An automatic dimming method for an imaging system based on a CMOS image sensor

Abstract

This invention relates to an automatic dimming method for an imaging system based on a CMOS image sensor, comprising the following steps: A DSP receives image information from an FPGA, and calculates the image grayscale histogram based on the image information, calculates the integration time and gain value, and outputs a dimming command to the FPGA; The FPGA uses the dimming command as an address to look up the final integration time and gain value in its on-chip ROM and sends it to the CMOS image sensor; When the ADC gain value changes, the ADC gain setting time is increased to 20ms, shortening the interval time of the frame request signal, thereby reducing the frame blanking time of the image signal output by the CMOS image sensor; After the shortened frame blanking time reaches 20ms, the interval time of the frame request signal is adjusted back to the original interval time. This automatic dimming method effectively solves the problem of continuous image flickering, making the automatic dimming process of the imaging system continuous and gradual.

Description

Technical Field

[0001] This invention relates to the field of automatic dimming technology for optical imaging systems, and in particular to an automatic dimming method for imaging systems based on CMOS image sensors. Background Technology

[0002] The aiming scope is an optical imaging system based on a CMOS image sensor. It is a component for measuring the Earth's attitude during manned spacecraft observation. Astronauts can use the TV aiming scope to observe the Earth and determine the spacecraft's attitude within a certain range of accuracy. During the spacecraft's orbital operation, the optical principal axis of the aiming scope is parallel to the spacecraft's Zb axis, which points towards the Earth's center. The aiming scope provides images of the Earth as observed from the transport spacecraft and transmits these images to an integrated electronic display screen installed on the spacecraft via an instrument image interface. Astronauts can determine the spacecraft's pitch and roll attitude using the peripheral field of view images on the integrated electronic display screen, and determine the spacecraft's yaw attitude by comparing the direction of image movement in the central field of view on the integrated electronic display screen with the scale lines on the aiming scope, allowing for manual control of the spacecraft's attitude.

[0003] Since the brightness of the Earth's surface is not constant, the scope needs to have an automatic dimming function so that the target can be clearly displayed on the screen within the illumination range of 1lx to 110,000lx.

[0004] The CMV4000 CMOS image sensor is a low-noise, high-dynamic-range CMOS image sensor manufactured by CMOSIS. Specific parameters are shown in Table 1 and... Figure 1 As shown.

[0005] Table 1 Main parameters of CMV4000

[0006] Serial Number parameter index 1 Manufacturers AMS 2 Pixel size (H×V) 5.5μm×5.5μm 3 Effective number of pixels (H×V) 2048(H)×2048(V) 4 Pixel clock 96MHz 5 Frame rate (fps) 180 6 quantum efficiency 62%@550nm 7 Dynamic range 60dB@GlobalShuttermode 8 transient noise <![CDATA[13e - ]]> 9 Dark current <![CDATA[125e - / s]]> 10 Full well charge <![CDATA[13.5Ke - ]]> 11 Operating temperature -30℃～+70℃ 12 Storage temperature -30℃～+70℃

[0007] The block diagram of the dimming control circuit of the CMOS image sensor is as follows: Figure 2 As shown, the image information generated by the CMOS image sensor is converted into data by the FPGA and sent to the DSP. The DSP receives the image information from the FPGA, calculates the average gray value, and sends a dimming command to the CMOS image sensor for dimming as required. According to the usage requirements, the scope needs to achieve clear imaging within an illuminance range of 1x to 110000 lx and also needs to achieve continuous, gradual dimming. This requires adjusting the gain value of the CMOS image sensor during automatic dimming. However, in traditional CMOS image sensor-based imaging systems, if the ADC gain value changes during automatic dimming, the image is prone to continuous flickering, making continuous, gradual dimming impossible and severely affecting image quality. Summary of the Invention

[0008] To address the problem that traditional CMOS image sensor-based imaging systems often exhibit continuous image flickering during automatic dimming when the gain value changes, making continuous, gradual dimming impossible and severely impacting image quality, this invention provides an automatic dimming method for CMOS image sensor-based imaging systems.

[0009] The technical solution adopted in this invention is as follows:

[0010] An automatic dimming method for an imaging system based on a CMOS image sensor includes the following steps:

[0011] Step 1: The DSP receives image information from the FPGA, calculates the image grayscale histogram based on the image information, calculates the integration time and gain value, and outputs a dimming command to the FPGA based on the integration time and gain value. The process of calculating the image grayscale histogram and the integration time and gain value based on the image information is as follows:

[0012] Step 1.1: Sum the pixels in the image with a gray level greater than 40 to obtain the average gray value;

[0013] Step 1.2: Determine if the average gray value is less than 70. If so, first increase the integration time. When the integration time is increased to its maximum value and still cannot meet the imaging brightness requirements, increase the gain value until the imaging requirements are met. The DSP outputs the dimming command corresponding to the current integration time and the current gain value to the FPGA. If not, proceed to step 1.3.

