Android: adaptive threshold

Question

I am trying to implement the adaptive threshold algorithm of Derek Bradley using Android. But he always returns black pixels. Here is my code snippet. Please suggest me what to 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=is/2; x2=i+s/2; y1=js/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 solved the problem 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=is; } 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 : js); 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 the Catalano Framework . Here is an example of using Bradley for Android in the sample folder.

 FastBitmap fb = new FastBitmap(bitmap); fb.toGrayscale(); BradleyLocalThreshold bradley = new BradleyLocalThreshold(); bradley.applyInPlace(fb); bitmap = fb.toBitmap();