JPH059992B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a color video camera using a solid-state imaging device of a line-sequential imaging method.

[Background technology]

A color video camera that uses a solid-state image sensor (CCD), which has no afterimages or burn-in, in place of the conventional image pickup tube, has been proposed, and various improvements are being made to obtain more natural color reproduction and higher image quality. For this type of CCD color television camera, the color separation method is the key to obtaining the required resolution, and various methods such as the phase separation method, frequency separation method, and step energy method, which are considered to be highly practical, are also available. The current situation is that each has its advantages and disadvantages. for example,
When the frequency separation method is combined with the frame accumulation mode, there are problems such as equivalent afterimages caused by interlacing and flicker near the vertical limit resolution, so negative effects on image quality are unavoidable, and the field accumulation mode is used. In this case, there was a problem in that the vertical resolution was inferior to the frame accumulation mode because vertical correlation was not used.

In particular, when using a line-sequential imaging type solid-state image sensor in field accumulation mode, the signal charges of two pixels in the vertical direction are mixed, which limits the flexibility of the color multiplexing method. mode and two-line simultaneous readout color filter, it is not possible to obtain the color signals necessary for color reproduction. Therefore, when performing single-chip colorization using field accumulation mode, two pixels in the vertical direction cannot be obtained. Even if the signal charges are mixed, the luminance signals are equal in each field and each line, and
A problem arises in that a color filter configuration that can obtain at least two types of color signals on a horizontal line is required.

In an attempt to address this issue, for example, an article entitled "Single-panel color conversion method for field accumulation mode CCD" published in the Journal of the Television Society of Japan, Vol. 1.37, No. 10 (1983), used a color filter for two-pixel mixed readout. A color video camera is introduced. FIGS. 1A and 1B are a schematic circuit diagram showing an example of this type of conventional color video camera and a diagram showing an arrangement pattern of color filters of the conventional color video camera, respectively.

Conventional color video camera 1 shown in Figure 1A
uses a 2-pixel mixed readout color filter 2 in combination with a solid-state image pickup device 3, and this color filter 2 has a repeating array pattern of 2 columns and 4 rows, as shown in Figure B. In Figure 1 B, M represents magenta, Cy represents cyan, and Ye represents yellow, and the three primary colors of light are R (red), G (green), and B.
In relation to (blue), M=R+B, Cy=G+
B, Ye=G+R. The arrangement pattern of color filter 2 is that if the first line is a repeat of M, G, M, G..., the second line is a repeat of Cy, Ye, Cy, Ye..., and the third line is a repeat of M, G, M, G... It is the opposite of the first line, repeating G, M, G, M..., and the fourth line is 2
As in the row, Cy, Ye, Cy, Ye, etc. are repeated.

Here, n line in A field, n+
The luminance signal of one line is Y _Ao , Y _Ao+1 , and the color signal is
C _Ao , C _Ao+1 , luminance signals of n line and n+1 line in B field adjacent to A field.
If Y _Bo , Y _Bo+1 and color signals are C _Bo , C _Bo+1 , signal output S _o of n line and signal output S _{o +1} of n+1 line
are respectively expressed as S _o =Y _o +C _o sin ωct S _o+1 =Y _o+1 +C _o+1 sin(ωct+π). However, ωc is the solid-state image sensor 3
This is the carrier wave angular frequency of the color signal determined by the readout cycle of the color signal.

Note that each luminance signal component Y _o , Y _o+1 and each color signal component C _o , C _o+1 are as follows: Y _o ≡ (Y _e + M _g ) + (C _y + G) = 2R + 3 G + 2 B Y _{o +1} ≡ (Y _e + M _g ) + (C _y + G) = 2R + 3G + 2B _Co ≡ (Y _e + M _g ) - (C _y + G) 2R - G _{Co +1} ≡ (C _y + M _g ) - (Y _e + G) 2B - G Therefore, the luminance signal components Y _o and Y _o+1 take equal values between each field and each line.
In addition, two types of color signals C _o sin are generated from two horizontal lines.
Since ωct and C _o +1 sin(ωct+π) are obtained,
Color standard signals can be synthesized.