[0014] Step 1.3: Determine if the average gray value is greater than 100. If so, first reduce the gain value. When the gain value is reduced to the minimum gain value and still cannot meet the imaging brightness requirements, then reduce the integration time until the imaging requirements are met. The DSP outputs the dimming command corresponding to the current integration time and the current gain value to the FPGA.

[0015] Step 2: The FPGA receives the dimming command sent by the DSP via the serial port, uses the dimming command as the address to look up the final integration time and gain value in the FPGA's on-chip ROM, and sends the final integration time and gain value to the CMOS image sensor. When the ADC gain value sent by the FPGA to the CMOS image sensor changes, the FPGA increases the ADC gain setting time of the CMOS image sensor to 20ms and shortens the interval time of the frame request signal. After the frame blanking time of the CMOS image sensor output image signal reaches 20ms, the interval time of the frame request signal is adjusted back to the original interval time.

[0016] The beneficial effects of this invention are:

[0017] (1) The automatic dimming method proposed in this invention is applicable to the automatic dimming process of the scope. It adopts the method of simultaneously adjusting the PGA gain, ADC gain and integration time, and is configured with 1160 dimming levels, so that the scope can clearly image within the illuminance range of 1x to 110000lx.

[0018] (2) The FPGA increases the ADC gain configuration time of the CMOS image sensor and shortens the interval time of the frame request signal, thereby reducing the frame blanking time of the CMOS image sensor output image signal and solving the problem of continuous image flickering when the ADC gain jumps during the automatic dimming process of the aiming scope.

[0019] (3) Through theoretical calculation and experimental calibration, the optimal combination of PGA gain, ADC gain and integration time is achieved, so that the scope can achieve continuous and gradual dimming and improve the imaging quality. Attached Figure Description

[0020] Figure 1 This is the spectral response diagram of the CMV4000 CMOS image sensor;

[0021] Figure 2 This is a block diagram of the dimming control circuit for a CMOS image sensor.

[0022] Figure 3 This is a flowchart illustrating an automatic dimming method for an imaging system based on a CMOS image sensor, as described in an embodiment of the present invention.

[0023] Figure 4 This is a flowchart of the FPGA's processing of dimming commands. Detailed Implementation

[0024] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and preferred embodiments.

[0025] The automatic dimming process of an imaging system based on a CMOS image sensor can be divided into two processes: 1) The DSP calculates the image grayscale and sends a dimming command to the FPGA via a serial port; 2) After receiving the dimming command, the FPGA determines the gain value and integration time by looking up a table and sends them to the CMOS image sensor.

[0026] like Figure 3 As shown, this embodiment of the invention provides an automatic dimming method for an imaging system based on a CMOS image sensor, comprising the following steps:

[0027] Step 1: The DSP receives the image information sent by the FPGA, and calculates the image grayscale histogram based on the image information, calculates the integration time and gain value, and outputs the dimming command to the FPGA based on the calculated integration time and gain value.

[0028] The specific process by which the DSP calculates the integral time and gain value based on the image information and statistically analyzes the image grayscale histogram is as follows:

[0029] Step 1.1: Sum the pixels in the image with a gray level greater than 40 to obtain the average gray value;

[0030] Step 1.2: Determine if the average gray value is less than 70. If so, first increase the integration time. When the integration time is increased to the maximum value (e.g., 33222μs±1μs), if the imaging brightness requirement is still not met, then increase the gain value until the imaging requirement is met. The DSP outputs the dimming command corresponding to the current integration time and the current gain value to the FPGA. If not, proceed to step 1.3.

[0031] Step 1.3: Determine if the average gray value is greater than 100. If so, first reduce the gain value. When the gain value is reduced to the minimum gain value, if it still cannot meet the imaging brightness requirements, then reduce the integration time (the minimum integration time is 5μs±1μs) until the imaging requirements are met. The DSP outputs the dimming command corresponding to the current integration time and the current gain value to the FPGA.

[0032] In this embodiment, the integration time adjustment range is from 5μs (±1μs) to 33222μs (±1μs). The gain is divided into PGA gain and ADC gain, with the PGA gain having four levels: 00, 01, 02, and 03.

[0033] Step 2: After receiving the dimming command from the DSP via the serial port, the FPGA uses the dimming command as an address to look up the final dimming parameters (integration time and gain value) in the FPGA's on-chip ROM. This final integration time and gain value are then sent to the CMOS image sensor. When the ADC gain value sent by the FPGA to the CMOS image sensor changes, the FPGA increases the ADC gain setting time of the CMOS image sensor to 20ms, shortening the interval of the frame request signal, thereby reducing the frame blanking time of the CMOS image sensor's output image signal. Once the frame blanking time of the CMOS image sensor's output image signal reaches 20ms, the interval of the frame request signal is adjusted back to its original interval.

