RU2428810C1 - Television camera for viewing in conditions of low illumination and/or low brightness of objects - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: primary generation of components of a video signal of a composite image is performed in charge form in parallel on two targets of one CCD matrix at different exposure (accumulation) times and different amplification coefficients of video amplifiers. ^ EFFECT: wider dynamic range and high geometrical accuracy of forming the output image of a television camera by optimising light-to-signal conversion and performing said conversion on a single photodetector crystal. ^ 6 dwg

Description

The present invention relates to cameras made on the basis of the light-to-signal converter in the form of a matrix of charge-coupled devices (CCD matrices) and operating in conditions of complex lighting and / or complex brightness of objects. These conditions mean that in the field of view of the camera can be simultaneously strongly and dimly lit objects and / or objects with a sharp difference in brightness.

The closest in technical essence to the claimed invention should be considered a camera [1], containing sequentially located and optically coupled lens and a beam splitter, the first beam splitter output being optically connected to the photo target of the first television signal sensor, and the second beam splitter output to the photo target of the second television signal sensor, the geometrical sizes of the photo target of the sensors are the same, and the projections of the optical frame of the lens on the photo target coincide, while on the photo target of the second sensor a technological mask is applied, which provides an opacity “window” for the input light flux; as well as serially connected signal shaper “frame” and “window” and a switch-mixer, the first information input of which is connected to the output of the first sensor, the second information input to the output of the “video” of the second sensor, and the first and second control inputs, respectively, to the output the signal “window” and the output of the signal “frame” of the shaper, the output of the switch-mixer being the output of the “video” camera, and the spatial position of the “window” of opacity and its geometric dimensions correspond to the time dimension displacement in the raster and parameters in time units for the electronic “frame” and the electronic “window”.

A typical example of the operating conditions for the prototype is the monitoring of the hot-rolled zone in metallurgy, as well as the control of the processes of arc or electron beam welding in automatic or semi-automatic mode.

The prototype camera generates a composite video signal of the combined image, which is the result of the synthesis of images produced by the first and second sensors.

For the prototype device, the following features are expected:

- the first and second sensors are synchronized in Genlock mode according to the receiver synchronization signal (MSS) from one of them;

- the first and second sensors separately contain a CCD matrix, a signal processor and a control pulse generator, consisting of a series-connected time controller and level converters;

- CCD matrices are made according to the circuit organization “line transfer”;

- the signal processor provides the formation of a composite image signal, automatic gain control (AGC) of the video signal and the formation of a control signal for the automatic storage time adjustment unit (ARVN) of the photodetector;

- service pulses necessary for the signal processor to work, served through the control input from the output of the temporary controller;

- the ARVN unit is part of the control pulse generator, and its output signal with a variable duration is fed directly to the electronic shutter of the CCD matrix located on its photodetector section;

- synchronization pulses of horizontal and frame frequencies, necessary for the operation of the “frame” and “window” signal conditioners, can be taken directly from the outputs of these signals in the temporary controller.

The disadvantage of the prototype is the limitation of the dynamic range of the image of the camera due to the limited conversion capabilities of the light-signal and the lack of geometric accuracy in the formation of the output video signal of the combined image due to the use of two CCD matrices as photodetectors.

The objective of the invention is the expansion of the dynamic range and increase the geometric accuracy of the formation of the output image of the camera by optimizing the conversion of the light-signal "and performing it on a single crystal photodetector.

