JPH0223778A - digital television camera equipment - Google Patents

Abstract

PURPOSE:To reduce the deterioration of S/N due to s bit error caused by digital signal processing by using the A/D converter of an input/output characteristic non-linearized by a polygonal line. CONSTITUTION:A video signal from an image pickup element 1 is given to the A/D converters 71, 72 respectively through preamplifiers 21, 22. Here, the converters 71, 72 have the input/output characteristics non-linearized by the polygonal line as shown in a figure. Then, digital video signals from the converters 71, 72 are supplied to a digital signal processing circuit 8. The processing circuit 8 returns them into linear signals by adding the opposite coefficients of y=(1/a1)x, y=(1/a2)x, y=(1/a3)x by gain correction circuit 100a, 100b. Next, an arithmetic operation circuit 101 performs gamma-correction after operating white balance, etc.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an image sensor, an A/D converter that converts a video signal obtained from the image sensor from analog to digital, and
The present invention relates to a digital television camera device comprising a digital signal processing circuit that processes a digital video signal that is the output of a /D converter, and more specifically, The present invention relates to such a digital television camera device that makes it possible to reduce deterioration of the S/N ratio due to pit errors caused by pit errors.

[Prior Art] In recent years, digitalization of electronic circuits has progressed and is becoming widespread in the field of television cameras. The advantage of digitizing the signal system of television cameras is that large-scale integration has become easier with the rapid improvement of semiconductor manufacturing technology, simplifying the signal system, and signal processing unique to television cameras. One example is that white balance and gamma correction can be performed accurately and easily using calculations.

FIG. 2 shows a block diagram of an example of the configuration of a digital color camera. The same figure is also shown in Fig. 1 of Japanese Unexamined Patent Publication No. 61-280189, where 1 is an image sensor, 2 (2,, 2
□) is a preamplifier, 3 (33□) is an analog-to-digital converter (A/D converter), 4 is a digital signal processing circuit,
5 is a digital-to-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 to a digital signal by the A/D converter 3, and the digital signal processing circuit 4 demodulates the color signal, white balance, γ correction, etc. With unique signal processing,
The D/A converter 5 converts it back to an analog signal. In addition, 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, but this does not mean that in the case of a color camera, it is necessary to use multiple systems. There is no need to be particular about the two systems, as this is the meaning shown.

[Problem to be solved by the invention]

The above-mentioned conventional technology includes signal processing unique to television cameras (i) nonlinear signal processing, i.e., γ correction;
) White balance was not considered.

Here, γ correction refers to the transmission and reception system of televisions, which uses imaging cameras and picture tubes in which the relationship between the input target output is not linear during various conversion processes, so it is It is necessary to perform correction in advance, and white balance refers to such correction.
It is well known that this is an adjustment that adjusts the levels of three channel signals so that an achromatic (white) image is obtained from bright to dark areas.

First, (1) γ correction will be explained using FIG. 3.

The figure (a) 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 (b) shows the input of the A/D converter 3.
(C) shows the input/output relationship of the /D converter 3, and (C) shows the input/output relationship of the digital signal processing circuit 4. A video signal proportional to the amount of incident light is input to the A/D converter 3, and the A/D converter 3
It will be understood from FIGS. 3(a) and 3(b) that the converter 3 also outputs a digital signal proportional to the input signal.

At this time, a bit error Δ1. which occurs due to a quantization error (quantization noise) when analog-to-digital conversion is performed by the A/D converter 3. Δ2 is input to the digital signal processing circuit 4 as is.

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).
As seen in That is, the bit error Δ1 that occurs when the signal amount is small is magnified in the output of the signal processing circuit 4, and conversely, the bit error Δ2 that occurs when the signal amount is large is reduced. Therefore, the S/N ratio when the signal amount is small deteriorates, and furthermore, the S/N
If a digital signal with a degraded ratio is used for calculations, the S/N will be higher.
There was a problem that the ratio deteriorated.

Furthermore, as shown in Fig. 3(d), if the input/output characteristics of the A/D converter 3 are made the same as those of the γ correction (y- It needs to be small, and generally requires accuracy exceeding the input resolution of the A/D converter 3. That is, it is necessary to match the resistance value of the reference resistor r for creating the quantization step of the input section of the A/D converter 3 shown in FIG. 4 with very high precision.