Therefore, the signal outputs S _o and S _o+1 are the color signal components
Since C _o and C _o+1 are modulated at the angular frequency ωc (3.58MHz), after performing band wave processing with a center frequency of ωc and a bandwidth of 1MHz, the angular frequency ωc is synchronized. If the detection is performed, the color difference signal 2R-G,
It turns out that 2B-G can be obtained. The color difference signals 2R-G and 2B-G thus obtained are modulated with color subcarriers whose phases correspond to 2R-G and 2B-G on the color coordinate axis, thereby obtaining the color signals necessary for colorization. It will be done. Below, the video processing process according to the outlined colorization method is shown in Figure 1A.
A brief explanation will be given below.

First, light from a subject passes through a lens 4, an infrared cut filter 5, a color filter 2, etc., and then forms an image on a solid-state image sensor 3. The solid-state image sensor 3 is driven by a drive circuit 3a connected to a synchronization signal generation circuit 6 using a crystal oscillation element. Among the outputs of the solid-state image sensor 3, the broadband luminance signal Y (=2R+
3G+2B) is passed through the low frequency circuit 7,
Further, the color difference signals C (=2R-G, 2B-G) are separated and extracted by passing through a band wave circuit 8 and a synchronous detection circuit 9.

After passing through the white balance circuit 10 for color temperature correction, the color difference signal C is switched to a 1H delay circuit 11a that delays the signal by one horizontal scanning period and a parallel connection circuit of signal lines, and the switching period is one horizontal scanning period.
Two types of color difference signals 2R-G, 2B- are generated by the synchronization circuit 11 to which the 1H switching circuit 11b is connected.
It becomes G. These color difference signals 2R-G, 2B-G
are balanced-modulated with predetermined color subcarriers in modulation circuits 12 and 13, added in an adder 14, and then supplied to an adder 16 for color/luminance mixing via a chroma/gamma correction circuit 15. The color/luminance mixing adder 16 is supplied with the broadband luminance signal separated and extracted by the low frequency circuit 7 via the correction circuit 17, and therefore, by adding the composite synchronization signal, An NTSC color television signal is obtained from the receiver 16.

Note that the white balance circuit 10 is supplied with a narrowband luminance signal for white balance that has passed through a low-frequency circuit 18 and a correction circuit 19 for blanking processing, which are separate from the wideband luminance signal.

By the way, the above conventional color video camera 1
is the final stage of the color signal processing system, that is, the modulation circuit 1
A chroma-gamma correction circuit 15 is connected to the next stage of the adder 14 that mixes the outputs of the two outputs. This chroma-gamma correction circuit 15 is a circuit that corrects the output signal so that it is proportional to the 1/2 to 1/3 power of the input signal in order to electrically linearize the light emission characteristics of the color picture tube. Color difference signal 2R−
Although G and 2B-G each have slightly different amounts of correction, they are added together in the adder 14 and then uniformly corrected, which has the disadvantage that appropriate chroma-gamma correction is difficult. For this reason, the conventional color video camera 1 has had drawbacks such as excessive outline emphasis in bright scenes and resolution reduction in dark scenes.

[Disclosure of the invention]

The present invention eliminates the above-mentioned drawbacks, and changes the gain of the color signal processing circuit line-sequentially according to the level of the luminance signal component included in the output of the image sensor of the line-sequential imaging method, so that the subject is bright. As the subject gets darker, the gain is increased, and the gain is increased as the subject gets darker. Also, chroma and gamma correction is performed according to the color signal without separating the color signals and without providing separate correction circuits for red and blue signals. An object of the present invention is to provide a color video camera that enables accurate chroma-gamma correction in a color signal processing circuit by switching the gain according to the color signal.

In order to achieve this object, the present invention provides a line-sequential imaging type solid-state image sensor, a wave circuit that separates color signals from the output of the solid-state image sensor, and a line-sequential line-sequential detection and modulation of the output of the wave circuit. , a color signal processing circuit that forms a color difference signal, an amplifier circuit that is included in the previous stage of the color signal processing circuit and can vary the gain to an appropriate signal level in the signal processing stage, and an amplifier circuit that is included in the output of the solid-state image sensor. a chroma-gamma correction control circuit that detects the level of a luminance signal component, varies the gain of the color signal processing circuit line-sequentially according to the detected level, and performs chroma-gamma correction; and a chroma-gamma correction control circuit that performs chroma-gamma correction according to the color signal. The gist of the present invention is to provide a switching means for switching the gain of the amplifier circuit in accordance with the color signal in order to perform this operation. In particular, the switching means includes a plurality of variable resistors and a selection switch that sequentially selects the variable resistors in one horizontal scanning period and connects them to the amplifier circuit.