The problem is solved in that in the inventive camera, which contains sequentially located and optically coupled lens and a beam splitter, and the first output of the beam splitter is optically connected with the photo target of the CCD with the organization "line transfer", consisting of sequentially connected by charge communication of the first photodetector section, the first horizontal register and the first block conversion of charge into voltage (BPS), as well as a control pulse generator, consisting of series-connected time of the controller (VC) and level converters (PU), a signal conditioner “frame” and “window” and a switch-mixer, with the first and second outputs of the PU connected respectively to the control inputs of the first photodetector section and the first horizontal register of the CCD, and the third output PU - to the electronic shutter of the first photodetector section, the output of the first CCD sensor of the CCD is connected through the first information input of the signal processor to the information input of the first video amplifier, the control input of which is m of the input of the signal processor, connected to the second output of the VC, the first control input of which is connected to the first control output of the signal processor, the first information output of which is the video output of the first video amplifier, connected to the first information input of the mixer-mixer, the output of which is the output video ”cameras, the first and second control inputs of the switch-mixer are connected respectively to the output of the“ window ”signal and to the output of the“ frame ”signal of the former, the lowercase input and the input the frame synchronization of which is connected respectively to the outputs of the lowercase and frame sync pulses of the VK; as well as a second video amplifier and a second photodetector section, a second horizontal register and a second CCD, sequentially connected by charge coupling, the second photodetector section, the geometric dimensions of which coincide with the geometric dimensions of the first photodetector section, is optically connected to the second output of the beam splitter, and a technological mask is applied to it, providing for the input light flux a “window” of opacity, the spatial position of which and its geometric dimensions correspond to the time In the raster and parameters in time units for the electronic “frame” and the electronic “window”, the second photodetector section, the second horizontal register and the second SPS are introduced into the CCD matrix crystal, and the second video amplifier is introduced into the signal processor, and the control inputs of the second photodetector sections and the second horizontal register are connected respectively to the first and second outputs of the control unit, and the electronic shutter of the second photodetector section is connected to the fourth output of the control unit, the output of the second SPS of the CCD matrix through the second information the input signal processor is connected to the information input of the second video amplifier, the control input of which is connected to the control input of the signal processor, the second control output of which is connected to the second control input of the VC, the video output of the second video amplifier, which is the second information output of the signal processor, is connected to the second information Valid mixer switch, wherein the gate area ΔS ₁ FET performing the charge carriers in the first charge BPZN is formed by the criterion ma maximum DUTY control the charge capacity conversion, and the shutter area ΔS ₂ similar FET in the second BPZN - according to the criterion of the minimum entry in the intrinsic noise of the image signal, wherein ΔS _1> ΔS _2.

Comparative analysis with the prototype shows that the inventive television camera is characterized by the following features:

- mutual arrangement of the photo targets for the first and second photodetectors, because structurally and technologically, these targets are made in the form of two photodetector sections placed on a common crystal of a single CCD;

- the mutual arrangement of the first and second horizontal registers placed on a common crystal of a single CCD matrix;

- the mutual arrangement of the first and second CPS located on a common crystal of a single CCD matrix;

- circuitry organizations of a two-channel photodetector as a form of implementation of this element - a CCD matrix;

- mutual arrangement of the first and second video amplifiers, placed on a common signal processor of the camera;

- a constructive difference between the first and second overvoltage arresters in terms of the gate area of the field effect transistor, which performs element-by-element collection of charge image carriers.

The combination of known and new features is not known from the prior art, therefore, the claimed solution meets the requirement of novelty.

In the proposed solution, the primary formation of the components of the video signal of the combined image is performed in a charge form in parallel on two targets of the same CCD matrix at different exposure times and different amplification factors of the video amplifiers that are optimal or close to the optimal values for each of the transmitted fragments of the scene.

Due to the use of a single CCD matrix as the camera’s camera, the claimed camera does not have a spatial displacement error for the composite video signal components, the possibility of which in the prototype is fundamentally preserved due to the external synchronization error of the first and second television signal sensors. The stability of maintaining the amplitude of the video signal of the combined image is also increased when the camera is operated in the temperature range due to the effect on the photodetector of only one, and not two different readings of the CCD dark current density.

Due to the optimization in the photodetector of the “charge-voltage” conversion for dark and / or low-lit scene details, an additional expansion of the dynamic range is provided in the video output signal of the camera.

According to the technical result and methods for its achievement, the claimed solution meets the requirement of inventive step.

Figure 1 shows the structural diagram of the inventive camera; figure 2 shows a functional diagram of the technological organization of the CCD matrix; figure 3 shows an example of the placement of the components of the combined image in a television raster and the corresponding position and size of the "window" of opacity on the second photodetector section of the CCD; figure 4 presents a typical light characteristic of a television camera; 5 is a timing chart illustrating the electronic shutter control of the photodetector section of a CCD; figure 6 shows an illustration of the process of anti-blooming drain in the photodetector section of a three-phase CCD.