In addition, in the same figure, Vref, 1, Vref
, 2 is the reference voltage, ■ is the input terminal, 6 (6,, 6□,
...6,) are comparators, in which the analog signal input from the input terminal I becomes a digital signal and is sent to the comparators 6I to 6. This is the output from .

Furthermore, when the input signal to the A/D converter 3 is a plurality of complementary color signals (for example, cyan, magenta, etc.), white balance can be achieved when the signal amounts of each of the plurality of complementary color signals are different. Corrections cannot be made.

Next, (ii) white balance will be explained.

For television cameras, the color temperature of the illumination light is generally 30.
It is necessary to maintain white balance even if the angle changes within a range of about 00 to 10,000 degrees. When the color temperature changes within the above range, the image sensor 1. The signal output level of the preamplifier 2 changes from double to half. Therefore, A/D
There is a problem in that the input range of the converter 3 cannot always be used effectively and the S/N ratio deteriorates due to bit errors.

When the color filter used in the image sensor 1 is a primary color filter, the image sensor 1. Since the output signal of the preamplifier 2 is a plurality of primary color signals, the signal levels of the plurality of primary color signals are matched (after white balance is taken) before A.
If the input range is input to the A/D converter 3, the input range of the A/D converter 3 can be used effectively at all times, but an analog circuit for white balance is required, which increases the circuit scale, and requires digital calculations. It is difficult to improve performance compared to when white balancing is performed. Furthermore, when a plurality of complementary color signals are manually input to the A/D converter 3 using a complementary color filter, white balance cannot be achieved by matching the signal levels, as described above.

An object of the present invention is to provide a digital television camera device that can reduce deterioration of the S/N ratio due to bit errors caused by the above-mentioned signal processing unique to television cameras.

[Means to solve the problem]

The above purpose is achieved by, as a first means, making the input/output characteristics of the A/D converter 3 non-linear, which can be represented by a polygonal line, as shown in FIG. This is achieved by linearizing the image again at , performing calculations such as white balance, and applying T processing in the calculation.

In FIG. 5, the slope al in each polygonal line area.

a2. a3 is a constant, and there is a relationship of at > a2 > a3.

Here, the overall characteristics are approximated by three polygonal lines, but there is no need to stick to just three. In addition, an amplifier having the input/output characteristics shown in FIG. 5 is provided before the input of the A/D converter 3, and the A/D
The same effect can be achieved even if the input/output characteristics of the converter 3 are the same as the conventional ones as shown in FIG. 3(b).

As a second means, an amplifier is provided at the front stage of the input of the A/D converter 3, and the gain of this amplifier can be selected discretely (N types), and a rough white balance is achieved using the above N types of gains. This is achieved by correcting the above gain using a digital signal processing circuit and then achieving accurate white balance.

[Effect]

If the input/output characteristics of the A/D converter 3 are set to the input/output characteristics shown in FIG. 5, the above-mentioned SZN ratio deterioration is alleviated because many gradations are taken in advance when the amount of input signal is small. Furthermore, if the gradient a1 in the polygonal line region is set to be about 3 or less at most, the accuracy required for the reference resistance of the input section described above can be achieved with the current process technology.

In addition, non-linearization using a polygonal line makes it easier to return the signal to a linear signal with respect to the amount of incident light using a digital signal processing circuit, and also makes it easier to align the characteristics of a plurality of A/D converters.

Furthermore, if the white balance is roughly maintained, even if not accurately, the input range of the A/D converter 3 can be effectively utilized, and the above-mentioned S/N ratio deterioration can be reduced. At this time, A/D
Since the gain of the amplifier at the stage before the converter 3 can be selected from among the N11t class, it becomes easy to correct it in the digital signal processing circuit at the rear stage.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. In the figure, 1 is an image sensor, 2 (2, 2□) is a preamplifier, 5 is a D/A converter, and 7 (7, 7□) is an input/output characteristic that has a polygonal line characteristic as shown in Figure 5. 8 is a digital signal processing circuit, 100 (1003,
100g) is a gain correction circuit, and 101 is an arithmetic circuit.

Components that can be used in common with the conventional example shown in FIG. 2 are given the same reference numerals. Further, although the number of output lines of the image sensor 1 and the number of preamplifiers 2 are set to two each, there is no need to limit the number to two. Gain correction circuit 100 (100+) in digital signal processing circuit 8.

