I had been through the same issue. Before you set the downloaded bitmap to your ImageView, you have to compress your bitmap according to the width and height of your ImageView. 
You have to create a scaled bitmap like this,
 bm1=Bitmap.createScaledBitmap(bm, 300, 300,true);
imgView.setImageBitmap(bm1);
or Compress your bitmap like this,
            OutputStream fOut = null;
                        File file = new File(strDirectoy,imgname);
                            fOut = new FileOutputStream(file);
                        bm1.compress(Bitmap.CompressFormat.JPEG, 85, fOut);
                            fOut.flush();
                            fOut.close();
                MediaStore.Images.Media.insertImage(getContentResolver(),file.getAbsolutePath(),file.getName(),file.getName());