android 使用ColorMatrix把图变成灰色

ColorMatrix类有一个内置的方法可用于改变饱和度。
ColorMatrix cm = new ColorMatrix();
cm.setSaturation(.5f);
paint.setColorFilter(new ColorMatrixColorFilter(cm));

传入一个大于1的数字将增加饱和度，而传入一个0～1之间的数字会减少饱和度。0值将产生一幅灰度图像。

所以获得灰色图像的代码如下：

public static final Bitmap grey(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;
}