1. An image data transmitting apparatus comprising: a calculation device for calculating frequency of appearance of the colors of pixels constituting an image represented by image data to be transmitted to an electronic device; a deletion device for deleting, from a color palette table that includes a plurality of color palettes specifying colors of pixels constituting an image represented by image data, a color palette that corresponds to the color of a pixel whose frequency of appearance calculated by said calculation device is less than a threshold value; and a transmitting device for transmitting the color palette table, from which the color palette has been deleted, and the corresponding image data to the electronic device in a form associated with each other.