JP2650969B2 - Digital television camera device - Google Patents

Description

The present invention relates to an image sensor, an A / D converter for converting a video signal obtained from the image sensor from analog to digital, and the A / D converter.
And a digital signal processing circuit for processing a digital video signal output from the converter. More specifically, the present invention relates to a digital television camera device comprising: The present invention relates to such a digital television camera device capable of reducing the deterioration of the S / N ratio due to a bit error.

[Conventional technology]

2. Description of the Related Art In recent years, digitalization of electronic circuits has progressed, and electronic circuits have become widespread in the field of television cameras. The advantages of the digitization of the signal system of the television camera are that large-scale integration is simplified with the rapid improvement of semiconductor manufacturing technology, the signal system can be simplified, and signal processing unique to the television camera. White balance, γ correction, and the like can be accurately and easily performed by calculation.

FIG. 2 is a block diagram showing an example of the configuration of the digital color camera. FIG. 1 is also shown in FIG. 1 of JP-A-61-280189, wherein 1 is an image sensor, 2 (2 ₁ , 2 ₂ ) is a preamplifier, and 3 (3 ₁ , 3 ₂ ) is an analog / digital A converter (A / D converter), 4 is a digital signal processing circuit, and 5 is a digital / analog converter (D / A converter).

After the analog video signal obtained from the image sensor 1 is amplified by the preamplifier 2, it is converted into a digital signal by the A / D converter 3, and the digital signal processing circuit 4 demodulates the color signal, white balance, and γ correction. Gives special signal processing,
The signal is returned to an analog signal by the D / A converter 5. In FIG. 2, the output of the image sensor 1, the preamplifier 2, and the A / D converter 3 are shown as using two systems. However, in the case of a color camera, it is necessary to use a plurality of systems. It is not necessary to stick to two systems because it has the meaning shown.

[Problems to be solved by the invention]

The above prior art does not take into account (i) nonlinear signal processing, that is, signal processing unique to a television camera, that is, γ correction (ii) white balance.

Here, the γ-correction means that the transmission / reception system of a television uses an imaging camera or a picture tube in which the relationship between input and output is not linear in various conversion processes. It is necessary to make corrections in advance, and that such corrections, white balance,
It is well known that the adjustment is performed to adjust the levels of the three-channel signals so that an achromatic (white) image is obtained from a bright portion to a dark portion.

 First, (i) γ correction will be described with reference to FIG.

2A shows the input of the A / D converter 3 with respect to the light amount (incident light amount) of the optical image formed on the image sensor 1, and FIG.
The input / output relationship of the / D converter 3 is shown, and the input / output relationship of the digital signal processing circuit 4 is shown in FIG. 3 (a) and 3 (b) that the A / D converter 3 receives a video signal proportional to the amount of incident light, and the A / D converter 3 also outputs a digital signal proportional to the input signal. Will be appreciated.

At this time, when the A / D converter 3 performs the analog-to-digital conversion, the bit errors Δ ₁ and Δ ₂ generated due to the quantization error (quantization noise) are input to the digital signal processing circuit 4 as they are. Is done.

On the other hand, since the digital signal processing circuit 4 performs γ correction as described above, its input / output characteristics are as shown in FIG. 3 (c). That is, the bit error delta ₁ which occurs when a small amount of signal is a signal processing circuit will be enlarged in the output of the 4 bit error delta ₂ which occurs when large reverse the signal amount would be reduced. Therefore, the S / N ratio when the signal amount is small deteriorates, and furthermore, the S / N ratio
There is a problem that the S / N ratio is further deteriorated when a digital signal whose ratio is deteriorated is used for calculation.

Further, as shown in FIG. 3 (d), if the input / output characteristics of the A / D converter 3 are set to the same characteristics (y = x1 ^{/ γ} ) as those of the γ correction, the gradation becomes extremely small when the input signal is small. , And generally requires an accuracy exceeding the input resolution of the A / D converter 3. That is, A /
It is necessary to adjust the resistance value of the reference resistor r for creating the quantization step at the input section of the D converter 3 very accurately.

In the figure, Vref.1 and Vref.2 are reference voltages, Iref
Is an input terminal, and 6 (6 ₁ , 6 ₂ ,..., 6 _n ) is a comparator. The analog signal input from the input terminal I becomes a digital signal and is output from the comparators 6 _{1 to} 6 _n. .

