using.
Also add the following to your system PATH
;%OPENCV_DIR%\bin
-
Install Visual Studio 2013. Make sure to get the C++ components.
You can use a different edition, just make sure OpenCV supports it, and you
set the "vcxx" part of the variables above to match.
-
Download peterbraden/node-opencv fork
git clone https://github.com/peterbraden/node-opencv
-
run npm install
$ npm install opencv
Examples
Run the examples from the parent directory.
Face Detection
cv.readImage("./examples/files/mona.png", 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');
});
})
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(err, mat){
...
})
cv.readImage(buffer, function(err, 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/files/mona.png').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.
Accessing Data
var mat = new cv.Matrix.Eye(4,4);
mat.get(0,0)
mat.row(0)
mat.col(4)
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){})
For convenience in face detection, cv.FACE_CASCADE is a cascade that can be used for frontal face detection.
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();
contours.size();
contours.cornerCount(index);
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 + ")");
}
}
contours.area(index);
contours.arcLength(index, isClosed);
contours.boundingRect(index);
contours.minAreaRect(index);
contours.isConvex(index);
contours.fitEllipse(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.