Friday, March 2, 2012

Contour Refinement

In my hand tracking project I've used color segmentation to get the hand contour.
The problem is that usually the contour is not perfect, there are parts missing and/or there is some noise, for that reason I coded this general purpose contour refining function that fits the contour on a feature map moving each point along its normal.



Download file here

        /// <summary>
        /// Find better positions for each better at contour by searching on the edge normals on
        /// the feature map
        /// </summary>
        /// <param name="_objectContour">The contour to be refined</param>
        /// <param name="_featureMap">The feature map to be refined unto</param>
        /// <param name="_normalOffset">The maximum number of pixels to offset</param>
        /// <param name="_featureThreshold">The minimum feature value acceptable</param>
        /// <returns>Refined Contour</returns>
        public static Seq<Point> ContourRefine(
            Seq<Point> _objectContour,
            Image<Gray, float> _featureMap,
            int _normalOffset = 5,
            float _featureThreshold = float.MaxValue,
            float _inertiaCoeff = 1.0f,
            float _multiplierCoeff = -1.0f)
        {
            List<Point> pointsFitted = new List<Point>();
            Point[] pointsArray = _objectContour.ToArray();
            for (int i = 0; i < pointsArray.Length; i++)
            {
                int noPoints = pointsArray.Length,
                    ki = (i + 1) % noPoints, ik = (i >= 1) ? (i - 1) : (noPoints - 1 + i) % noPoints;
                Point pointCurrent = pointsArray[i],
                      pointNext = pointsArray[ki],
                      pointPrev = pointsArray[ik];
                // get normals pointing in and out
                PointF pointNormalOut = NormalAtPoint(pointPrev, pointCurrent, pointNext, false),
                    pointNormalIn = NormalAtPoint(pointPrev, pointCurrent, pointNext, true);
                // get points away from normal
                Point pointOut = new Point(
                        (int)Math.Round(pointNormalOut.X * _normalOffset) + pointCurrent.X,
                        (int)Math.Round(pointNormalOut.Y * _normalOffset) + pointCurrent.Y),
                    pointIn = new Point(
                        (int)Math.Round(pointNormalIn.X * _normalOffset) + pointCurrent.X,
                        (int)Math.Round(pointNormalIn.Y * _normalOffset) + pointCurrent.Y);
                LineSegment2D lineOut = new LineSegment2D(pointCurrent, pointOut),
                    lineIn = new LineSegment2D(pointCurrent, pointIn);

                // sample along the normals
                float[,] sampleIn = _featureMap.Sample(lineIn);
                float[,] sampleOut = _featureMap.Sample(lineOut);
                float maxByte = 0.0f, sample = 0.0f;
                int j = 0;
                bool inOut = false;
                // run through the normal pointing out to find the best fit
                for (int k = 0; k < sampleOut.Length; k++)
                {
                    sample = sampleOut[k, 0] + _multiplierCoeff * (float)Math.Pow(_inertiaCoeff, k);
                    if (sample > maxByte)
                    {
                        maxByte = sample;
                        j = k;
                        inOut = false;
                    }
                }

                // run through the normal pointing in to find the best fit
                for (int k = 0; k < sampleIn.Length; k++)
                {
                    sample = sampleIn[k, 0] + _multiplierCoeff * (float)Math.Pow(_inertiaCoeff, k);
                    if (sample > maxByte)
                    {
                        maxByte = sample;
                        j = k;
                        inOut = true;
                    }
                }

                // if feature on point found exceeds a threshold add it to the contour
                if (maxByte >= _featureThreshold)
                {
                    int x, y;
                    double length, xLength, yLength;
                    if (!inOut)
                    {
                        xLength = lineOut.P1.X - lineOut.P2.X;
                        yLength = lineOut.P1.Y - lineOut.P2.Y;
                        length = lineOut.Length;
                        x = (int)Math.Round((float)j / (float)sampleOut.Length * pointNormalOut.X * _normalOffset);
                        y = (int)Math.Round((float)j / (float)sampleOut.Length * pointNormalOut.Y * _normalOffset);
                    }
                    else
                    {
                        xLength = lineIn.P1.X - lineIn.P2.X;
                        yLength = lineIn.P1.Y - lineIn.P2.Y;
                        length = lineIn.Length;
                        x = (int)Math.Round((float)j / (float)sampleIn.Length * pointNormalIn.X * _normalOffset);
                        y = (int)Math.Round((float)j / (float)sampleIn.Length * pointNormalIn.Y * _normalOffset);
                    }
                    pointsFitted.Add(new Point(pointCurrent.X + x, pointCurrent.Y + y));
                }
            }
            _objectContour.Clear();
            _objectContour.PushMulti(pointsFitted.ToArray(), BACK_OR_FRONT.BACK);
            return _objectContour;
        }
        
        /// <summary>
        /// Calulcate the normal at given point
        /// </summary>
        /// <param name="_prevPoint">Previous point</param>
        /// <param name="_currentPoint">Current point</param>
        /// <param name="_nextPoint">Next point</param>
        /// <param name="_inOut">In or out flag</param>
        /// <returns>Normal at point</returns>
        public static PointF NormalAtPoint(
            Point _prevPoint, 
            Point _currentPoint, 
            Point _nextPoint, 
            bool _inOut = true)
        {
            PointF normal;
            float dx1 = _currentPoint.X - _prevPoint.X,
                  dx2 = _nextPoint.X - _currentPoint.X,
                  dy1 = _currentPoint.Y - _prevPoint.Y,
                  dy2 = _nextPoint.Y - _currentPoint.Y;
            if (_inOut)
                normal = new PointF((dy1 + dy2) * 0.5f, -(dx1 + dx2) * 0.5f);
            else
                normal = new PointF(-(dy1 + dy2) * 0.5f, (dx1 + dx2) * 0.5f);
            return NormalizePoint(normal);
        }
        
        /// <summary>
        /// Normalize a given point so its _noBinsAngle equals to one
        /// </summary>
        /// <param name="_point">Point to normalize</param>
        /// <returns>Normalized point</returns>
        public static PointF NormalizePoint(PointF _point)
        {
            float length = (float)Math.Sqrt(_point.X * _point.X + _point.Y * _point.Y);
            if (length > 0.0f)
                return new PointF(_point.X / length, _point.Y / length);
            return new PointF(0.0f, 0.0f);
        }

3 comments:

  1. Good Job Nikolas and thanks for the Blog.I am trying to implement a program like yours but in C++, could you please tell me where you got your information to do your program. Thanks in advance.

    ReplyDelete
  2. Would you please share very nice working practices muslumincedal@gmail.com

    ReplyDelete
  3. Would you please share very nice working practices joaorobertocotrim@gmail.com

    ReplyDelete

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