Abstract
Differences in three dimensional noise characteristics between the current NTSC television systems and letterbox EDTV systems are studied. We showed that when pictures are displayed in an area of the identical picture height, and signal to noise ratio of the transmission signals is maintained at the same level, as in NTSC, the three-dimensional noise power spectrum of the main panel of letterbox EDTV is transformed into the low spatial frequency area with high density, although the total noise power is unchanged. On the other hand, helper signals which are multiplexed onto the black bars, the top and bottom portions of letterbox picture, generally increase the total noise power even if the multiplexing amplitude is large enough. By applying a three-dimensional weighting function, it is shown that the weighted noise power of letterbox EDTV becomes larger than that of a conventional television system. Hence, to retain the existing NTSC service area after introducing EDTV broadcasting, it will be necessary to install noise suppressing measures in the EDTV system.
