14. The computing device of claim 12 , wherein the opacity of the control object is adjustable between transparent and opaque.
14. The computing device of claim 12 , wherein the opacity of the control object is adjustable between transparent and opaque. 16. The computing device of claim 14 , wherein controlling the perceived visible brightness of the electronic document based on the second touch input comprises: increasing the perceived visible brightness of the electronic document by decreasing the opacity of the control object.