Android: Adaptive Thresholding

Question

I'm trying to implement adaptive thresholding algorithm by Derek Bradley using Android. But it is returning black pixels all the time. Here is my code snippet. Please suggest me about what should I do. Thanks in advance.

public static Bitmap GrayscaleToBin(Bitmap bm2)
{

    Bitmap bm;
    bm=bm2.copy(Config.ARGB_8888, true);
    final   int width = bm.getWidth();
    final  int height = bm.getHeight();
    int[]  pixels;
    pixels = new int[width*height];
    bm.getPixels(pixels,0,width,0,0,width,height);     
    //Bradley AdaptiveThrsholdging       
    int []intImg= new int[width*height];
    int sum=0;
    for(int i=0;i<width;++i){
        sum=0;
        for(int j=0;j<height;++j)
        {
            sum=sum+pixels[i+j*width];
            if(i==0){intImg[i+j*width]=sum;}
            else
            {
                intImg[i+j*width]= intImg[i-1+j*width]+sum;
            }
        }
    }
    int x1,x2,y1,y2=0,count=0;
    int s=width >> 3;   
    int t=15;
    for(int i=0;i<width;++i)
    {
        for(int j=0;j<height;++j)
        {
            x1=i-s/2;
            x2=i+s/2;
            y1=j-s/2;
            y2=j+s/2;
            if (x1 <0) x1 = 0;  
            if (x2>= width) x2 = width-1;  
            if (y1 <0) y1 = 0;  
            if (y2>= height) y2 = height-1;  
            count = (x2-x1) * (y2-y1);  
            sum = intImg [y2 * width + x2] -  
            intImg [y1 * width + x2] -  
            intImg [y2 * width + x1] +  
            intImg [y1 * width + x1]; 
            if((pixels[i+j*width]*count)<=(sum*(100-t)/100))
            {
                pixels[i+j*width]=0;
            }
            else
            {
                pixels[i+j*width]=255; 
            }
        }
    }
    /*---------------------------------------------------------------------------*/
    bm.setPixels(pixels,0,width,0,0,width,height);
    // Log.d("cdsfss","afterloop");
    return bm;
}

Answer 1

After a Long struggle I have solved the issue with the following code.

public static Bitmap GrayscaleToBin(Bitmap bm2)
 {
 Bitmap bm;
 bm=bm2.copy(Config.RGB_565, true);
 final   int width = bm.getWidth();
 final  int height = bm.getHeight();

 int pixel1,pixel2,pixel3,pixel4,A,R;
 int[]  pixels;
 pixels = new int[width*height];
 bm.getPixels(pixels,0,width,0,0,width,height);
 int size=width*height;
      int s=width/8;
      int s2=s>>1;
      double t=0.15;
      double it=1.0-t;
      int []integral= new int[size];
      int []threshold=new int[size];
      int i,j,diff,x1,y1,x2,y2,ind1,ind2,ind3;
      int sum=0;
      int ind=0;
      while(ind<size)
      {
       sum+=pixels[ind] & 0xFF;
       integral[ind]=sum;
       ind+=width;
      }
   x1=0;
   for(i=1;i<width;++i)       
   {
       sum=0;
       ind=i;
       ind3=ind-s2;
       if(i>s)
       {
           x1=i-s;
       }
       diff=i-x1;
       for(j=0;j<height;++j)
       {
           sum+=pixels[ind] & 0xFF;
           integral[ind]=integral[(int)(ind-1)]+sum;
           ind+=width;
           if(i<s2)continue;
           if(j<s2)continue;
           y1=(j<s ? 0 : j-s);
           ind1=y1*width;
           ind2=j*width;

        if (((pixels[ind3]&0xFF)*(diff * (j - y1))) < ((integral[(int)(ind2 + i)] - integral[(int)(ind1 + i)] - integral[(int)(ind2 + x1)] + integral[(int)(ind1 + x1)])*it)) {
            threshold[ind3] = 0x00;
        } else {
            threshold[ind3] = 0xFFFFFF;
        }
        ind3 += width;
    }
}

y1 = 0;
for( j = 0; j < height; ++j )
{
    i = 0;
    y2 =height- 1;
    if( j <height- s2 ) 
    {
        i = width - s2;
        y2 = j + s2;
    }

    ind = j * width + i;
    if( j > s2 ) y1 = j - s2;
    ind1 = y1 * width;
    ind2 = y2 * width;
    diff = y2 - y1;
    for( ; i < width; ++i, ++ind )
    {

        x1 = ( i < s2 ? 0 : i - s2);
        x2 = i + s2;

        // check the border
        if (x2 >= width) x2 = width - 1;

        if (((pixels[ind]&0xFF)*((x2 - x1) * diff)) < ((integral[(int)(ind2 + x2)] - integral[(int)(ind1 + x2)] - integral[(int)(ind2 + x1)] + integral[(int)(ind1 + x1)])*it)) {
            threshold[ind] = 0x00;
        } else {
            threshold[ind] = 0xFFFFFF;
        }
    }
}
   /*-------------------------------
    * --------------------------------------------*/
   bm.setPixels(threshold,0,width,0,0,width,height);

   return bm;
}

Answer 2

You can use Catalano Framework. There's an example using Bradley for Android in samples folder.

FastBitmap fb = new FastBitmap(bitmap);

fb.toGrayscale();

BradleyLocalThreshold bradley = new BradleyLocalThreshold();
bradley.applyInPlace(fb);

bitmap = fb.toBitmap();