Further, when the input signal of the A / D converter 3 is a plurality of complementary color signals (for example, cyan, magenta, etc.), white balance can be obtained when the signal amounts of the plurality of complementary color signals are different. No correction can be made.

Next, (ii) white balance will be described. In television cameras, the color temperature of the illumination light is generally
It is necessary to maintain a white balance even if it changes in the range of about _000K . When the color temperature changes in the above range, the signal output levels of the imaging element 1 and the preamplifier 2 change from double to about half. Therefore, the input range of the A / D converter 3 cannot always be used effectively, and the S / N
There was a problem that the ratio deteriorated.

When the color filter used for the image sensor 1 is a primary color filter, the output signals of the image sensor 1 and the preamplifier 2 are a plurality of primary color signals. Therefore, the signal levels of the plurality of primary color signals are adjusted (white balance is obtained). After) A /
If the signal is input to the D converter 3, the input range of the A / D converter 3 can always be used effectively. However, an analog circuit for obtaining white balance is required, and the circuit scale increases. It is difficult to improve the performance as compared with white balance. When a plurality of complementary color signals are input to the A / D converter 3 using a complementary color filter, white balance cannot be obtained by adjusting the signal levels as described above.

An object of the present invention is to reduce the deterioration of the S / N ratio due to the bit error caused by the above-described signal processing peculiar to the television camera, which is caused by the white balance of (ii). It is to provide a digital television camera device capable of performing such operations.

[Means for solving the problem]

In order to achieve the above object, according to the present invention, an image sensor, a plurality of A / D converters for respectively performing analog-to-digital conversion of a plurality of video signals obtained from the image sensor, and the plurality of A / D converters And a digital signal processing circuit for performing digital processing by inputting digital video signals of a plurality of systems, which are outputs of the device, in a digital television camera apparatus, at least a plurality of video signals obtained from the image sensor. Are provided on each signal path until they are input to the corresponding A / D converters, respectively, and the level of each video signal input to each of the A / D converters via the amplifiers provided therethrough. In order to enable the effective use of the input range in each of the A / D converters, the gain switching of each of the amplifiers is made the most from a predetermined combination of amplifier gains. In the form of selecting an appropriate one, a fixed gain switching circuit to be performed, and a white level by adjusting the level of each of the video signals that have been input through the respective A / D converters and that are substantially aligned in level. The digital signal processing circuit having a means for balancing.

[Action]

The gain of each amplifier is switched so that the level of each video signal input to each of the A / D converters through each of the amplifiers is substantially aligned, and thus the white balance is coarsely adjusted even if it is not accurate. If so, the input range of the A / D converter 3 can be used effectively, and the aforementioned S / N ratio deterioration is reduced.

〔Example〕

Hereinafter, an embodiment of the present invention will be described. Before that, an example of a circuit configuration of a digital television camera device useful for understanding the embodiment of the present invention will be described with reference to FIG. In the figure, 1 is an image sensor, 2 (2 ₁ , 2 ₂ ) is a preamplifier, 5 is a D / A converter, and 7 (7 ₁ , 7 ₂ ) has a fifth input / output characteristic.
A / D converter with polygonal line characteristics as shown in the figure, 8
Denotes a digital signal processing circuit, 100 (100a, 100b) denotes a gain correction circuit, and 101 denotes an arithmetic circuit.

Components that can be shared with the conventional example of FIG. 2 are denoted by the same reference numerals. Further, although the number of output lines of the image sensor 1 and the number of preamplifiers 2 are two each, it is not necessary to be limited to this. Gain correction circuit 100 in digital signal processing circuit 8 (y = (1 / a1) x, y = (1 / a2) x, y =
An inverse coefficient of (1 / a3) x is added to return the signal to a linear signal, and the arithmetic circuit 101 performs an operation such as white balance, and then performs γ correction.

