table 239 which stores the mapping relationships between the color index data and the rgb values of the corresponding vbi image data therefore the converting unit 237 can look up the color table 239 according to the received color index data and then convert the color index data back into the original vbi image data decoded by the vbi data decoding 212 on the other hand the data dispatcher 231 transmits the image data of the fields to the image processing unit 232 the image processing unit 232 can perform following image process on the image data of the fields for example the image de interlacing unit 235 can de interlace the image data of the fields to generate progressive image data moreover the scaling unit 236 can perform a scaling operation on the image data of the field to generate needed image data at last image mixing unit 234 mixes the vbi image data with the de interfaced image data to generate the image to be displayed and the mixed image is sent to a display not shown to be displayed as mentioned previously because the image mixing unit 234 mixes the processed image data with the vbi image data the vbi image data is not incorrectly processed e g processed through an incorrectly de interlacing operation such that the vbi image quality can be improved in addition because the vbi image data is transmitted as the color index data.