Apply Blur effect on Android, using Convolution Matrix

Last article describe the basic logic of Convolution Matrix, it's used to apply Blur effect on Bitmap.

- The Kernal used for blur is:
{1, 1, 1
  1, 1, 1
  1, 1, 1}

- There are 9 '1' in the Kernal, so we have to divid the sum of each pixel by 9, to make it in the save level.

- Each color is limited within the range of 0~255.

- To make the blur effect more obviously, the processingBitmap of blur is called 5 times.

package com.AndroidImageProcessing;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Color;
import android.os.Bundle;
import android.widget.ImageView;

public class AndroidImageProcessingActivity extends Activity {
 
 final static int KERNAL_WIDTH = 3;
 final static int KERNAL_HEIGHT = 3;
 
 int[][] kernalBlur ={
   {1, 1, 1},
   {1, 1, 1},
   {1, 1, 1}
 };
 
 int DIV_BY_9 = 9;
 
 ImageView imageSource, imageAfter;
 Bitmap bitmap_Source;
 
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        imageSource = (ImageView)findViewById(R.id.imageSource);
        imageAfter = (ImageView)findViewById(R.id.imageAfter);
        
        bitmap_Source = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher);
        
        Bitmap afterBlur = processingBitmap(bitmap_Source, kernalBlur);
        afterBlur = processingBitmap(afterBlur, kernalBlur);
        afterBlur = processingBitmap(afterBlur, kernalBlur);
        afterBlur = processingBitmap(afterBlur, kernalBlur);
        afterBlur = processingBitmap(afterBlur, kernalBlur);
        imageAfter.setImageBitmap(afterBlur);
    }
    
    private Bitmap processingBitmap(Bitmap src, int[][] knl){
     Bitmap dest = Bitmap.createBitmap(
       src.getWidth(), src.getHeight(), src.getConfig());
     
     int bmWidth = src.getWidth();
     int bmHeight = src.getHeight();
     int bmWidth_MINUS_2 = bmWidth - 2;
     int bmHeight_MINUS_2 = bmHeight - 2;
     
     for(int i = 1; i <= bmWidth_MINUS_2; i++){
      for(int j = 1; j <= bmHeight_MINUS_2; j++){
       
       //get the surround 3*3 pixel of current src[i][j] into a matrix subSrc[][]
       int[][] subSrc = new int[KERNAL_WIDTH][KERNAL_HEIGHT];
       for(int k = 0; k < KERNAL_WIDTH; k++){
        for(int l = 0; l < KERNAL_HEIGHT; l++){
         subSrc[k][l] = src.getPixel(i-1+k, j-1+l);
        }
       }
       
       //subSum = subSrc[][] * knl[][]
       int subSumA = 0;
       int subSumR = 0;
       int subSumG = 0;
       int subSumB = 0;

       for(int k = 0; k < KERNAL_WIDTH; k++){
        for(int l = 0; l < KERNAL_HEIGHT; l++){
         subSumA += Color.alpha(subSrc[k][l]) * knl[k][l];
         subSumR += Color.red(subSrc[k][l]) * knl[k][l];
         subSumG += Color.green(subSrc[k][l]) * knl[k][l];
         subSumB += Color.blue(subSrc[k][l]) * knl[k][l];
        }
       }
       
       subSumA = subSumA/DIV_BY_9;
       subSumR = subSumR/DIV_BY_9;
       subSumG = subSumG/DIV_BY_9;
       subSumB = subSumB/DIV_BY_9;
       
       if(subSumA<0){
        subSumA = 0;
       }else if(subSumA>255){
        subSumA = 255;
       }
       
       if(subSumR<0){
        subSumR = 0;
       }else if(subSumR>255){
        subSumR = 255;
       }
       
       if(subSumG<0){
        subSumG = 0;
       }else if(subSumG>255){
        subSumG = 255;
       }
       
       if(subSumB<0){
        subSumB = 0;
       }else if(subSumB>255){
        subSumB = 255;
       }

       dest.setPixel(i, j, Color.argb(
         subSumA, 
         subSumR, 
         subSumG, 
         subSumB));
      } 
     }
     
     return dest;
    }

}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/hello" />
    <ScrollView 
        android:layout_width="fill_parent"
        android:layout_height="fill_parent">
        <LinearLayout 
            android:layout_width="fill_parent"
         android:layout_height="fill_parent"
         android:orientation="vertical" >
         <TextView
             android:layout_width="fill_parent"
             android:layout_height="wrap_content"
             android:text="Original" />
      <ImageView
          android:id="@+id/imageSource" 
          android:layout_width="wrap_content"
          android:layout_height="wrap_content" 
          android:src="@drawable/ic_launcher"/>
      <TextView
             android:layout_width="fill_parent"
             android:layout_height="wrap_content"
             android:text="Result" />
      <ImageView
          android:id="@+id/imageAfter" 
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"/>
      
     </LinearLayout>
    </ScrollView>

</LinearLayout>

Related:
- Sharpen image, using Convolution Matrix

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