A recent increase in audio-visual oriented applications has led to a desire for the development of a TV receiver that can obtain higher resolution images. In order to satisfy the desire in turn, a Hi-vision TV receiver has been developed. The Hi-vision TV receiver uses 1125 scanning lines, which are at least twice the number of the scanning lines used in an NTSC-system receiver of 525. Also, the Hi-vision receiver has an aspect ratio of 9:16 as compared to the NTSC-system receiver's aspect ratio of 3:4. As such, the Hi-vision receiver can display an image with a higher resolution and realism than the NTSC-system one.
Although the Hi-vision system has these excellent features, the Hi-vision receiver cannot display a Hi-vision image when an NTSC-system video signal is supplied as it is. The reason is that, as mentioned above, the NTSC system and the Hi-vision system have different standards.
To display the Hi-vision image corresponding to the NTSC-system video signal, the applicant of this application previously disclosed a converter for converting the NTSC-system video signal into the Hi-vision video signal (see Japanese Patent Application No. Hei 6-205934). This converter extracts, from an NTSC-system video signal, pixel data sets of a block (region) of the NTSC-system video signal, which correspond to an objective position in a Hi-vision video signal, thereby deciding a class including the pixel data set of the objective position based on level distribution patterns of the pixel data sets in this block and then producing the pixel data set of the objective position corresponding to this class.
In the above-mentioned converter, a memory beforehand stores the coefficient data sets to be used in the estimation equation of each class so that as more classes are to be grouped, the number of the required coefficient data sets to be used in the estimation equation also increases, thus requiring a mass-capacity of the memory.
Also, in the above-mentioned converter, an image according to the Hi-vision video signal has a fixed resolution and so cannot have a desired resolution corresponding to the image contents, unlike the conventional adjustment of contrast, sharpness, etc. To obtain a desired picture quality, therefore, a memory may beforehand store the coefficient data sets to be used in the estimation equation of every picture quality. This, however, leads to an increase in the amount of the required coefficient data sets to be used in the estimation equation, thus requiring a mass-capacity memory.