Make sure that before using new Bitmap Image, Recycle the existing Bitmap.
and use setImageDrawable( null );
Try like this,
ImageView mImage;// YOUR IMAGEVIEW
Drawable toRecycle = mImage.getDrawable();
if ( toRecycle != null && toRecycle instanceof BitmapDrawable ) {
if ( ( (BitmapDrawable) mImage.getDrawable() ).getBitmap() != null )
( (BitmapDrawable) mImage.getDrawable() ).getBitmap().recycle();
}
mImage.setImageDrawable( null );