1. Field of the Invention
This invention relates to an image signal processing apparatus which processes image signals.
2. Description of the Prior Art
In a single-plate color video camera for commercial use or the like, a striped filter is mounted in front of a solid-state image pickup device whose output is subjected to sampling, and a luminance signal, a color-difference signal, and R, G and B signals are formed by performing interpolation whenever necessary. As is known, R, G and B represent red, green and blue.
For example, an output from a solid-state image pickup device which mounts a complementary-color filter comprises signals as shown in FIG. 1. If attention is paid to a signal Wr (=2R+G+B), Wr signals are obtained only at every other picture element in the horizontal direction, and at every other line (every two lines in the case of interlaced scanning) in the vertical direction, as shown in FIG. 2. For the remaining picture elements, an average value of surrounding Wr signals is adopted, for example, as shown in FIG. 3. This processing is termed simultaneous processing. Wb (=R+G+2B), Gb (=2G+B), and Gr (=R +2G) signals obtained by the above-described simultaneous processing are subjected to matrix calculation, whereby a luminance signal, a color-difference signal, and R, G and B signals are obtained.
Recently, the above-described camera signal processing has been digitized, and line memories have been used as 1H delay means for performing interline processing. The output of the image pickup device is first converted into a digital signal by an A/D (analog-to-digital) converter, and thereafter the above-described processing and other kinds of camera signal processing are performed.
While it is possible to exactly perform complicated signal processing with the digital signals, it is necessary to provide an A/D converter, signal lines for the number of bits, and the like, causing an increase in the scale of circuitry. In particular, the A/D converter consumes greater electric power than other circuits. Hence, it is difficult to mount the A/D converter in the form of a chip, and to reduce power consumption of the entire signal processing apparatus.