Android : Converting color image to grayscale

Question

I am trying to convert color image into grayscale using the average of red, green, blue. But it comes out with errors.

Here is my code

imgWidth = myBitmap.getWidth();
imgHeight = myBitmap.getHeight();
                    
for(int i =0;i<imgWidth;i++) {
    for(int j=0;j<imgHeight;j++) {
     int s = myBitmap.getPixel(i, j)/3;
     myBitmap.setPixel(i, j, s);
    }
}
                    
ImageView img = (ImageView)findViewById(R.id.image1);
img.setImageBitmap(myBitmap);

But when I run my application on Emulator, it's force close. Any idea?

I have solved my problem use the following code:

for(int x = 0; x < width; ++x) {
            for(int y = 0; y < height; ++y) {
                // get one pixel color
                pixel = src.getPixel(x, y);
                // retrieve color of all channels
                A = Color.alpha(pixel);
                R = Color.red(pixel);
                G = Color.green(pixel);
                B = Color.blue(pixel);
                // take conversion up to one single value
                R = G = B = (int)(0.299 * R + 0.587 * G + 0.114 * B);
                // set new pixel color to output bitmap
                bmOut.setPixel(x, y, Color.argb(A, R, G, B));
            }
        }

Are you getting any exact error in log? such as stackoverflow? — TeaCupApp, Dec 05 '11 at 05:59

score 90 · Answer 1 · edited Jul 22 '19 at 07:11

90

You can do this too :

    ColorMatrix matrix = new ColorMatrix();
    matrix.setSaturation(0); 
    imageview.setColorFilter(new ColorMatrixColorFilter(matrix));

edited Jul 22 '19 at 07:11

Sachin

3,815
2
13
26

answered Dec 29 '12 at 17:55

E Player Plus

1,676
15
19

Is it possible to make it only full-black (0xff000000) and full-white (0xffffffff) ? – android developer May 25 '15 at 10:17
@androiddeveloper You can do that with ImageView's built-in setColorFilter(color, mode) method or a regular PorterDuffColorFilter. http://developer.android.com/reference/android/graphics/PorterDuffColorFilter.html – Pkmmte Nov 13 '15 at 02:42
@Pkmmte What's the regular PorterDuffColorFilter ? – android developer Nov 13 '15 at 08:08
This is not working for me. I am setting the image in imageview using imageView.setImageBitmap(). – binaryKarmic Jan 19 '16 at 14:57
1

This method is more reliable than converting the image to Bitmap. – capt.swag Sep 26 '16 at 08:32

score 32 · Answer 2 · edited May 23 '17 at 12:26

32

Try the solution from this previous answer by leparlon:

public Bitmap toGrayscale(Bitmap bmpOriginal)
    {        
        int width, height;
        height = bmpOriginal.getHeight();
        width = bmpOriginal.getWidth();    

        Bitmap bmpGrayscale = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565);
        Canvas c = new Canvas(bmpGrayscale);
        Paint paint = new Paint();
        ColorMatrix cm = new ColorMatrix();
        cm.setSaturation(0);
        ColorMatrixColorFilter f = new ColorMatrixColorFilter(cm);
        paint.setColorFilter(f);
        c.drawBitmap(bmpOriginal, 0, 0, paint);
        return bmpGrayscale;
    }

edited May 23 '17 at 12:26

Community

1
1

answered Dec 05 '11 at 06:09

Lalit Poptani

65,659
21
155
238

1

How can I also lighten the image? The image is now gray, but it is also dark because of the colors in the original image. – Andrew Sep 10 '13 at 16:09
so after converting it to black and white will image size reduced ? (size in kb) – Kalpesh Lakhani Jun 21 '14 at 07:16
Lalit can u tell me how can we extract character from grayscale image? – Faisal Ashraf Feb 02 '15 at 13:50
Me want dat codez and u answer my question plz! – 700 Software Feb 12 '16 at 22:37
2

Seriously folks, it's usually best to make a new question instead of commenting on an old thread. – 700 Software Feb 12 '16 at 22:38
I am trying this in the Android 10 but i get an exception "Software rendering doesn't support hardware bitmaps". Why is that? – james04 Mar 31 '20 at 14:02

score 14 · Answer 3 · answered Dec 05 '11 at 09:19

Lalit has the most practical answer. However, you wanted the resulting grey to be the average of the red, green and blue and should set up your matrix like so:

    float oneThird = 1/3f;
    float[] mat = new float[]{
            oneThird, oneThird, oneThird, 0, 0, 
            oneThird, oneThird, oneThird, 0, 0, 
            oneThird, oneThird, oneThird, 0, 0, 
            0, 0, 0, 1, 0,};
    ColorMatrixColorFilter filter = new ColorMatrixColorFilter(mat);
    paint.setColorFilter(filter);
    c.drawBitmap(original, 0, 0, paint);

And finally, as I have faced the problem of converting an image to grayscale before - the most visually pleasing result in all cases is achieved by not taking the average, but through giving each colour different weight depending on its percieved brightness, I tend to use these values:

    float[] mat = new float[]{
            0.3f, 0.59f, 0.11f, 0, 0, 
            0.3f, 0.59f, 0.11f, 0, 0, 
            0.3f, 0.59f, 0.11f, 0, 0, 
            0, 0, 0, 1, 0,};

@user1324936 care to elaborate? – Jave Apr 26 '14 at 08:25 — Jave, Apr 26 '14 at 08:25

Android : Converting color image to grayscale

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