Convert a Bitmap to GrayScale in Android

Question

Hello, I am new to this site, and I come with a question about Android.

Is there any way to convert a Bitmap to grayscale? I know how to draw a grayscale bitmap (using canvas operations: http://www.mail-archive.com/[email protected]/msg38890.html) but I really need The actual bitmap in gray colors (or at least something that could be converted to a bitmap later on). Do I have to implement it by hand (pixel by pixel operations)?

I've searched a lot, and still could not find. Anyone knows a easy/efficient way to do it?

Thanks a lot!

Answer 1

Isn't that exactly what the code you're linking to does? It takes a color bitmap ("bmp"), creates a duplicate bitmap ("bm"), and then draws the color bitmap into "bm" using the filter to turn it into grayscale. From that point on, you can use "bm" as an actual grayscale bitmap and do whatever you want to do with it.

You'd need to tweak the sample a bit (it's using hard-coded sizes, you may want to just clone the size of the original bitmap), but other than that, this seems to be as ready-to-use as it gets, depending on what you want.

Answer 2

OH, yes, it does. I was using it wrong, thanks for pointing it out to me. (Sorry for the useless question) Here is the end code (heavily based on the one linked) since it may help someone:

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;
}

Any remarks or comments on it are very welcome.

Thanks