The inventive camera (see figure 1), contains sequentially located and optically coupled lens 1, a beam splitter 2, and a CCD matrix 3, consisting of a series of charge-coupled first photodetector sections 3-1, the first horizontal register 3-2 and the first BPZN 3- 3, as well as from the second photodetector section 3-4, the second horizontal register 3-5 and the second BPZN 3-6 located on the chip matrix and sequentially connected by charge coupling, the first output of the beam splitter 2 is optically coupled to the photodetector section 3-1, and the second beam splitter 2 output - with photodetector section 3-4; as well as a generator 4 of control pulses, consisting of series-connected VK 4-1 and PU 4-2; a signal processor 5 comprising a first video amplifier 5-1 and a second video amplifier 5-2; driver 6 signals "frame" and "window" and the switch-mixer 7, and the first output of the PU 4-2 is connected to interconnected control inputs of sections 3-1 and 3-4, the second output of the PU 4-2 to interconnected the control inputs of the horizontal registers 3-2 and 3-5, the third output of the PU 4-2 to the electronic shutter of section 3-1, and the fourth output of the PU 4-2 to the electronic shutter of section 3-4; BPZN 3-3 output is connected through the first information input of the signal processor to the information input of the video amplifier 5-1, and BPZN 3-6 output through the second information input of the signal processor 5 is connected to the information input of the video amplifier 5-2, the control input of which is combined with the control input of the video amplifier 5-1 is the control input of the signal processor 5, which is connected to the second output of the VK 4-1, the first control input of which is connected to the first control output of the signal processor 5, and the second control input of the VK 4-1 - to the second control output of the signal processor 5, the first information output of which is the video output of the video amplifier 5-1 connected to the first information input of the mixer-mixer 7, and the second information output of the signal processor 5, which is the video output of the video amplifier 5- 2, - to the second information input of the switch-mixer 7, the first and second control inputs of which are connected respectively to the output of the “window” signal and to the output of the “frame” signal of the driver 6, the lowercase input and the frame sync input ronizatsii which are respectively connected to the outputs of the horizontal and vertical sync pulses VC 4-1, wherein the outlet of the mixer-output switch 7 is "video" cameras.

The lens 1 and the beam splitter 2 in execution do not differ from similar blocks of the prototype. The beam splitter 2 (see Fig. 1) contains sequentially located and optically connected translucent mirror 2-1 and a reflecting mirror 2-2, the input of the translucent mirror being the input of the beam splitter, and the second output of the translucent mirror and the reflecting output, respectively, of the first and second outputs of the beam splitter .

The photodetector sections 3-1 and 3-4 (see FIG. 2) of the photodetector 3 have a typical design for CCD arrays with the organization of “horizontal transfer”. Each of them provides the accumulation of charge packets in photosensitive elements, which are used as photodiodes organized in columns. In the immediate vicinity of each column of photodiodes there is a light-sensitive vertical CCD register, separated from the photodiodes by a photocell. During the accumulation of charge packets in the photodiodes, a low voltage level is applied to the photocell, which provides a potential barrier between the photodiodes and the vertical CCD register. At the end of the accumulation, a high voltage level is briefly applied to the photocell, allowing the transfer of charge packets from the photodiodes to potential wells formed in vertical CCD registers.

As in the prototype, each of the photodetector sections of the CCD matrix 3 is equipped with an electronic shutter that performs electronic sensitivity adjustment by controlling the accumulation time of charge carriers during the personnel period. The pulse signal supplied to the corresponding control electrode is shown in FIG. 5b with respect to the frame blank shown in FIG. 5a. In fact, the electronic shutter is a shutter of the anti-blooming (sink) region GA, technologically performed in the photodetector section of the CCD, as shown in Fig.6.

During the light overload of the CCD, a high level of pulse bias is applied to the GA shutter, so the potential barrier is removed, the shutter opens, and photoelectron accumulation is excluded on the target. Charge carriers, not lingering in potential wells under phase electrodes, for example, under Ф2Н buses with three-phase transfer organization, rush into deeper wells created by the potential DA of the drain region, and then recombine into the photodetector substrate (see Fig.6b). When the light overload of the CCD is eliminated, the lower level of the pulse bias is applied to the shutter GA, closing it and realizing the accumulation mode with a reduced time T _for carrier collection inside the frame (see Fig. 6a).

