Convert bitmap from color to GrayScale

Last article described how to Convert bitmap from color to black and white using the simple formula BW = (R + G +)/3. Some experts suggested that it should be 0.3R + 0.59G + 0.11B ~ refer http://en.wikipedia.org/wiki/Grayscale.

Copy your test picture to /res/drawable folder, name it testpicture.jpg.

package com.AndroidBitmapProcessing;

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 AndroidBitmapProcessingActivity extends Activity {
 
 ImageView imageView_Source, imageView_Gray, imageView_BW;
 Bitmap bitmap_Source, bitmap_Dest;
 
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        imageView_Source = (ImageView)findViewById(R.id.source);
        imageView_Gray = (ImageView)findViewById(R.id.imageGray);
        imageView_BW = (ImageView)findViewById(R.id.imageBW);
        
        bitmap_Source = BitmapFactory.decodeResource(getResources(), R.drawable.testpicture);
        imageView_Gray.setImageBitmap(processingBitmap_Gray(bitmap_Source));
        imageView_BW.setImageBitmap(processingBitmap_BW(bitmap_Source));
    }
    
    private Bitmap processingBitmap_Gray(Bitmap src){
     
     Bitmap dest = Bitmap.createBitmap(
       src.getWidth(), src.getHeight(), src.getConfig());
     
     for(int x = 0; x < src.getWidth(); x++){
      for(int y = 0; y < src.getHeight(); y++){
       int pixelColor = src.getPixel(x, y);
       int pixelAlpha = Color.alpha(pixelColor);
       float pixelRed = (float)Color.red(pixelColor) * 0.3f;
       float pixelGreen = (float)Color.green(pixelColor) * 0.59f;
       float pixelBlue = (float)Color.blue(pixelColor) * 0.11f;
       
       int pixelBW = (int)(pixelRed + pixelGreen + pixelBlue);
       int newPixel = Color.argb(
         pixelAlpha, pixelBW, pixelBW, pixelBW);
       
       dest.setPixel(x, y, newPixel);
      }
     }
     
     return dest;
    }
    
    private Bitmap processingBitmap_BW(Bitmap src){
     
     Bitmap dest = Bitmap.createBitmap(
       src.getWidth(), src.getHeight(), src.getConfig());
     
     for(int x = 0; x < src.getWidth(); x++){
      for(int y = 0; y < src.getHeight(); y++){
       int pixelColor = src.getPixel(x, y);
       int pixelAlpha = Color.alpha(pixelColor);
       int pixelRed = Color.red(pixelColor);
       int pixelGreen = Color.green(pixelColor);
       int pixelBlue = Color.blue(pixelColor);
       
       int pixelBW = (pixelRed + pixelGreen + pixelBlue)/3;
       int newPixel = Color.argb(
         pixelAlpha, pixelBW, pixelBW, pixelBW);
       
       dest.setPixel(x, y, newPixel);
      }
     }
     
     return dest;
    }
}

main.xml

<?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/source" 
          android:layout_width="wrap_content"
          android:layout_height="wrap_content" 
          android:src="@drawable/testpicture"/>
      <TextView
             android:layout_width="fill_parent"
             android:layout_height="wrap_content"
             android:text="Gray: 0.3R + 0.59G + 0.11B" />
      <ImageView
          android:id="@+id/imageGray" 
          android:layout_width="wrap_content"
          android:layout_height="wrap_content" />
      <TextView
             android:layout_width="fill_parent"
             android:layout_height="wrap_content"
             android:text="B and W: (R + G + B)/3" />
      <ImageView
          android:id="@+id/imageBW" 
          android:layout_width="wrap_content"
          android:layout_height="wrap_content" />
     </LinearLayout>
 </ScrollView>
</LinearLayout>

The code listed here convert color bitmap to gray scale by calculation. It's another approach using ColorMatrixColorFilter; refer to next article: Convert bitmap from color to GrayScale using ColorMatrixColorFilter