1002), y=(1/al)x, y=(1/a2)x
.

An inverse coefficient such as y=(1/a3)x is added to return the signal to a linear signal, and the arithmetic circuit 101 performs calculations such as white balance, and then performs γ correction.

FIG. 6 shows a specific example of the A/D converter 7. The reference voltage difference of each of the comparators 61 to 67 (n represents the number of gradations; an a-bit A/D converter has 2I'' gradations) is set between the upper comparators (for example, 61 and 6□). In order to differ between the lower comparators (e.g. L-1 and 6.), the reference voltages Vref,a, Vref,b (V
ref, 1>Vref, a>Vref, b>Vr
ef, 2) is supplied from the intermediate tap. In order to obtain the input/output characteristics of the upwardly convex polygonal line as shown in Figure 5, V
It is sufficient to supply voltages lower than the original voltage values of the intermediate taps that supply ref, a, Vref, and b, respectively.

FIG. 7 shows another example of the A/D converter 7. The circuit configuration is the same as the conventional example shown in FIG.
) as shown in Figure 5.
It is good to have the following relationship.

Next, specific examples of the digital signal processing circuit 8 are shown in FIGS.
Each is shown in the figure.

In FIG. 8, 50 (50, 50□) 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 made nonlinear according to the polygonal line shown in FIG. 5, the AI shown in FIG.

The A2 level is generated from the reference level generator 53, the A + A z level and the non-linearized signal are compared by the comparator 52, and the non-linearized signal is
If the level is 2 or above, the coefficient (al/a3) is enabled in the coefficient circuit 51; if the level is A, if it is above the level A2, then the coefficient (al/a2) is enabled; if the level is A, if it is below the level A, the coefficient 1 is enabled in the coefficient circuit 51. . That is, after the signal that has been made non-linear along the polygonal line in FIG. 5 is returned to linear, the arithmetic circuit 54 digitally performs the γ correction. Moreover, since the signal compressed according to the polygonal characteristic shown in FIG. It is possible to perform calculations and suppress S/N deterioration due to bit errors.

Next, a specific example of the digital signal processing circuit shown in FIG. 9 will be explained. In the figure, 55 (55, 55□) is a gain correction circuit, 56 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
Select address 7. Therefore, if data for linearization is input into the memory 57 in advance, it can be linearized by reading it using the address. A specific example of the above linearization will be explained below.

First, assume that the input/output characteristics of the A/D converter 7 are shown in the line column in FIG. 10 (for comparison, the input/output characteristics of the conventional A/D converter 3 are shown in the linear column). ). Here, A represents the input range of the A/D converter 7. The input/output characteristics shown in the line column in Figure 10 are
=2. This is the case when a2-1 and a3=0.5. At this time, the turnout characteristics of the A/D converter 7 can be expressed graphically as shown in FIG. 11. Here, area 1, area 2, . Define it as area 3.

FIG. 12 shows read output characteristics with respect to addresses of the memory 57. In region 1, adjacent levels differ only in the minimum bit, and the difference is 00001=α. In region 2, the difference between adjacent levels is (al/a2)X
α-2α-00010, in region 3, the difference between adjacent levels is (al/a3)Xα-4α=OO100.

If this is expressed as a graph, it will look like Figure 13.
The data compressed using the characteristic convex upward in the figure is expanded according to the characteristic convex downward downward in FIG. 13, and the output of the memory 57 is
The signal becomes linear with respect to the input signal of the converter 7.

As is clear from the above explanation, the number of gradations is doubled in region 1 where the signal level is small, the output of the memory 57 becomes a signal with 1 bit added, and the arithmetic circuit 58 can perform accurate calculations. If the number of bits of the A/D converter 7 is N, it is possible to convert it into N+ bits (if is not an integer, it is sufficient to round up the decimal point).

Another example of signal compression using the polygonal line characteristic shown in FIG. 5 is shown in FIG. In the same figure, 59 (59,,59
□) is a comparator, 60 is a reference voltage generation circuit, 110 is an operational amplifier, SW is a switch, and R and r are resistors (resistance values are also shown). As is well known, the resistances R, r, shown in FIG.
The gain G of the amplifier circuit composed of the operational amplifier 110 is as follows: When both the switches SWI and SW2 are in a conductive state, when only the switch SWI is in a conductive state, and when both SW2 are in a non-conductive state, G3= and I, and Gr > There is a relationship of Gz >03.