Continuing the presentation of the operation of the photodetector 3 of the camera, we note that the charge packets from the vertical CCD registers of section 3-1 are transferred line by line to the horizontal register 3-2, from which they are read out element-wise through the CPS 3-3. Charge packets from the vertical registers of section 3-4 similarly go to the horizontal register 3-5, and then to BPZN 3-6. All of them are also typical representatives of the CCD matrix with line wrap.

Block 3-6, like block 3-3, is designed to convert the charge signal of the image into the voltage of the video signal. Their principal difference is the different level of charge packets at the input, which is taken into account in the design of the field effect transistor in terms of the capacitance of its gate.

A high level of the charge signal is expected for CWP 3-3; therefore, it is necessary to increase the control ability of the unit by increasing the gate area (ΔS ₁ ). On the contrary, a low level of the charge signal is assumed for BPS 3-6, therefore, the shutter capacity should be extremely small, which is achieved by choosing a geometry of its size that provides a small area (ΔS ₂ ). So, the condition: ΔS ₁ > ΔS _{2 is} mandatory when designing load transistors.

Here it is necessary to provide a technical justification for this proposal. The fact is that in each element of the video signal output from the CCD matrix, in addition to the photon noise, an intrinsic noise source, called read noise, appears. The standard deviation (RMS) of the read noise is determined by the gate area of the output field effect transistor. The typical value of the standard deviation of reading noise is 20 electrons [2, p.52], and it is the result of designing an output transistor, the gate area (ΔS) of which contains the maximum value of the expected charge, i.e. meets the criterion of maximum control ability of the charge photoelectronic conversion carried out in the CCD matrix.

According to experts, theoretically, the standard deviation of read noise can be reduced by an order of magnitude [2, p. 52]. Therefore, the reason for limiting the lower dynamic range for the prototype camera is already inherent in the design of the CCD array of the CCD, and to expand the dynamic range it is advisable to optimize the charge-voltage conversion process in the photodetector.

On the light characteristic of the claimed camera (see figure 4), point B corresponds to the minimum (threshold) illumination of the camera E _min2 for the threshold signal-to-noise ratio ψ _pore. = 6, when the shutter area ΔS _{2 is} selected according to the criterion of the minimum introduction of the intrinsic noise of the matrix into the video signal. Point A on the same characteristic corresponds to the minimum illumination E _min1 for the same threshold signal-to-noise ratio ψ _pore = 6, and the area ΔS _{2 is} selected according to the criterion of the maximum control ability of the charge conversion. Therefore, the ratio of threshold illuminances can be:

In fact, in the claimed solution, two CCD arrays with horizontal transfer and optimized charge-voltage conversion for each of them are placed on a common photodetector chip. Assume that for a number of CCD elements sections 3-1 and 3-2 is 582 (V) × 752 (H), and the size of each target diagonally - _^1/2 inches.

Another feature of the proposed solution is the creation on the photodetector section 3-4 of the “window” of opacity for the light flux by applying a technological mask to the photo target.

The spatial position of the “window” of opacity should correspond to the position in the raster of the television camera of the electronic “frame”, the horizontal and vertical sizes of which coincide with the dimensions of the electronic “window” and correspond in time units to the geometric dimensions of the “window” of opacity.

Let the sizes of the 3-4 target be (L × H) in mm, and the dimensions of the “window” of opacity - (l × h) in the same units (see fig.3b). Suppose that the area of the “window” of opacity occupies 1/9 of the area of the entire photo target. If the image visible from the monitor screen has dimensions (L ₁ × H ₁ ), and the dimensions of the electronic “frame” and the “window” area are (a × b) in mm, as shown in Fig. 3a), then we have the ratio:

On the other hand, for a camera working in the broadcast standard, the dimensions of the “frame” and “window” in units of time are: a = 52/3 = 17.3 μs, b = 288 × 64/3 = 6144 μs.

Depending on the geometric shape of the controlled object with excessive illumination and / or brightness, other adequate geometric dimensions of the “window” of opacity and the time parameters of the “frame” and “window” are possible.