FIG. 6 shows a specific example of the A / D converter 7. Comparator 6
_{1 to} 6 _n (n represents the number of gradations. In an a-bit A / D converter,
The respective reference voltage difference having a 2 ^a gradation), in order to vary between the upper comparator (e.g. 6 ₁ and 6 ₂₎ between the lower comparators (e.g. 6 _n-1 and 6 _n), the reference Voltage Vref.
a, Vref.b (Vref.1>Vref.a>Vref.b> Vref.2) are supplied from the intermediate tap. In order to obtain the input / output characteristics of the upwardly bent polygonal line as shown in FIG. 5, it is sufficient to supply voltages lower than the original voltage values of the intermediate taps supplying Vref.a and Vref.b.

FIG. 7 shows another example of the A / D converter 7. The circuit configuration is the same as that of the prior art shown in FIG. 4, but the resistance value of the resistor for generating the reference voltage of each comparator is set to (r, r ', r ") by that of the upper comparator and that of the lower comparator. In order to obtain the input / output characteristics of a polygonal line having an upward convex as shown in FIG. 5, the relationship of r> r ′> r ″ may be provided.

Next, specific examples of the digital signal processing circuit 8 are shown in FIGS. 8 and 9, respectively.

In FIG. 8, 50 (50 ₁ , 50 ₂ ) is a gain correction circuit, 51 is a coefficient circuit, 52 is a comparator, 53 is a reference level generator, and 54 is an arithmetic circuit.

Since the output of the A / D converter 7 is non-linear reduction in polygonal line shown in FIG. 5, the A _1, A ₂ levels shown in Figure 5 is generated from the reference level generator 53, such A _1, A ₂ comparing the level and the non-linear coded signal by the comparator 52, the coefficient if non-linear coded signal is a ₂ level or higher (a1 / a
The 3), A ₁ level or more, if A ₂ levels following coefficients (a1 / a
2), to enable the coefficient circuit 51 with the coefficient 1 if A ₁ level or less. That is, the signal which has been made non-linear by the broken line in FIG. 5 is returned to linear, and then the arithmetic circuit 54 digitally performs γ correction. In addition, the signal compressed by the broken line characteristic shown in FIG. 5 is expanded based on the low-level signal.
The operation can be performed with the number of effective bits greater than the number of bits of the D converter 7,
S / N degradation due to bit errors can be suppressed.

Next, a specific example of the digital signal processing circuit shown in FIG. 9 will be described. In the figure, 55 (55 ₁ , 55 ₂ ) is a gain correction circuit,
6 is an address generation circuit, 57 is a memory, and 58 is an arithmetic circuit. The address generation circuit 56 generates an address according to the output level of the A / D converter 7 and selects an address of the memory 57. Therefore, if data for linearization is input to the memory 57 in advance, it can be linearized by reading out the data by the address. A specific example of the linearization will be described below.

First, it is assumed that the input / output characteristics of the A / D converter 7 are shown in the broken line column of FIG.
3 shows the input / output characteristics of the A / D converter 3). Where A is A
Represents the input range of the / D converter 7. The input / output characteristics indicated by the polygonal lines in FIG. 10 are as follows: al = 2, a2 = 1, a3 in FIG.
= 0.5. At this time, the input / output characteristics of the A / D converter 7 are represented by a graph as shown in FIG. Here, region 1, region 2, and region 3 are arranged in ascending order of signal level.
Is defined.

FIG. 12 shows the read output characteristics for the addresses of the memory 57. In the area 1, the difference between adjacent levels is only the smallest bit, and the difference is 00001 = α. In region 2, the difference between adjacent levels is (a1 / a2) × α = 2α = 0
[0010] In the area 3, the difference between adjacent levels is (a1 / a3)
× α = 4α = 00100. If this is represented by a graph, the first
As shown in FIG. 3, the data compressed with the upward convex characteristic in FIG. 11 is expanded with the downward convex characteristic in FIG. 13, and the output of the memory 57 is the input of the A / D converter 7. The signal becomes linear with respect to the signal.

As is apparent from the above description, the number of gradations can be doubled in the area 1 where the signal level is small, the output of the memory 57 becomes a signal with one bit added, and the arithmetic circuit 58 can perform an accurate operation. Assuming that the number of bits of the A / D converter 7 is N,
N + (a1 / 2) -bit conversion is possible (if (a1 / 2) is not an integer, the fractional part may be rounded up).

