A method for dynamic dimming of CMOS image sensor for star sensor

Abstract

The present invention relates to a method for dynamic dimming of a CMOS image sensor for a star sensor, comprising: obtaining the integration time of the CMOS image sensor in real time and determining whether the integration time has changed. If the integration time has increased, the row address of the readout phase in the imaging timing of the CMOS image sensor is maintained unchanged, and the reset phase of the current frame image is changed from a single-address reset timing to a dual-address reset timing. The dual-address reset timing includes reset phase row addresses corresponding to the integration time change before and after the integration time change, and the reset phases of subsequent frames after the current frame image all use the reset phase row addresses corresponding to the integration time change until the next integration time change. The present invention can eliminate the occurrence of incomplete frames due to integration time changes, and does not require image caching during the dynamic dimming process, thereby preventing image loss. This ensures the continuity of valid position information output by the star sensor during large-angle motion.

Description

Technical Field

[0001] The present invention relates to the technical field of photoelectric imaging, and in particular to a method for dynamic light adjustment of a CMOS image sensor used in a star sensor. Background Art

[0002] Star sensors are high-precision space attitude measurement devices that use stars as a reference system and the starry sky as their working object. By detecting and calculating stars at different locations on the celestial sphere, they provide accurate spatial orientation and reference for satellites, spacecraft, and other spacecraft. Like inertial gyroscopes, they also possess autonomous navigation capabilities, making them of great application value. The operating principle of a star sensor is as follows: a CMOS image sensor captures an image of the starry sky within its current field of view. This image undergoes signal processing to extract the brightness signals of the stars in the observation field. A star map recognition algorithm then finds corresponding pairs of observed stars in a navigation star library. These matching pairs are used to calculate the star sensor's three-axis attitude.

[0003] Currently, satellites, space stations and other spacecraft all have the ability to maneuver on orbit. When maneuvering, spacecraft often move at very high speeds and have large maneuvering angular velocities. Therefore, effective and rapid attitude output at large angular velocities is an important technical indicator of star sensors. The most effective way to improve the dynamic performance of star sensors is to adjust the integration time to reduce the trailing of stars in the star map. Under different angular velocity conditions, star sensors need to have the ability to dynamically adjust the integration time, and while dynamically adjusting the integration time, it is necessary to ensure both the rapidity and continuity of the output of effective attitude information. Currently, in order to ensure uninterrupted imaging during dynamic dimming, the following two methods are used:

[0004] One method is to cache the current frame image data when the CMOS image sensor imaging module receives the integration time adjustment signal, then interrupt the exposure pipeline and re-expose it. The disadvantage of this method is that the exposure pipeline will be interrupted and re-exposure is required. It takes at least two frames of image time to obtain the image data under the new integration time, so at least two frames of image will be lost. Another method is to save idle time by changing the blanking time of each row, and then use the idle time to adjust the exposure pipeline to achieve uninterrupted exposure. However, this method will cause the timing of the row-field synchronization to change with the change of the integration time. This requires caching an entire frame of image to be compatible with other modules in the software, and the blanking time needs to be greater than or equal to the maximum integration time, that is, the imaging time of an entire frame. Therefore, this method also has the possibility of losing a frame of image data.

[0005] Therefore, in order to solve the above problems, it is urgent to propose an exposure method to achieve continuous dynamic dimming and solve the problem of discontinuous output of effective pose information of star sensors during large-angle motion. Summary of the Invention

[0006] To address the above problems, the present invention provides a method for dynamic dimming of a CMOS image sensor for a star sensor. This method implements continuous dynamic dimming based on a dual-address reset exposure method, effectively solving the problem of discontinuous output of valid pose information during large-angle motion of the star sensor.

[0007] The present invention adopts the following technical solutions:

[0008] A method for dynamic dimming of a CMOS image sensor for a star sensor comprises the following steps:

[0009] Step 1: Obtain the integration time of the CMOS image sensor in real time;

[0010] Step 2: Determine whether the integration time has changed. If the integration time has increased, execute step 3. If the integration time has decreased or remained unchanged, maintain the single-address reset timing in the reset phase of the CMOS image sensor imaging timing and the row address in the readout phase unchanged. When the integration time decreases, the single-address reset timing is the reset phase row address corresponding to the change in the integration time.

