9. A display device, comprising: a signal input device configured to receive a signal including video data and supplementary information, the supplementary information including text data, position information of the text data relative to the video data, and size information of the text data; a display configured to display the received signal so that the text data overlap the video data according to the position information and the size information; a controller configured to detect color information of the text data, select a portion of the video data based on the position information and the size information, detect color information of the selected portion, determine a color difference between the video data and the text data included in the received signal, based on the detected color information of the text data and the detected color information of the selected portion, and compare the determined color difference with at least one reference value; and a video processor configured to control a display characteristic of the text data depending on a result of the comparing by said controller, the text data display characteristic control comprising only one of: controlling the color difference between the text data and the video data by controlling a color of the displayed text data; and controlling a luminance of the displayed text data.
12. The display device according to claim 9 , wherein the luminance of the displayed text data is controlled when the color difference is greater than or equal to the at least one reference value.