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POAndroid: Adaptive Thresholding
 

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    <p>I'm trying to implement adaptive thresholding algorithm by <a href="http://people.scs.carleton.ca/~roth/iit-publications-iti/docs/gerh-50002.pdf" rel="nofollow">Derek Bradley</a> 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.</p> <pre><code>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&lt;width;++i){ sum=0; for(int j=0;j&lt;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 &gt;&gt; 3; int t=15; for(int i=0;i&lt;width;++i) { for(int j=0;j&lt;height;++j) { x1=i-s/2; x2=i+s/2; y1=j-s/2; y2=j+s/2; if (x1 &lt;0) x1 = 0; if (x2&gt;= width) x2 = width-1; if (y1 &lt;0) y1 = 0; if (y2&gt;= 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)&lt;=(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; } </code></pre>
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    1. COThat paper deals with binarization, so my first issue with your code is the function's name "RGBtoGrayScale". That immediately raises another issue, the paper doesn't care about RGB images but your code doesn't seem to make sure the input is a grayscale one. Lastly, you are using a formula for finding the `s x s` average that is different from that on the paper (or any text that deals with integral images for the matter). Have you checked these issues ?
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    2. COsorry, Function name was not written properly. I've changed it. My input bitmap image is grayscale one and is obtained after grayscale from RGB conversion using R = G = B = (int)(0.299 * R + 0.587 * G + 0.114 * B); Again it is not working with s=width/8;
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