FIG. 14 shows another example of performing signal compression using the polygonal line characteristics shown in FIG. In the figure, 59 (59 ₁ , 59 ₂ ) is a comparator, 60 is a reference voltage generating circuit, 110 is an operational amplifier, SW is a switch, and R and r are resistors (also showing resistance values). As is well known, the gain G of the amplifier circuit composed of the resistors R and r and the operational amplifier 110 shown in FIG. 14 is G ₁ = R / ｛r1 r2 r3 / when both switches SW1 and SW2 are conducting. (r1 r2 + r2 r3 + r3 r1)} when only the conductive state switches _{SW1, G 2 = R / {} r1 r2 / (r1 + r2)} switches SW1, SW2 are both G ₃ = R / r ₁ next time nonconductive, G ₁ > relationship of G _2> G _3.

On the other hand, the comparator 59 ₁ signal reference voltage A ₁ (A shown in FIG. 5
The switch SW2 large time than _one level) and non-conductive, the comparator 59 ₂ large time than the signal reference voltage A ₂ (A ₂ levels shown in FIG. 5) is the switch SW1 to the non-conducting state. _{Accordingly, G 1 = a1, G 2} = a2 choose appropriately the r1 to r3,
If G ₃ = a3, signal compression based on the broken line characteristic shown in FIG. 5 can be performed between the input and output of the circuit shown in FIG.

The above is a circuit configuration example focusing on γ correction, which is shown as a circuit configuration example useful for understanding the embodiment of the present invention,
An embodiment of the present invention focused on white balance will be described below.

FIG. 15 is a block diagram showing one embodiment (one embodiment of the present invention focused on white balance).
This embodiment is directed to a case where a primary color filter is used for the image sensor 1.

In the figure, 61 is a gain control circuit, 62 (62 _{1 to} 62 ₅ ) is an amplifier, G _{1 to} G ₅ are gain, 63 (63 ₁ , 63 ₂ ) are switches, and 64 (6 1
4 ₁ to 64 ₃ ) are A / D converters, 65 is a digital signal processing circuit, and A / D converter 64 is the A / D converter 7 in FIG.
The D converter 3 may be used.

Which is the output signal of the preamplifier _{2 (2 1 ~2 3) r} ( red), g
The signal levels of the (green) and b (blue) primary color signals vary with the color temperature as shown in FIG. 16 (a) even when a white subject is imaged. Therefore, the switch 63 is switched between when the color temperature is high and when the color temperature is low, and as shown in FIG.
The input range of the A / D converter 64 can be used effectively. After obtaining a rough white balance as shown in FIG. 16 (b), the subsequent digital signal processing circuit 65 adjusts the signal levels of r ', g', and b 'by calculation, thereby easily achieving a strict white balance. Can be taken.

The first embodiment in which complementary color filters W (transparent), Ye (yellow), C _Y (cyan), and G (green) are used in the image sensor 1 will be described.
Figure 7 shows. In the figure, 66 (66 _{1 to} 66 ₆ ) is an amplifier, 67
(67 _1, 67 ₂₎ switches, the gain control circuit 68, G ₁ ~G ₆ gain, 69 (69 ₁ to 69 ₄₎ is A / D converter, 70 is a digital signal processing circuit, 71 (71 ₁ to 71 ₆₎ coefficient circuit, 1 / G ₁ to 1 / G ₆ is a coefficient obtained by adding a factor circuit 71, 72 (72 _1, 72 ₂₎ are switches, 73 is an arithmetic circuit, a / D converter 69 (69 _{1 to} 69 ₄ ) may be the A / D converter 7 in FIG. 1 or the A / D converter 3 in FIG.

Complementary color signals w, y _e , _cy , g corresponding to color filters W, Ye, C _Y , G
When the color temperature changes, the 18th
The signal level changes as shown in FIG. Accordingly, FIG. 18 switches the switch 67 in the case when the color temperature is high and low and (b) show _{w ', y e', c} y ', g' input of them if the A / D converter 69 as The range can be used effectively. At the same time as the above switching, the switch 72 is switched, and w,
After returning to the levels of y _e , c _y , and g, the signal is input to the arithmetic circuit 73, and the arithmetic circuit returns the primary color signal, and the levels of the primary color signals are aligned to obtain a strict white balance.

