为位图图像添加透明度

Question

我已将彩色图像转换为黑白图像，如下所示。

        //convert color to black&white
        private Bitmap convertColorIntoBlackAndWhiteImage(Bitmap orginalBitmap) {
            ColorMatrix colorMatrix = new ColorMatrix();
            colorMatrix.setSaturation(0);
            ColorMatrixColorFilter colorMatrixFilter = new ColorMatrixColorFilter(
                    colorMatrix);
            Bitmap blackAndWhiteBitmap = orginalBitmap.copy(Bitmap.Config.ARGB_8888, true);
            Paint paint = new Paint();
            paint.setColorFilter(colorMatrixFilter);
            Canvas canvas = new Canvas(blackAndWhiteBitmap);
            canvas.drawBitmap(blackAndWhiteBitmap, 0, 0, paint);        

            return blackAndWhiteBitmap;
        }

如何为黑白图像添加一半透明度，大约50%的透明度？感谢

Answer 1

BitmapDrawable bd =
    new BitmapDrawable(convertColorIntoBlackAndWhiteImage(bMap));
bd.setAlpha(50);
imageView1.setImageDrawable(bd);