On the other hand, comparator 59. When the signal is higher than the reference voltage A (A1 level shown in FIG. 5), the switch SW2 is made non-conductive, and the comparator 59□ sets the signal to be higher than the reference voltage A 2 (
A2 level shown in Fig. 5), switch SW
1 becomes non-conductive. Therefore, if r1 to r3 are appropriately selected and G,=al, G2-a2, G3-a3, the signal compression by the polygonal line characteristic shown in FIG.
This can be done between the input and output of the circuit in Figure 4.

The above is an example focusing on γ correction, and an example focusing on white balance will be described below.

FIG. 15 is a block diagram showing one embodiment thereof. This embodiment takes as an example a case where primary color filters are used in the image sensor 1.

In the figure, 61 is a gain control circuit, 62 (62° to 62°
5) is the amplifier, G1-G5 is the gain, 63 (63, , 63
□) is a switch, 64 (64, ~ 643) is an A/D
The converter 65 is a digital signal processing circuit, and the A/D converter 64 may be the A/D converter 7 in FIG. 1 or the A/D converter 7 in FIG.
Converter 3 may also be used.

r (red) which is the output signal of preamplifier 2 (21 to 23)
The signal levels of the 2g (green) and b (blue) primary color signals change depending on the color temperature, as shown in FIG. 16(a), even when a white subject is imaged. Therefore, the input range of the A/D converter 64 can be effectively utilized by switching the switch 63 depending on whether the color temperature is high or low, as shown in FIG. 16(b).

After roughly adjusting the white balance as shown in FIG. 16(b), the subsequent digital signal processing circuit 65 performs rr,
By calculating the signal levels of gl and b', it is possible to easily obtain a precise white balance.

FIG. 17 shows an example in which complementary color filters W (transparent), Ye (yellow), CY (cyan), and G (green) are used in the image sensor 1. In the same figure, 66 (66, ~666)
is an amplifier, 67 (67,,67°) is a switch, 68 is a gain control circuit, G, ~G6 is a gain, 69 (69, ~69
4) is an A/D converter, ■0 is a digital signal processing circuit, 7
1 (71, to 716) are coefficient circuits, 1/G1 to 1/G6
is the coefficient added by the coefficient circuit 71, 72 (72,,7
2□) is a switch, 73 is an arithmetic circuit, and the A/D converter 69 (69, to 694) may be the A/D converter 7 in FIG. 1 or the A/D converter 3 in FIG. 2.

Complementary color signals W corresponding to color filters W, Ye, C, ,G,
When the color temperature of yet Cy,g changes, the signal level changes as shown in FIG. 18(a) even when a white subject is imaged. Therefore, by switching the switch 67 depending on whether the color temperature is high or low, the input range of the A/D converter 69 can be made valid by setting W' + Va' + cV'g' as shown in FIG. 18(b). available for use.

At the same time as the above switching, the switch 72 is switched to return the signal to the level of w+ )' 11 + cY +g, and then input it to the arithmetic circuit 73, where the arithmetic circuit converts it back to the primary color signal and makes the levels of the primary color signal equal. Accurate white balance.

FIG. 19 shows yet another embodiment. In the figure, 75 is a color temperature detection circuit, and the other parts are the same as in FIG. 18. The color temperature detection circuit 75 detects whether the color temperature is high or low, and when the color temperature is high, the switches 67 and 72 are connected to the upper side, and when it is low, the switches 67 and 72 are connected to the lower side. At this time Gz
>G3, Gs >G4, Figure 18(b)
characteristics can be obtained automatically. The embodiment shown in FIG. 15 can also be automated using the color temperature detection circuit 75.

In the above embodiment, the color temperature range is divided into two, but it goes without saying that division into three or more can be achieved using similar means. Further, since the signal w+g has relatively little change in signal level with respect to color temperature change, only one amplifier 62, 66 and one coefficient circuit 71 are used, so two or more may be used and switched by a switch.

