JPH0137077B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a color solid-state imaging device. [Background of the Invention] In a solid-state image sensor, for example, a MOS image sensor consisting of a photodiode array and an X-Y address MOS transistor switch, picture elements in a specific positional relationship are internally connected to each other as shown in Figure 1. , can be easily read out to separate output lines. In the apparatus shown in FIG. 1, for example, color filters shown in FIG. 2 are arranged corresponding to the picture elements of the image sensor. Here, W is a filter corresponding to a luminance signal, and has the property of passing light components of all colors. In reality, it only needs to be transparent, and can be expressed as W=R+G+B.
Cy is cyan (G+B), Ye is yellow (G+R)
means. When configuring a color camera, it is sufficient to obtain three signals containing the three primary colors R, G, and B in different proportions, and it is clear that there are many combinations of filters, not just the one example above. . The gist of the present invention will be explained below by taking as an example a case in which the image sensor shown in FIG. 1 and the color filter shown in FIG. 2 are combined. The image sensor shown in FIG. 1 includes a horizontal shift register 11 for horizontal scanning, a vertical shift register 12 for vertical scanning, a horizontal readout switch 13,
It consists of a photodiode 14 forming each pixel, a vertical readout switch 15, and a switch 16 for interlacing horizontal lines. In this image sensor, two horizontal lines n, n+
1 are simultaneously scanned, and signals of pixels located in the same positional relationship are collectively extracted on the same signal line, using 4 pixels each consisting of 2 pixels horizontally and vertically as a unit. In the device shown in FIG. 1, the upper left and lower right elements (W in FIG. 2) of each of the four pixels are connected to the same output line 17,
The other two are connected to separate output lines 18,19. According to this image sensor, interlacing can be performed by switching the combination of two horizontal lines to be simultaneously scanned for each field using the switch 16. When the filter shown in Fig. 2 is arranged, W is from output line 17 to Cy
can be taken out independently from the output line 18, and Ye can be taken out from the output line 19, respectively. The output from an image pickup device 31 in which the filter shown in FIG. 2 is arranged in the element shown in FIG. 1 is conventionally processed by, for example, a signal processing circuit shown in FIG. 3. That is, each signal output from the image sensor 31 passes through a preamplifier group 32, and then passes through low-frequency amplifiers 33, 34, 35 to arithmetic circuits 36, 3.
7 and 38, and the R and B signals are separated by performing the following calculation. R=W-Cy...(1) B=W-Ye...(2) Y=W+Cy+Ye...(3) The W, R, and B signals obtained in this way are converted to NTSC through process circuits 39, 40, and 41. The signal is sent to an encoder 42 and becomes a composite signal. It is known that a narrow band (500KHz) is usually sufficient for the color signals R and B. However, considering the frequency spectrum of the Cy output and Ye output of the image sensor 31, as shown in Fig. 4,
Baseband components 43 of Cy and Ye, and carrier component 44 in which the Cy and Ye signals are modulated at the readout period
The signal processing shown in FIG. 3 uses only the baseband component and does not use the carrier component. [Object of the Invention] The object of the present invention is to configure a color signal using both the baseband component and carrier component signals,
The purpose is to improve the signal-to-noise ratio of color signals. [Embodiment of the Invention] FIG. 5 shows an embodiment of the present invention in which the apparatus of FIG. 3 is used. The output signals Cy and Ye are respectively guided to low frequency wave generators 34 and 35 for obtaining baseband components and band wave wave generators 51 and 52 for obtaining carriers.
As mentioned above, the carrier component is the carrier frequency fc
A band of ±500KHz is sufficient. This carrier component is obtained in the form of an AM modulated signal, so a detector (envelope detection or synchronous detection)
Cy and Ye signals are obtained by 53 and 54. These signals are obtained from the low frequency filters 34 and 35.
Adders 55 and 56 add to the Cy and Ye signals, respectively. Generally, when two signals with the same signal-to-noise ratio (S/N) and correlation are added, the signal-to-noise ratio improves by 3 dB. If the S/Ns of the two are different, there is a mixing ratio that provides the best S/N. This will be discussed below. Let the noise when the two signal amplitudes are normalized to 1 be a and b, respectively (that is, the S/N is 20log1/a and 20log1/b). Two signals k:
When adding 1, the signal amplitude after addition becomes k+1, and the noise amplitude becomes √() ² + ² . Therefore, the S/N is Solving the above equation for K, when k = (b/a) ² , S/
It can be seen that N takes the maximum value. S/N at this time
Assuming that the degree of improvement is a<b, becomes. In other words, if the signals are mixed at a ratio of (b/a) ² :1, the S/N after addition is

〔Effect of the invention〕

By using the present invention, the S/N of a solid-state camera can be improved.
The effect is significant because the ratio can be improved and good image quality can be obtained even under low-light imaging conditions. It is clear that the present invention is applicable not only to the above-mentioned MOS type solid-state camera but also to cameras using other imaging devices.

[Brief explanation of drawings]

FIG. 1 shows one of the solid-state image sensors applied to the present invention.
FIG. 2 is a diagram showing an example of a color filter used with the solid-state image sensor, FIG. 3 is a block diagram of a conventional signal processing circuit that processes the output signal from the solid-state image sensor, and FIG. FIG. 4 is a diagram showing the frequency spectrum of the output signal of the solid-state image sensor, FIG. 5 is a circuit diagram showing an example of the signal processing circuit according to the present invention, and FIG. 6 is a diagram showing the frequency characteristics of the noise contained in the signal. Explanatory drawings, FIGS. 7 and 8 are filter arrangement diagrams and signal explanatory diagrams in other embodiments of the present invention, and FIGS. 9 and 10 are filter arrangement diagrams and signal processing in still other embodiments of the present invention. The circuit configuration diagram, FIG. 11, is a signal explanatory diagram of the above embodiment circuit. In FIG. 5, 31 is a solid-state image sensor, 33,
Reference numerals 34 and 35 indicate low-frequency wave generators, 51 and 52 band wave generators, and 53 and 54 wave detectors.

Claims (1)

[Claims] 1. A color filter consisting of a plurality of types of regularly arranged filter elements, a photoelectric conversion element that picks up an image through the color filter and outputs a video signal according to input light, and an output signal of the photoelectric conversion element. a preamplifier for amplification; a percival coil that is provided before the preamplifier and has a resonant frequency equal to the frequency of the carrier portion of the output signal of the photoelectric conversion element;
a low-pass filter for separating and extracting a baseband signal and a carrier signal for each color component corresponding to each filter from the output signal of the preamplifier;
and a bandpass filter, and a signal processing circuit that generates an NTSC color composite signal from a luminance signal and a color signal obtained by adding the outputs of both the filters.