图片变灰色处理

/**
* 图片变灰处理（多次处理,色彩会反复）
*
* @param bitmap
* @return
*/
public static final Bitmap createBitmap(Bitmap bitmap) {
    int width = bitmap.getWidth();
    int height = bitmap.getHeight();

    Bitmap faceIconGreyBitmap = Bitmap
            .createBitmap(width, height, Bitmap.Config.ARGB_8888);

    Canvas canvas = new Canvas(faceIconGreyBitmap);
    Paint paint = new Paint();
    ColorMatrix colorMatrix = new ColorMatrix();
    colorMatrix.setSaturation(0);
    ColorMatrixColorFilter colorMatrixFilter = new ColorMatrixColorFilter(
            colorMatrix);
    paint.setColorFilter(colorMatrixFilter);
    canvas.drawBitmap(bitmap, 0, 0, paint);
    return faceIconGreyBitmap;
}