读取sd卡下图片，由图片路径转换为bitmap

public Bitmap convertToBitmap(String path, int w, int h) {

            BitmapFactory.Options opts = new BitmapFactory.Options();

            // 设置为ture只获取图片大小

            opts.inJustDecodeBounds = true;

            opts.inPreferredConfig = Bitmap.Config.ARGB_8888;

            // 返回为空

            BitmapFactory.decodeFile(path, opts);

            int width = opts.outWidth;

            int height = opts.outHeight;

            float scaleWidth = 0.f, scaleHeight = 0.f;

            if (width > w || height > h) {

                // 缩放

                scaleWidth = ((float) width) / w;

                scaleHeight = ((float) height) / h;

            }

            opts.inJustDecodeBounds = false;

            float scale = Math.max(scaleWidth, scaleHeight);

            opts.inSampleSize = (int)scale;

            WeakReference<Bitmap> weak = new WeakReference<Bitmap>(BitmapFactory.decodeFile(path, opts));

            return Bitmap.createScaledBitmap(weak.get(), w, h, true);

        }