AdaptiveThreshold.cs

using IdApp.Cv.Statistics;
using System;
 
namespace IdApp.Cv.Transformations.Thresholds
{
    public static partial class TransformationOperations
    {
        public static void AdaptiveThreshold(this Matrix<float> M, float Threshold,
            int NeighborhoodWidth)
        {
            if (NeighborhoodWidth <= 0 || NeighborhoodWidth >= M.Width || NeighborhoodWidth >= M.Height)
                throw new ArgumentOutOfRangeException(nameof(NeighborhoodWidth));
 
            Matrix<float> Integral = M.Integral();
 
            int From = -NeighborhoodWidth / 2;
            int To = NeighborhoodWidth + From;
            int y, h = M.Height;
            int x, w = M.Width;
            int Index = M.Start;
            int Skip = M.Skip;
            float[] Data = M.Data;
            float[] Sums = Integral.Data;
            float v, Avg;
            int x1, y1, x2, y2, dx, dy;
 
            for (y = 0; y < h; y++, Index += Skip)
            {
                y1 = y + From;
                if (y1 < 0)
                    y1 = 0;
 
                y2 = y + To;
                if (y2 >= h)
                    y2 = h - 1;
 
                dy = y2 - y1;
 
                for (x = 0; x < w; x++)
                {
                    x1 = x + From;
                    if (x1 < 0)
                        x1 = 0;
 
                    x2 = x + To;
                    if (x2 >= w)
                        x2 = w - 1;
 
                    dx = x2 - x1;
 
                    v = Data[Index];
                    Avg = (Sums[x2 + y2 * w] - Sums[x1 + y2 * w] - Sums[x2 + y1 * w] + Sums[x1 + y1 * w]) / (dx * dy);
 
                    Data[Index++] = v <= Avg - Threshold ? 0f : 1f;
                }
            }
        }
 
        public static void AdaptiveThreshold(this Matrix<int> M, int Threshold,
            int NeighborhoodWidth)
        {
            if (NeighborhoodWidth <= 0 || NeighborhoodWidth >= M.Width || NeighborhoodWidth >= M.Height)
                throw new ArgumentOutOfRangeException(nameof(NeighborhoodWidth));
 
            Matrix<long> Integral = M.Integral();
 
            int From = -NeighborhoodWidth / 2;
            int To = NeighborhoodWidth + From;
            int y, h = M.Height;
            int x, w = M.Width;
            int Index = M.Start;
            int Skip = M.Skip;
            int[] Data = M.Data;
            long[] Sums = Integral.Data;
            int v, Avg;
            int x1, y1, x2, y2, dx, dy, dxdy;
 
            for (y = 0; y < h; y++, Index += Skip)
            {
                y1 = y + From;
                if (y1 < 0)
                    y1 = 0;
 
                y2 = y + To;
                if (y2 >= h)
                    y2 = h - 1;
 
                dy = y2 - y1;
 
                for (x = 0; x < w; x++)
                {
                    x1 = x + From;
                    if (x1 < 0)
                        x1 = 0;
 
                    x2 = x + To;
                    if (x2 >= w)
                        x2 = w - 1;
 
                    dx = x2 - x1;
                    dxdy = dx * dy;
 
                    v = Data[Index];
                    Avg = (int)((Sums[x2 + y2 * w] - Sums[x1 + y2 * w] - Sums[x2 + y1 * w] + Sums[x1 + y1 * w] + (dxdy >> 1)) / dxdy);
 
                    Data[Index++] = v <= Avg - Threshold ? 0 : 0x01000000;
                }
            }
        }
    }
}