FIG. 19 shows still another embodiment. In the figure, reference numeral 75 denotes a color temperature detection circuit, and the other components are the same as those in FIG. The color temperature detection circuit 75 detects whether the color temperature is high or low, and if high, connects the switches 67 and 72 to the upper side,
If lower, connect to lower side. At this time, if G ₂ > G ₃ and G ₅ > G ₄ , the characteristics shown in FIG. 18B can be obtained automatically. The embodiment of FIG. 15 can be similarly automated by the color temperature detection circuit 75.

In the above embodiment, the range of the color temperature is divided into two.
Needless to say, it can be achieved by similar means beyond the division. Further, since the signal levels of the signals w and g have relatively little change with respect to the color temperature change, only one amplifier 62, 66 and one coefficient circuit 71 are used. Therefore, two or more signals may be used and switched by a switch.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to this invention, the digital television camera which can reduce the deterioration of the S / N ratio accompanying the analog-digital conversion at the time of the analog-digital conversion performed in connection with taking the white balance, and has good image quality Equipment can be provided. Further, the number of bits of the A / D converter to be used can be made smaller than that of the conventional A / D converter.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration example of a digital television camera device useful for understanding an embodiment of the present invention, FIG. 2 is a block diagram showing a conventional example of a digital color camera, and FIG. FIG. 4 is a characteristic diagram showing input / output characteristics of various circuit elements constituting a digital color camera, FIG. 4 is a circuit diagram showing a configuration example of a conventional A / D converter, and FIG. 5 is an A / D that can be used in the present invention. 6 and 7 are circuit diagrams showing specific examples of the configuration of an A / D converter that can also be used in the present invention. FIG. 10 is a block diagram showing another example of the circuit configuration of the digital television camera device useful for understanding the embodiment of the present invention. FIG. 10 is an explanation based on data on the polygonal line characteristics of the A / D converter that can be used in the present invention. FIG. 11 shows an A / D converter that can also be used in the present invention. FIG. 12 is a characteristic diagram showing a specific example of a polygonal line characteristic, FIG. 12 is an explanatory diagram showing the correspondence between memory addresses and memory contents when a polygonal line characteristic is obtained by a memory, and FIG. 13 is a digital signal processing circuit that can be used in the present invention. FIG. 14 is a characteristic diagram showing a polygonal line characteristic to be given, FIG. 14 is a circuit diagram showing a specific example for realizing the polygonal line characteristic shown in FIG. 5, FIG. 15 is a block diagram showing an embodiment of the present invention, and FIG.
The figure is a characteristic diagram used to explain the circuit operation in FIG.
FIG. 17 is a block diagram showing another embodiment of the present invention, FIG. 18 is a characteristic diagram used for describing the circuit operation in FIG. 17, and FIG. 19 is a block diagram showing still another embodiment of the present invention. is there. Description of reference numerals 7 …… A / D converter, 8,65,70 …… Digital signal processing circuit,
61,68 …… Gain control circuit

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-58-40981 (JP, A) JP-A-60-154795 (JP, A) JP-A-61-280189 (JP, A)

Claims (3)

(57) [Claims] 1. An image sensor, a plurality of A / D converters for respectively performing analog-to-digital conversion of a plurality of video signals obtained from the image sensor, and outputs of the plurality of A / D converters. A digital signal processing circuit that performs digital processing by inputting a plurality of digital video signals, and a digital television camera device that includes at least a plurality of systems of video signals obtained from the image sensor. The amplifiers provided in the respective signal paths up to the respective input to the D converter, and the levels of the respective video signals input to the respective A / D converters via the respective amplifiers are substantially aligned. Thereby, in order to enable the effective use of the input range in each of the A / D converters, the gain switching of each of the amplifiers is performed by selecting an optimum one from combinations of predetermined amplifier gains. A fixed gain switching circuit to be performed, and a means for adjusting the level of each video signal, which has been input through the respective A / D converters, and which have substantially the same level, to obtain a white balance. A digital television camera device, comprising: a digital signal processing circuit. 2. A digital television camera device according to claim 1, further comprising: a color temperature detecting circuit for detecting a color temperature of illumination light for an object to be imaged, wherein said gain switching circuit controls said gain temperature in accordance with the color temperature detected by said detecting circuit. A digital television camera device, wherein the gain of the amplifier is switched. 3. A digital television camera device according to claim 1, wherein a complementary color filter is used for said image sensor, and a complementary color video signal is input to said A / D converter. Television camera device.