[0011] Step 3: Keep the row address of the readout phase in the imaging timing of the CMOS image sensor unchanged, and change the reset phase of the current frame image from a single-address reset timing to a dual-address reset timing. The dual-address reset timing includes the reset phase row addresses corresponding to before and after the integration time is changed, and the reset phases of other frame images after the current frame image all use the reset phase row addresses corresponding to the integration time change until the next integration time change.

[0012] The present invention has the beneficial effects of: the method for dynamic dimming of a CMOS image sensor for a star sensor proposed in the present invention determines whether to adopt a dual-address reset sequence in the reset phase of the CMOS image sensor imaging sequence based on whether the integration time increases. When the integration time increases, the reset phase in the imaging sequence of the CMOS image sensor is divided into two, performing two row address resets, while the row address in the readout phase remains unchanged. Therefore, the occurrence of incomplete frames due to changes in the integration time can be eliminated. In addition, the exposure method based on the dual-address reset realizes that the dynamic dimming process does not require image caching and does not result in image loss, thereby ensuring the continuity of valid position information output by the star sensor during large-angle motion. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of the imaging process of the Mth row of CMOS image sensors;

[0014] Figure 2 This is the frame timing diagram for reading the first row of image data;

[0015] Figure 3 This is a flow chart of a method for dynamic dimming of a CMOS image sensor for a star sensor according to the present invention;

[0016] Figure 4 This is the imaging timing diagram after the integration time is changed;

[0017] Figure 5 The row addresses in the readout phase and the reset phase of the first and second frame images when the integration time is 2 line periods;

[0018] Figure 6 The row addresses in the readout phase and the reset phase of the first and second frame images when the integration time is 4 line periods;

[0019] Figure 7 These are the readout phase row address and reset phase row address of the first frame image and the second frame image when the integration time changes from 2 line cycles to 4 line cycles. DETAILED DESCRIPTION

[0020] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments.

[0021] In the star sensor, the imaging mode in the CMOS image sensor is to expose row by row, and the pixel value of each row is read out after the exposure is completed. The exposure principle is that when imaging the Mth row, the row is first reset, the sensor drive pin RST is changed to low, and the row register ROW is set to the row number of this row, so as to realize the zeroing of the charge in the photosensitive area capacitor. As the light is irradiated, the charge will continue to accumulate on the capacitor. After a certain period of time (integration time), the accumulated charge is converted into a voltage signal, that is, the pixel value, and then a read operation is performed. The read operation is to change the sensor drive pin RST to high, and the row register ROW is set to the row number of this row. The imaging process of the Mth row is as follows Figure 1 As shown in the figure, the time difference between the time pointer of the read operation and the time pointer of the reset operation is the integration time. Therefore, if the integration time remains unchanged, the time difference between them is fixed; as the integration time decreases, the time difference between them decreases; as the integration time increases, the time difference between them increases.

[0022] The following describes the imaging process of the entire frame. For a fixed integration time, the operation timing of each frame image is the same. Each row cycle is divided into a reset phase and a read phase. In the reset phase, a certain row is reset, and in the read phase, a certain row is read. Taking the reading of the first row image data as an example, the frame timing diagram is as follows Figure 2As shown in the diagram, the readout time pointer executes one cycle according to the timing diagram to generate one frame of image data. This repetition generates multiple frames of continuous image data. When the readout pointer completes its first clockwise cycle, the first line of image data is output. As long as the integration time remains constant, the time difference between the readout time pointer and the reset time pointer remains constant.

[0023] Adjusting the integration time alters the current frame timing pipeline, resulting in incomplete frames. Therefore, the present invention proposes a method for dynamic dimming of a CMOS image sensor for a star sensor. This method, based on a dual-address reset exposure method, achieves continuous dynamic dimming of the CMOS image sensor, eliminating incomplete frames and thus resolving the issue of discontinuous output of valid pose information during large-angle motion of the star sensor.

