将bitmap修改为灰阶，减小图片大小

public static 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;}