[0034] Furthermore, such as Figure 4 As shown, the FPGA processes dimming commands as follows:

[0035] S1. Determine if the ADC gain value has changed. If yes, proceed to S2; otherwise, proceed to S9.

[0036] S2. Assign the value 0 to the counter variable cnt;

[0037] S3. Send the gain value to the CMOS image sensor;

[0038] S4. Determine if variable cnt is greater than 0x208d5. If yes, proceed to S5; otherwise, increment variable cnt by 1 and re-evaluate.

[0039] S5. Set the frame count variable cnt_req to 0;

[0040] S6. Send a frame request signal to the CMOS image sensor, and the period of the frame request signal is (t-2) ms;

[0041] S7. Determine if the variable cnt_req is greater than 9. If yes, proceed to S8; otherwise, increment the variable cnt_req by 1 and return to S6.

[0042] S8. Send a frame request signal to the CMOS image sensor, and the period of the frame request signal is tms;

[0043] S9. Send the gain value to the CMOS image sensor;

[0044] S10. Send a frame request signal to the CMOS image sensor, and the period of the frame request signal is tms.

[0045] CMOS image sensors are characterized by their light weight, low cost, and high dynamic range. In traditional CMOS image sensor-based imaging systems, during automatic dimming, changes in the ADC gain value can easily lead to continuous image flickering. This invention proposes an automatic dimming method based on CMOS image sensors. When the ADC gain value changes, the ADC gain setting time of the CMOS image sensor is increased to 20ms, shortening the interval of the frame request signal and thus reducing the frame blanking time of the CMOS image sensor's output image signal. After the shortened frame blanking time reaches 20ms, the interval of the frame request signal is adjusted back to its original interval. This automatic dimming method effectively solves the problem of continuous image flickering, making the automatic dimming process of the imaging system continuous and gradual.

[0046] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0047] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. An automatic light adjustment method of a CMOS image sensor-based imaging system, characterized by, The method comprises the following steps: Step 1: the DSP receives the image information sent by the FPGA, and calculates the integral time and the gain value according to the image information, and outputs the dimming instruction to the FPGA according to the integral time and the gain value, wherein the process of calculating the integral time and the gain value according to the image information is as follows: Step 1.1: the pixels with the gray level greater than 40 in the image are accumulated and summed to obtain the average gray value; Step 1.2: whether the average gray value is less than 70 is judged, if yes, the integral time is first increased, when the integral time is increased to the maximum integral time and still cannot meet the imaging brightness requirement, the gain value is then increased, until the imaging requirement is met, and the DSP outputs the dimming instruction corresponding to the current integral time and the current gain value to the FPGA; if not, step 1.3 is executed; Step 1.3: whether the average gray value is greater than 100 is judged, if yes, the gain value is first decreased, when the gain value is decreased to the minimum gain value and still cannot meet the imaging brightness requirement, the integral time is then decreased, until the imaging requirement is met, and the DSP outputs the dimming instruction corresponding to the current integral time and the current gain value to the FPGA; Step 2: the FPGA receives the dimming instruction sent by the DSP through the serial port, looks up the final integral time and the gain value in the FPGA internal ROM by taking the dimming instruction as the address, and sends the final integral time and the gain value to the CMOS image sensor, when the ADC gain value sent by the FPGA to the CMOS image sensor changes, the FPGA increases the ADC gain setting time of the CMOS image sensor to 20 ms, shortens the interval time of the frame request signal, and adjusts the interval time of the frame request signal to the original interval time after the frame blanking time of the image signal output by the CMOS image sensor reaches 20 ms; The processing process of the FPGA on the dimming instruction is as follows: S1, whether the ADC gain value changes is judged, if yes, S2 is entered; if not, S9 is entered; S2, the counter variable cnt is assigned to 0; S3, the gain value is sent to the CMOS image sensor; S4, whether the variable cnt is greater than 0x208d5 is judged, if yes, S5 is entered; if not, the variable cnt is increased by 1 and re-judged; S5, the frame counting variable cnt_req is assigned to 0; S6, the frame request signal is sent to the CMOS image sensor, and the period of the frame request signal is (t-2) ms; S7, whether the variable cnt_req is greater than 9 is judged, if yes, S8 is entered; if not, the variable cnt_req is increased by 1 and returned to S6; S8, the frame request signal is sent to the CMOS image sensor, and the period of the frame request signal is t ms; S9, the gain value is sent to the CMOS image sensor; S10, the frame request signal is sent to the CMOS image sensor, and the period of the frame request signal is t ms.

2. The automatic exposure method of a CMOS image sensor-based imaging system according to claim 1, wherein, The adjustment range of the integral time is 5 μs to 33222 μs.

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