[0024] The current CMOS image sensor timing reset stage is a single address reset, that is, in the reset stage, the row address remains unchanged. The specific method of dynamic dimming of the CMOS image sensor based on dual address reset proposed by the present invention is as follows: Figure 3 As shown, the following steps are included:

[0025] Step 1: Obtain the integration time of the CMOS image sensor in real time;

[0026] Step 2: By comparing the real-time acquired integration time with the integration time at the previous moment, it is determined whether the integration time has changed. If the integration time has increased, step 3 is executed, that is, the reset phase in the imaging timing is divided into two, and the row address is reset twice. If the integration time decreases or remains unchanged, the reset phase in the imaging timing of the CMOS image sensor adopts a single-address reset timing and the row address in the readout phase remains unchanged. When the integration time decreases, the single-address reset timing adopted in the reset phase is the reset phase row address corresponding to the change in the integration time.

[0027] Step 3: Keep the row address of the readout phase in the imaging timing of the CMOS image sensor unchanged, and change the reset phase of the current frame image from a single-address reset timing to a dual-address reset timing. The dual-address reset timing includes the reset phase row addresses corresponding to before and after the integration time is changed, and the reset phases of other frame images after the current frame image all use the reset phase row addresses corresponding to the integration time change until the next integration time change.

[0028] Furthermore, when the integration time increases, the integration time change flag, frame_expose_change, is set high. When the integration time decreases or remains unchanged, the integration time change flag, frame_expose_change, is set low. When frame_expose_change is high, the reset phase of the current frame image uses a dual-address reset sequence. When frame_expose_change is low, the reset phase of the current frame image uses a single-address reset sequence.

[0029] Compared with the single address reset timing, the dual address reset timing is different in that only the TX1 signal is different, and the other signals remain unchanged. Figure 4 As shown, Figure 4 Reset (AddressN) and Reset (AddressQ) represent the reset addresses under different integration times, and Read (AddressM) represents the row address in the readout phase.

[0030] Assuming that there are 6 lines of image data in a frame of image, the following only takes this as an example to illustrate the dynamic dimming method of the present invention.

[0031] When the integration time is 2 line cycles, when the image data of the first line is read, the image data of the third line is reset. When the image data of the second line is read, the image data of the fourth line is reset. Similarly, the read address (i.e., the row address in the readout phase) and reset address of the first and second frame images are as follows: Figure 5 shown.

[0032] When the integration time is 4 line cycles, when reading the image data of the first line, the image data of the fifth line is reset. When reading the image data of the second line, the image data of the sixth line is reset. Similarly, the read address and reset address of the first frame image and the second frame image are as follows: Figure 6 shown.

[0033] When the integration time is changed for imaging, the integration time is changed from 2 line cycles to 4 line cycles. At this time, a dual-address reset is performed on the first frame image, and the other frame images use a single-address reset sequence. In the dual-address reset, the row address of the readout phase remains unchanged, and the address of the reset phase includes the reset phase row address when the integration time is 4 and 2. The readout phase row address and reset phase row address of the first frame image and the second frame image after the integration time is changed are as follows: Figure 7 shown.

[0034] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned 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.

[0035] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for dynamic dimming of a CMOS image sensor for a star sensor, characterized in that: The following steps are involved: Step 1: Acquire the integration time of the CMOS image sensor in real time, where the integration time is the time difference between the time pointer of the read operation and the time pointer of the reset operation; Step 2: Determine whether the integration time has changed. If the integration time has increased, execute step 3. If the integration time has decreased or remained unchanged, maintain the single-address reset timing in the reset phase of the CMOS image sensor imaging timing and the row address in the readout phase unchanged. When the integration time decreases, the single-address reset timing is the reset phase row address corresponding to the change in the integration time. Step 3: Keep the row address of the readout phase in the imaging timing of the CMOS image sensor unchanged, and change the reset phase of the current frame image from a single-address reset timing to a dual-address reset timing. The dual-address reset timing includes the reset phase row addresses corresponding to before and after the integration time is changed, and the reset phases of other frame images after the current frame image all use the reset phase row addresses corresponding to the integration time change until the next integration time change.

2. The method for dynamic dimming of a CMOS image sensor for a star sensor according to claim 1, wherein: When the integration time increases, the integration time change flag frame_expose_change is set to a high level; when the integration time decreases or remains unchanged, the integration time change flag frame_expose_change is set to a low level.

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