For the photodetector section 3-1, the slope (S ₁ ) of the “light-signal” conversion (see FIG. 4) is equal to:

where U _max - the maximum voltage of the linear section of the transformation "light - signal";

E _max - the illumination at which the saturation by carriers of potential targets of the photographic target 3-1 occurs.

The steepness of the "light - signal" conversion section 3-4 (S ₂ ) is:

where U _max - the maximum voltage of the linear section of the transformation "light - signal";

E ₂ - illumination at which the saturation by carriers of potential 3-4 target wells occurs.

Obviously, E ₂ <E _max , therefore, S ₁ <S ₂ .

The control pulse generator 4 is designed to scan in the CCD matrix 3 and generate service pulses for the signal processor 4. The VK 4-1 included in it can be made in the form of a large integrated circuit (LSI), for example, Sony CXD2463R microcircuit [3] . PU 4-2, which serves to convert the levels of logical signals VK 4-1 in the signal levels necessary for the operation of the matrix 3 of the CCD, can be implemented in the form of a second LSI necessary set.

The signal processor 5 is designed for two-channel amplification and processing of image signals from the outputs of the CCD; performing the AGC function for each channel; the formation of the first and second information outputs of composite video signals; formation of control signals at the first and second control outputs for the two-channel ARVN circuit. The signal processor 5 can be made in the form of one LSI or two CXA1310AQ microcircuits from Sony [4].

Note that in Fig. 1, within the signal processor 5, dashed lines show two electrical connections: from the output of the control signal of the video amplifier 5-1 to the first control output of the unit 5 and, accordingly, from the output of the control signal of the video amplifier 5-2 to the second control output of the unit 5. This is determined by the fact that the generated control signals are the result of detection of image signals, respectively, of the first and second channels, and the video signal detectors themselves can be either integrated into video amplifier microcircuits, They moved out of the overall chip signal processor.

Shaper 6, as in the prototype, using the input synchronization signals of horizontal and frame frequencies, generates electrical signals "frame" and "window". It is assumed that the "thickness" of the electronic "frame" is (1 ... 2) of the horizontal expansion element and, accordingly, (1 ... 2) vertical lines, therefore, for simplicity, the coincidence of their geometric dimensions and the corresponding time parameters is accepted.

The switch-mixer 7, as in the prototype, is designed to form a composite composite video signal. Bright and bright details of the scene observed by the camera are transmitted in it within the raster “window”. Within the remaining area of the frame, dark and / or low-lit scene details are transmitted.

The camera (see figure 1) works as follows.

The electronic “frame” signal, mixed into the camera’s video output signal, helps the operator to make the necessary recording of a scene image with high illumination and / or brightness using the combined image observed from the screen of the video monitor.

Suppose that the placement of the camera allows you to orient it so that highly illuminated and / or bright objects are perceived in a controlled image limited by an electronic “frame”, for example, in the central part of its viewing angle (see Fig. 3a).

The technological mask, applied to target 3-4, provides for it a “window” of opacity of the input light flux within the area defined by the electronic “frame”. Therefore, the average illumination value over the entire area of the photodetector section 3-4 will be determined by the level of illumination in that region located on the periphery of the “window”.

As a result, for the scene observed by the claimed television camera, the ARVN and AGC channel for section 3-1 and the ARVN and AGC channel for section 3-4 of photodetector 3 will establish different and optimal values of the current exposure and gain of video amplifiers 5-1 and 5-2 of signal processor 5, namely:

T _n1 <T _n2 ; K _y1 <K _y2 ,

where T _n1 , K _y1 - the duration of the current accumulation in section 3-1 and the gain of the video amplifier 5-1;

T _n2 , K _y2 - the duration of the current accumulation in sections 3-4 and the gain of the video amplifier 5-2.

It should be noted that the electronic shutter of section 3-1 is controlled from the third output of the control unit 4-2 via the feedback circuit from the output of the control unit 3-3 to the first control input of VK 4-1, and the electronic shutter of section 3-4 is controlled from the fourth output of the control unit 4-2 through the feedback circuit from the output of the BPZN 3-6 to the second control input of the VK 4-1.

Using the “window” of opacity allows to avoid light overload of the photodetector section 3-4 of the CCD matrix. But, in comparison with the prototype, due to the optimization of the shutter area (ΔS ₂ ) in BPS 3-6, an additional increase in the signal-to-noise ratio for dark and / or low-light scene details.

