All pieces including pawns are taken into account. The midgame adjustment is proportional to the sum of the midgame values of all the opponent's pieces divided by the number of pieces. The endgame adjustment is proportional to the sum of the endgame values of the opponent's pieces divided by the number of pieces. So the Joker winds up being worth about one pawn more than the average piece value.
All pieces including pawns are taken into account. The midgame adjustment is proportional to the sum of the midgame values of all the opponent's pieces divided by the number of pieces. The endgame adjustment is proportional to the sum of the endgame values of the opponent's pieces divided by the number of pieces. So the Joker winds up being worth about one pawn more than the average piece value.