According to the present invention, the gain of the color signal processing circuit is varied line-sequentially according to the level of the luminance signal component included in the output of the solid-state image sensor of the line-sequential imaging method,
In addition, since the configuration is configured to perform chroma-gamma correction by switching the gain according to the color signal component, it is possible to perform chroma-gamma correction on the line-sequential output of the solid-state image sensor for each corresponding color difference signal. It is possible to perform more accurate chroma and gamma correction than when performing chroma and gamma correction using the chroma signal processing circuit. By varying the gain of the amplifier circuit included in the front stage of the NTSC, the dynamic range of the color signal processing circuit itself is ensured, and signal transmission distortion within the color signal processing circuit is suppressed.
This has excellent effects such as being able to effectively prevent the occurrence of false colors in the process of calculating color signals in compliance with the system. In addition, as a conventional technology,
49-18424, the problem is that ``in gamma correction according to color signals, the color signals are separated into red signals and blue signals, respectively.
Since a correction circuit is provided for each, the number of circuits increases and signal calculation errors occur more often.
However, in the present invention, color signal processing is performed so that chroma/gamma correction can be applied according to the color signal without separating the color signals and without providing correction circuits for red signals and blue signals. A switching means is provided for switching the gain of the amplifier circuit included in the front stage of the circuit according to the color signal. This reduces the number of circuits and reduces signal calculation errors.

[Best mode for carrying out the invention]

Hereinafter, embodiments of the present invention will be described with reference to FIG. 2 and subsequent figures. FIG. 2 is a schematic circuit diagram showing an embodiment of the color video camera of the present invention, FIG. 3 is a diagram showing control characteristics of the chroma-gamma correction control circuit shown in FIG. 2, and FIG. FIG. 3 is a diagram showing an arrangement pattern of a modified example of the color filter shown in FIG. 2; In FIG. 2, the same components as in FIG. 1A are given the same reference numerals.

In FIG. 2, a color video camera 21 uses a color filter 2 with the same arrangement pattern as the conventional one, but the chroma-gamma correction method in the color signal processing circuit 22 after the band wave circuit 8 is different from the conventional one. A comb filter 23 is installed next to the modulation circuits 12 and 13 for synchronizing color difference signals.
Amplifier circuits 24, 25, 26 are used everywhere.
This, together with the arrangement of the above, contributes to improving image quality.

That is, an amplifier circuit 24 is provided between the solid-state image sensor 3 and the band wave circuit 8, an amplifier circuit 25 is provided between the band wave circuit 8 and the synchronous detection circuit 9, and an amplifier circuit 25 is provided between the correction circuit 19 and the white balance circuit 10. The amplifier circuit 26 is configured to perform appropriate signal amplification at each stage of signal processing. Further, regarding the amplifier circuit 25 and the amplifier circuit 26, the color difference signals 2R-G, 2B-G
Changeover switches 25a and 26a are switched by the horizontal synchronization signal from the synchronization signal generation circuit 6 so that the gain can be varied for each horizontal scanning period in accordance with the
A pair of variable gain resistors with different resistance values
R _A , R _B and r _A , r _B are connected.

Further, the circuit configuration after the white balance circuit 10 is simplified by adopting a comb filter 23, and a band wave circuit 27 connected between the comb filter 23 and the adder 16 eliminates unnecessary signals other than color signals. is configured so that it is removed.

Here, 28 is a control circuit for chroma gamma correction, and a band wave circuit 8 is connected between the amplifier circuits 24 and 25.
It is connected by bypassing. The chroma-gamma correction control circuit 28 detects the level of the luminance signal component in the amplifier circuit 24, and adjusts the gain of the amplifier circuit 25 according to the control characteristic shown in FIG. 3 according to the level of the detected luminance signal component. It has a variable configuration. That is, when the level of the luminance signal component in the amplifier circuit 24 is high, the gain of the amplifier circuit 25 is reduced, thereby reducing the degree of coloring in bright scenes, and conversely, the level of the luminance signal component in the amplifier circuit 24 is reduced. When the level is low, the gain of the amplifier circuit 25 is increased, thereby operating to prevent points that are difficult to be colored in dark scenes.

