Unity3d ScreenPointToLocalPointInRectangle

I'm having some troubles with the ScreenPointToLocalPointInRectangle() function. This is my code:

void OnTouch(Vector2 position) {
    Vector2 pos;
    if (RectTransformUtility.ScreenPointToLocalPointInRectangle (bgImage.rectTransform, position, Camera.main, out pos)) {
        pos.x = (pos.x / bgImage.rectTransform.sizeDelta.x);
        pos.y = (pos.y / bgImage.rectTransform.sizeDelta.y);
    }

It's not doing anything, the instructions inside the 'if' are not executed. I used Debug.Log() to check the position variable and it's fine.

How can I fix this?