node-opencv/README.md

# node-opencv 

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[OpenCV](http://opencv.willowgarage.com/wiki/) 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:

```bash
$ npm install opencv
```

Or to build the repo:

```bash
$ node-gyp rebuild
```

## Examples

### Face Detection

```javascript
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');
  });
})
```


## API Documentation

### Matrix

The [matrix](http://opencv.jp/opencv-2svn_org/cpp/core_basic_structures.html#mat) is the most useful
base datastructure in OpenCV. Things like images are just matrices of pixels.

#### Creation

```javascript
new Matrix(rows, cols)
```

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

```javascript
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.

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

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

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

```javascript
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:

```javascript
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

```javascript
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

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

or:

```javascript
var buff = mat.toBuffer()
```

#### Image Processing

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


#### Simple Drawing

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

#### Object Detection

There is a shortcut method for 
[Viola-Jones Haar Cascade](http://www.cognotics.com/opencv/servo_2007_series/part_2/sidebar.html) object 
detection. This can be used for face detection etc.

```javascript
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:

```javascript
mat.goodFeaturesToTrack
```

#### Contours

```javascript
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](src/Contours.cc) and [examples](examples/)

```javascript
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

#### 0.5.0

Lots more opencv functions added, and bugfixes from a large number of
contributors. Thanks to all of them!

- Allow args for `HoughLinesP` by @clkao in #112
- `matchTemplate` and `minMaxLoc` by @ytham in #108
- updated `blockingWaitKey` by @hybridgroup in #98


#### 0.0.13 -> 0.4.0

( missing description... )

#### 0.0.13

- 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)

#### 0.0.12
- Matrix clone()
- NamedWindow Support

#### 0.0.11

- 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!

#### 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)