As described above, since the chroma-gamma correction control circuit 28 is provided between the amplifier circuits 24 and 25, color reproducibility can be improved from low brightness to high brightness, and images with excellent resolution and quality can be obtained. . In particular, since the amplifier circuit 25 varies the gain line-sequentially, it is possible to perform more accurate chroma-gamma correction than the conventional method in which chroma-gamma correction is performed on the color difference signal at the final stage. In addition, the amplifier circuit 25
Because the amplification in the color signal processing circuit 22 can ensure the dynamic range of the color signal processing circuit 22, it is possible to suppress signal transmission distortion within the color signal processing circuit 22, and to ensure that false colors do not occur especially at high brightness. It can be prevented. In addition, chroma and gamma correction according to color signals is performed without separating the color signals and without providing separate correction circuits for red and blue signals. , accurate chroma-gamma correction is applied according to the color signal, signal calculation errors due to a reduction in the number of circuits are reduced, and even better correction is applied.

In the case of this embodiment, a low frequency circuit 29 for suppressing the carrier wave used for synchronous detection is connected between the synchronous detection circuit 9 and the white balance circuit 10.

In addition, in this embodiment, a gamma correction circuit 30 is provided at the next stage of the low frequency circuit 7 for a wideband luminance signal.
Furthermore, a contour correction circuit 31 is provided at the next stage of the gamma correction circuit 30, and a vertical edge correction circuit 32 operated by the output of the correction circuit 19 described above is configured to perform gamma correction. It is configured to control.

Further, in this embodiment, the color filter 2 having the arrangement pattern shown in FIG. 1B was used, but the color filter 2
Alternatively, a color filter 42 having the arrangement pattern shown in FIG. 4, for example, may be used. In Figure 4,
W ^* represents 1/2R+G+B, and Ye ^* represents G+1/2R.

As explained above, according to the color video camera 21 having the above configuration, depending on the level of the luminance signal component included in the output of the solid-state image sensor 3 of the line-sequential imaging method, The gain of the amplifier circuit 25 is varied line-sequentially, and chroma-gamma correction is performed according to the color signal without separating the color signals and without providing separate correction circuits for red and blue signals. Since the configuration is configured to perform chroma-gamma correction by switching the gain according to the color signal, the line-sequential output of the solid-state image sensor 3 can be subjected to chroma-gamma correction for each corresponding color difference signal. Compared to the case where chroma and gamma correction is performed after adding signals, more accurate chroma and gamma correction is possible, and it goes without saying that it can effectively prevent a decline in color reproducibility in dark scenes and excessive coloration in bright scenes. By varying the gain of the amplifier circuit 25 included in the preceding stage of the color signal processing circuit 22, the dynamic range of the color signal processing circuit 22 itself is ensured, and signal transmission distortion within the color signal processing circuit 22 is suppressed. It is possible to effectively prevent the occurrence of false colors in the arithmetic processing process of color signals conforming to the NTSC system. In addition, by using a switching means, chroma and gamma correction is performed according to the color signals without separating the color signals and without providing separate correction circuits for red and blue signals. The number can be reduced, signal calculation errors can be reduced, and even better chroma-gamma correction can be applied.

[Brief explanation of the drawing]

1A and 1B are a schematic circuit diagram showing an example of a conventional color video camera and a diagram showing an arrangement pattern of color filters of the conventional color video camera, respectively, and FIG. A schematic circuit configuration diagram showing one embodiment; FIG. 3 is a diagram showing control characteristics of the chroma-gamma correction control circuit shown in FIG. 2; FIG. 4 is a modified example of the color filter shown in FIG. 2. It is a figure showing an arrangement pattern of. 2, 42...Color filter, 3...Solid-state image sensor, 8
... Bandwidth circuit, 22... Color signal processing circuit, 28...
Chroma-gamma correction control circuit, 25a...switch switch, R _A , R _B ... variable resistor.

Claims (1)

[Scope of Claims] A solid-state image sensor of a one-line sequential imaging system, a separation means for separating a color signal from the output of the solid-state image sensor, and a method for detecting and modulating the output of the separation means in a line-sequential manner to generate a color difference signal. an amplifier circuit included in the preceding stage of the color signal processing circuit and capable of varying the gain to an appropriate signal level in the signal processing stage; and a luminance signal component included in the output of the solid-state image sensor a chroma-gamma correction control circuit for detecting a level and varying the gain of the amplifier circuit according to the detected level to perform chroma-gamma correction; and a gain of the amplifier circuit for performing chroma-gamma correction according to the color signal. A color video camera comprising: a switching means for selectively switching sequentially corresponding to one horizontal scanning period. 2. The switching means includes: a plurality of variable resistors; and sequentially selecting the variable resistors in one horizontal scanning period;
2. A color video camera according to claim 1, further comprising a selection switch connected to said amplifier circuit.