This factor serves as the basis for asserting the expansion of the dynamic range of the camera, estimated by the composite output video signal. If we turn to the light characteristics of the camera (see figure 4), then for the prototype the range of working illumination is (E _min1 ... E _max ), and for the claimed solution - (E _min2 ... E _max ), which is potentially wider than the first range by an order of magnitude.

In the proposed camera, the components of the combined image are generated in charge form on a crystal of a single CCD, and not on two crystals, as is implemented in the prototype. Therefore, the accuracy of formation and maintenance of the combined image in the inventive camera compared with the prototype will be obviously higher.

Currently, all blocks of the proposed solution have been mastered or can be mastered by domestic industry, therefore, the proposed invention should be considered as meeting the requirement for industrial applicability.

Information sources

1. Patent No. 2389151 of the Russian Federation. IPC H04N 5/225. A television camera for observation in conditions of complex illumination and / or complex brightness of objects / V.M.Smelkov // BI No. 13. - 2010.

2. Nikitin V.V., Tsytsulin A.K. Television in physical protection systems. SPb .: SPbGETU "LETI", 2001.

3. Sony CXA1310AQ chip. Single Chip Processing for CCD Camera. User manual in English, pp. 1-14.

4. Sony CXD2463R chip. Timing Controller for CCD Camera. Instructions for the user in English. S.1-12.

Claims (1)

A television camera for observation in difficult lighting conditions and / or complex brightness of objects, containing a sequentially located and optically coupled lens and a beam splitter, the first beam splitter output being optically coupled to the target plate of a charge-coupled device array (CCD matrix) with a horizontal transfer organization consisting of of the first photodetector section, the first horizontal register and the first block of charge-to-voltage conversion (BPS), sequentially connected by charge coupling, as well as a control generator pulses, consisting of a series-connected time controller (VK) and level converters (PU), a frame driver and a window, and a switch-mixer, the first and second outputs of the PU connected respectively to the control inputs of the first photodetector section and the first horizontal the register of the CCD matrix, and the third output of the CU to the electronic shutter of the first photodetector section, while the output of the first CPS sensor of the CCD is connected through the first information input of the signal processor to the information input the first video amplifier, whose control input, which is the control input of the signal processor, is connected to the second VK output, the first control input of which is connected to the first control output of the signal processor, whose first information output, which is the video output of the first video amplifier, is connected to the first information input mixer-switch, the output of which is the output of the "video" camera, the first and second control inputs of the switch-mixer are connected respectively to the output of the There’s a “window” and to the output of the “frame” signal of the shaper, the lowercase input and the frame synchronization input of which are connected respectively to the outputs of the lowercase and frame sync pulses of the VK, as well as the second video amplifier and the second photodetector section, the second horizontal register and the second CVD, connected in series with charge communication, moreover, the second photodetector section, the geometrical dimensions of which coincide with the geometrical dimensions of the first photodetector section, is optically connected to the second output of the beam splitter, and nological mask, providing for the input light flux a “window” of opacity, the spatial position of which and its geometric dimensions correspond to the temporary placement in the raster and parameters in units of time for the electronic “frame” and the electronic “window”, characterized in that the second photodetector section, the second a horizontal register and a second CVD are introduced into the CCD matrix crystal, and the second video amplifier is introduced into the signal processor, the control inputs of the second photodetector section and the second horizontally of the second register are connected respectively to the first and second outputs of the control unit, and the electronic shutter of the second photodetector section is connected to the fourth output of the control unit, the output of the second SEC sensor of the CCD through the second information input of the signal processor is connected to the information input of the second video amplifier, the control input of which is connected to the control input of the signal processor , the second control output of which is connected to the second control input of the VK, the output of the "video" of the second video amplifier, which is the second information output of the signal process sora connected to the second information input of the mixer-mixer, and the area ΔS _{1 of the} gate of the field-effect transistor collecting charge carriers in the first SPS is performed according to the criterion of the maximum control ability of the charge conversion, and the area ΔS _{2 of the} gate of a similar field-effect transistor in the second SPS is according to the criterion minimum introduction of the intrinsic noise into the image signal, while ΔS ₁ > ΔS ₂ .

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