Conventionally, in color solid-state image pickup devices of the three-plate type, three solidstate image pickup devices for green, red and blue are used and their sensitivity characteristics are matched; therefore, even if radiation sensitive devices were saturated, no problem is caused in producing a white image.
On the contrary, in color solid-state image pickup devices of the single-plate type, the sensitivity on the side of a short wavelength (blue sensitivity) of the solid-state image pickup device is generally low and this causes the picture quality to deteriorate; therefore, a method is adopted whereby a cyan (blue green) filter is used in place of a blue filter, thereby improving the resolution. However, due to a difference in transmission factor of each color filter, the quantities of incident light which saturate the radiation sensitive devices differ from one device to another, so that this causes a problem such that a false color signal is generated in photographing an object with high brightness. For example, in the case where the transmission factor of each color filter in such a color filter array as shown in FIG. 1 is as shown in FIG. 2, the saturation state of each radiation sensitive device to the quantity of incident light is such that the radiation sensitive device corresponding to the Cy (cyan) filter would have been saturated with less quantity of radiation than in the case of the radiation sensitive devices corresponding to R (red) and G (green) filters, as shown in FIG. 3. In this case, since the B (blue) signal is obtained by subtracting the G signal from the Cy signal, when the radiation sensitive device responsive to Cy is saturated, the B signal starts decreasing and when the radiation sensitive devices responsive to both Cy and G are saturated, the B signal will disappear. This results in a yellow false color signal, causing the reproduced image to be unnatural.
In consideration of such a problem, a method has been proposed whereby as shown in FIG. 5, the transmission characteristic of the color filter is selected as shown in FIG. 4 in the manner such that the quantities of saturation light of the radiation sensitive devices corresponding to each of the R, G and Cy color filters are identical. However, even this example also has a drawback such that the quantity of saturation light of each radiation sensitive device changes with a change in color temperature, so that correct saturation light quantities cannot be obtained. Although the execution of color temperature correction or compensation for every color filter enables the occurrence of such a problem as mentioned above to be eliminated, an apparatua to realize this purpose will be complicated and expensive. To solve such a drawback, a method can be considered whereby the saturation output signal level is detected and a color carrier signal (color signal-modulated carrier signal) is suppressed by this detection signal. However, in a system with a recording apparatus built-in instead of a general video system, there may be a case where a luminance signal and a color signal are directly put in a magnetic recording circuit without passing through an NTSC encoder. In such a system, it is impossible to use the above-mentioned means for suppressing the color carrier signal by way of the saturation level detection signal as it is. In addition, if one intends to, for example, restrict the level or to cut the color subcarrier at the stage of such a color carrier signal, there is a drawback such that a range of the color signal to be suppressed will have been widened in the direction of the time base due to the function of a low-pass filter which is ordinarily included in the separation process of each color signal, and that a positional difference will be caused between the position where the brightness level exceeds a reference level and the position of the color signal to be suppressed. This results in a cause of an error signal.
Particularly, such a problem is critical in a wide-band image pickup system.
Now considering the case of performing such suppression of color signal in the color separation circuit for color separating an output of the image sensor, amplifiers and the like for suppression must be equipped for every color. This causes drawbacks such that the system configuration becomes complicated and it is difficult to easily balance the performance and characteristics of those amplifiers.