In an image editor application, transforming an original image is a common task. In this Android tip, I am going to show you how to transform an image by applying color filter to it. You can create a color filter by creating an instance of ColorFilter class passing a ColorMatrix object. The ColorMatrix object is a 4x5 matrix that is represented by a one-dimensional array. It is used to transform the color+alpha components of the original image. You can come up with a color matrix as shown below:
colorMatrix=[
a,b,c,d,e,
f,g,h,i,j,
k,l,m,n,o,
p,q,r,s,t
]

Here are the color components (Rr, Gr, Br, and Ar) of the transformed image after the color matrix is applied to its original color components (R, G, B, and A):

Rr=a*R+b*G+c*B+d*A+e;
Gr=f*R+g*G+h*B+i*A+j;
Br=k*R+l*G+m*B+n*A+o;
Ar=p*R+q*G+r*B+s*A+t;

Now to have an example application on image color filter, you create a new Android project. Then add an ImageView to the activity_main.xml file to display the transformed image.

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android=" http://schemas.android.com/apk/res/android"

   android:id="@+id/llayout"

   android:layout_width="fill_parent"

   android:layout_height="fill_parent"

   android:orientation="vertical"

  >

  <ImageView

    android:id="@+id/imgview"

    android:layout_width="wrap_content"

    android:layout_height="match_parent"

    android:padding="10dp"

    />

</LinearLayout>

import java.util.HashMap;

import java.util.List;

import android.app.Activity;

import android.graphics.Bitmap;

import android.graphics.BitmapFactory;

import android.graphics.Canvas;

import android.graphics.ColorFilter;

import android.graphics.ColorMatrix;

import android.graphics.ColorMatrixColorFilter;

import android.graphics.Paint;

import android.os.Bundle;

public class MainActivity extends Activity {

   protected void onCreate(Bundle savedInstanceState) {

      super.onCreate(savedInstanceState);

      setContentView(R.layout.activity_main);

      ImageView imageView = (ImageView) findViewById(R.id.imgview);

      // Get the front image

      Bitmap originalImg = BitmapFactory.decodeResource(getResources(), R.drawable.or_image);

      // Create  blank bitmap object

      Bitmap bitmap = Bitmap.createBitmap(originalImg.getWidth(), originalImg.getHeight(),

           Bitmap.Config.ARGB_8888);

      // Create Canvas object for drawing on the bitmap object

      Canvas canvas = new Canvas(bitmap);

      // Create paint object

      final Paint paint = new Paint();

      // Create color matrix object

      ColorMatrix colorMatrix=

           new ColorMatrix(new float[]{

                1, 0, 0, 1, 253,

                0, 0, 0, 1, 253,

                1, 0, 0, 1, 253,

                0, 0, 0, 1, 253});


      ColorFilter colorFilter= new ColorMatrixColorFilter(colorMatrix);

      paint.setColorFilter(colorFilter);

      // Apply color filtering to the original image

      canvas.drawBitmap(originalImg, 0, 0, paint);

      // Display the result image

      imageView.setImageBitmap(bitmap);

}

Posted by: Dara | post date: 03-18-2015 | Subject: Android Apps Development