android把彩色图像变成灰度图（黑白）

ImageView iv = new ImageView(this);
setContentView(iv);
Bitmap originImg = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher);
Bitmap grayImg = Bitmap.createBitmap(originImg.getWidth(), originImg.getHeight(), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(grayImg);
Paint paint = new Paint();
ColorMatrix colorMatrix = new ColorMatrix();
colorMatrix.setSaturation(0);
ColorMatrixColorFilter colorMatrixFilter = new ColorMatrixColorFilter(colorMatrix);
paint.setColorFilter(colorMatrixFilter);
canvas.drawBitmap(originImg, 0, 0, paint);
iv.setImageBitmap(grayImg);

这里起关键作用的是colorMatrix.setSaturation(0);

0会把图像变成灰度图。只有黑白。