读取sd卡下图片，由图片路径转换为bitmap

01 public Bitmap convertToBitmap(String path, int w, int h) {
02 BitmapFactory.Options opts = new BitmapFactory.Options();
03 // 设置为ture只获取图片大小
04 opts.inJustDecodeBounds = true;
05 opts.inPreferredConfig = Bitmap.Config.ARGB_8888;
06 // 返回为空
07 BitmapFactory.decodeFile(path, opts);
08 int width = opts.outWidth;
09 int height = opts.outHeight;
10 float scaleWidth = 0.f, scaleHeight = 0.f;
11 if (width > w || height > h) {
12 // 缩放
13 scaleWidth = ((float) width) / w;
14 scaleHeight = ((float) height) / h;
15 }
16 opts.inJustDecodeBounds = false;
17 float scale = Math.max(scaleWidth, scaleHeight);
18 opts.inSampleSize = (int)scale;
19 WeakReference<Bitmap> weak = new WeakReference<Bitmap>(BitmapFactory.decodeFile(path, opts));
20 return Bitmap.createScaledBitmap(weak.get(), w, h, true);
21 }

其中w和h你需要转换的大小

path转换为bitmap:上面方法即可；
imageview获取drawable并转换为 bitmap ：Bitmap bt= ((BitmapDrawable) mImageview.getDrawable()).getBitmap();
resourceid转换为bitmap：Bitmap bt = BitmapFactory.decodeResource(getResources(), R.drawable.resourceid);
Drawable转换为bitmap：Bitmap bt= ((BitmapDrawable) Drawable).getBitmap();
因为BitmapDrawable是继承Drawable，所以可以灵活的转换