〔Effect of the invention〕

According to the present invention, S
The deterioration of the /N ratio can be reduced, and a digital television camera device with good image quality can be provided. Furthermore, the number of bits of the A/D converter used can be made smaller than in the conventional case, which has the effect of making the device more compact and lowering power consumption.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing a conventional example of a digital color camera, and Fig. 3 is a block diagram showing an example of a conventional digital color camera.
The figure is a characteristic diagram showing the input/output characteristics of various circuit elements constituting a conventional digital color camera, FIG. 4 is a circuit diagram showing an example of the configuration of a conventional A/D converter, and FIG. A characteristic diagram showing an example of input/output characteristics of a /D converter, FIG.
FIG. 7 is a circuit diagram showing a specific example of the configuration of an A/D converter used in the present invention, FIGS. 8 and 9 are block diagrams showing other embodiments of the present invention, and FIG. An explanatory diagram based on data of the polygonal line characteristics of the A/D converter used in the present invention, FIG. 11 is a characteristic diagram showing a specific example of the polygonal line characteristic of the A/D converter used in the present invention, and FIG. FIG. 13 is a characteristic diagram showing the polygonal line characteristics given to the digital signal processing circuit used in the present invention, and FIG. 14 is an explanatory diagram showing the correspondence between memory addresses and memory contents when obtaining FIG. 15 is a block diagram showing another embodiment of the present invention, FIG. 16 is a characteristic diagram used to explain the circuit operation in FIG. 15, and FIG. 17 is a diagram showing a further embodiment of the present invention. FIG. 18 is a block diagram showing another embodiment. FIG. 18 is a characteristic diagram used to explain the circuit operation in FIG. 17. FIG. 19 is a block diagram showing still another embodiment of the present invention. Explanation of symbols 7... A/D converter, 8, 65.70... Digital signal processing circuit, 61.68... Gain control circuit agent
Patent Attorney Akio Namiki J 9 Fig. fig., 551 Fig. fig.

Claims (1)

[Claims] 1. An image sensor, an A/D converter that converts a video signal obtained from the image sensor from analog to digital, and a digital video signal that is the output of the A/D converter. In a digital television camera device comprising at least a digital signal processing circuit that performs digital processing, the A/D converter or a circuit at a stage preceding the A/D converter includes an output signal corresponding to an input signal level. In a certain first range where the level relationship is low, the input signal level is low, the first slope a1
In a second range where the input signal level is higher than that, it is linear with a second slope a2, and in a third range where the input signal level is higher than that, it is linear with a third slope a3. Similarly, in the n-th range where the input signal level is highest, it is linear with the n-th slope an, and the relationship a1>a2>a3>...>an holds true. The digital signal processing circuit is provided with characteristics of the output signal level relative to the input signal level (hereinafter referred to as compression characteristics) such that the relationship between the output signal level and the input signal level is such that the input signal level is low. In the first range, the first slope b1
In a second range where the input signal level is higher than that, it is linear with a second slope b2, and in a third range where the input signal level is higher, it is linear with a third slope b3. Similarly, in the nth range where the input signal level is highest, it is linear with the nth slope bn, and the relationship b1<b2<b3<...<bn holds. A digital television camera device characterized by having characteristics of the output signal level with respect to the input signal level (hereinafter referred to as expansion characteristics) such that
is an integer). 2. In the digital television camera device according to claim 1, the expansion characteristic is provided only in a large signal level range of the video signal in the digital signal processing circuit, and the digital video obtained from the A/D converter is A digital television camera device characterized in that it obtains a digital video signal with a greater number of bits than the number of bits of the signal. 3. An image sensor, a plurality of A/D converters that convert the plurality of video signals obtained from the image sensor into analog and digital, and a plurality of A/D converters that are the outputs of the plurality of A/D converters. A digital television camera device comprising at least a digital signal processing circuit that receives an input digital video signal and performs digital processing, an A/D converter to which multiple systems of video signals obtained from the image pickup device correspond. An amplifier is provided in each signal path until the signal is input to the respective A/D converters. Gain switching is performed, and in the digital signal processing circuit, the levels of the video signals input through each A/D converter and whose levels are roughly aligned are returned to the original signal levels before the levels were aligned. This digital television camera device is characterized in that it further accurately aligns the levels of each video signal to achieve white balance. 4. The digital television camera device according to claim 3, further comprising: a color temperature detection circuit for detecting the color temperature of illumination light for an object to be imaged; and switching the gain of the amplifier according to the color temperature detected by the detection circuit. Features of digital television camera equipment. 5. In the digital television camera device according to any one of claims 1 to 4, a complementary color filter is used in the image sensor, and a complementary color video signal is input to the A/D converter. Features of digital television camera equipment.