1. An image processing apparatus comprising: a text area extractor that extracts multiple text areas from image data including texts; a font size calculator that calculates the font sizes of characters in each text area, the each text area being extracted by the text area extractor portion; a complexity calculator that calculates the complexities of characters in each text area, the each text area being extracted by the text area extractor portion; a necessary resolution calculator that calculates a necessary resolution for the each text area with reference to the font sizes calculated by the font size calculator and the complexities calculated by the complexity calculator; a resolution determination portion that merges text areas into a layer if a difference in the necessary resolution between the text areas is equal to or less than a specified value, the necessary resolution being calculated by the necessary resolution calculator, and that determines a necessary resolution for the layer with reference to the necessary resolutions for the text areas constituting the layer; and a resolution adjustment portion that adjusts the necessary resolutions for the text areas constituting the layer to a value identical to the necessary resolution for the layer, the necessary resolution being determined by the resolution determination portion.