quaggaJS/lib/frame_grabber.js

const CVUtils = require('../src/common/cv_utils'),
      Ndarray = require("ndarray"),
      Interp2D = require("ndarray-linear-interpolate").d2;

var FrameGrabber = {};

FrameGrabber.create = function(inputStream) {
    var _that = {},
        _streamConfig = inputStream.getConfig(),
        _video_size = CVUtils.imageRef(inputStream.getRealWidth(), inputStream.getRealHeight()),
        _canvasSize = inputStream.getCanvasSize(),
        _size = CVUtils.imageRef(inputStream.getWidth(), inputStream.getHeight()),
        _topRight = inputStream.getTopRight(),
        _data = new Uint8Array(_size.x * _size.y),
        _grayData = new Uint8Array(_video_size.x * _video_size.y),
        _canvasData = new Uint8Array(_canvasSize.x * _canvasSize.y),
        _grayImageArray = Ndarray(_grayData, [_video_size.y, _video_size.x]).transpose(1, 0),
        _canvasImageArray = Ndarray(_canvasData, [_canvasSize.y, _canvasSize.x]).transpose(1, 0),
        _targetImageArray = _canvasImageArray.hi(_topRight.x + _size.x, _topRight.y + _size.y).lo(_topRight.x, _topRight.y),
        _stepSizeX = _video_size.x/_canvasSize.x,
        _stepSizeY = _video_size.y/_canvasSize.y;

    console.log("FrameGrabber", JSON.stringify({
        videoSize: _grayImageArray.shape,
        canvasSize: _canvasImageArray.shape,
        stepSize: [_stepSizeX, _stepSizeY],
        size: _targetImageArray.shape,
        topRight: _topRight
    }));

    /**
     * Uses the given array as frame-buffer
     */
    _that.attachData = function(data) {
        _data = data;
    };

    /**
     * Returns the used frame-buffer
     */
    _that.getData = function() {
        return _data;
    };

    /**
     * Fetches a frame from the input-stream and puts into the frame-buffer.
     * The image-data is converted to gray-scale and then half-sampled if configured.
     */
    _that.grab = function() {
        var frame = inputStream.getFrame();

        if (frame) {
            this.scaleAndCrop(frame);
            return true;
        } else {
            return false;
        }
    };

    _that.scaleAndCrop = function(frame) {
        var x,
            y;

        // 1. compute full-sized gray image
        CVUtils.computeGray(frame.data, _grayData);

        // 2. interpolate
        for (y = 0; y < _canvasSize.y; y++) {
            for (x = 0; x < _canvasSize.x; x++) {
                _canvasImageArray.set(x, y, (Interp2D(_grayImageArray, x * _stepSizeX, y * _stepSizeY)) | 0);
            }
        }

        // targetImageArray must be equal to targetSize
        if (_targetImageArray.shape[0] !== _size.x ||
            _targetImageArray.shape[1] !== _size.y) {
            throw new Error("Shapes do not match!");
        }

        // 3. crop
        for (y = 0; y < _size.y; y++) {
            for (x = 0; x < _size.x; x++) {
                _data[y * _size.x + x] = _targetImageArray.get(x, y);
            }
        }
    },

    _that.getSize = function() {
        return _size;
    };

    return _that;
};

module.exports = FrameGrabber;