Multi-region time-sharing exposure control method for single-chip image sensor and application of multi-region time-sharing exposure control method

Abstract

The invention discloses a multi-region time-sharing exposure control method for a single-chip image sensor and an application of the multi-region time-sharing exposure control method. The control method comprises the following steps of: logically partitioning a pixel array of a single-chip image sensor according to a shooting scene to obtain a plurality of exposure areas; according to the exposure time of different partitions, a pixel row decoder is controlled to expose the area needing to be exposed; after exposure is completed, the column reading circuit is controlled to read out, and exposure images of all the partitions at different moments and different exposure times are obtained. The method is used in the star guiding process. According to the method, multi-region time-sharing exposure of the single image sensor is realized, and meanwhile, the multi-region time-sharing exposure is applied to the astronomical field, so that a guided star image is acquired and a target image is shot on the same image sensor, the error is smaller when the guide star deviation is calculated, and more accurate guide star correction can be completed. The complex process problem of adjusting the guide star sensor and the main sensor to be in the same plane and the guide star calculation error caused by the adjustment error are avoided.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of image sensor control, and particularly relates to a single-chip image sensor multi-region time-sharing exposure control method and application. BACKGROUND

[0002] Astronomical observation and photography require long-time exposure of celestial bodies. In order to ensure the stability of the target during exposure, the telescope and imaging system need to track the target. The tracking system of the telescope located on the ground will have tracking errors caused by mechanical processing errors, polar axis deviation, atmospheric refraction, system stiffness, wind pressure and other problems. On a space telescope, the target will deviate due to microgravity, solar radiation pressure, satellite platform residual angular velocity and other reasons. In order to ensure that the starlight energy in the long-exposure photo is highly concentrated within the imaging limit diameter of the optical system (diffraction limit), whether on the ground or in space, the tracking process needs real-time closed-loop feedback control. By tracking and correcting the deviation of one or more bright stars near the target to be photographed, it is called "guide star" in astronomical observation. These stars tracked in the guide star process are called "guided stars". The telescope used for imaging the long-exposure target is called "primary mirror". The imaging time of the guided star is much shorter than the exposure time of the target photographed by the primary mirror. The former exposure time is in milliseconds, and the latter is in minutes.

[0003] Traditional guide star methods all need independent focal plane detectors to cooperate to realize the imaging of the guided star. The common imaging method of the guided star is as follows: 1. Guide star mirror guiding: the guide star focal plane detector is connected to an independent guide star telescope, which is fixedly connected to the primary mirror by mechanical means. However, since the aperture and focal length of the guide star mirror are smaller than those of the primary mirror, the error on the guide star mirror is smaller than that on the primary mirror, and the guide star sensitivity is small under the same center finding algorithm. In addition, due to the stiffness problem of mechanical connection, long-term tracking will deviate from the focal plane of the primary mirror.

[0004] 2. Off-axis guiding: the guided star is imaged on the guide star focal plane detector through a reflecting mirror raised to the edge of the primary mirror light path. However, this method can only find the guided star in a narrow ring area at the edge of the target photographed by the primary mirror. In addition, this guiding method cannot be used for optical systems with short flange distance. Large astronomical observatories and large-field space telescopes usually fix the guide star focal plane detector on the side of the primary mirror focal plane detector, which can solve the mechanical stiffness problem, but the range of the guided star is further limited.

[0005] 3. On-axis guiding: the guided star is imaged by a 45-degree beam splitter inserted in the light path of the primary mirror in the near-infrared band. However, due to the low quantum efficiency of silicon-based focal plane detectors in the infrared band, the signal-to-noise ratio of the guided star with the same brightness is slightly lower. In addition, due to the further increase of the distance from the full-size 45-degree beam splitter to the primary mirror detector, it is more difficult to use the short flange distance telescope; the beam splitter may introduce ghosting and other imaging defects.

[0006] Traditional image sensor driving timing can only control the simultaneous exposure of one or more regions, and cannot perform time-division exposure of different regions in the time domain. Therefore, it is impossible to simultaneously handle the short exposure of the guided satellite and the long exposure of the target image. To overcome the shortcomings of existing guiding systems, this invention proposes a multi-region time-division exposure control method for a single image sensor. By performing multi-region time-division exposure control on a single image sensor, a single image sensor can handle both the short exposure of the guided satellite and the long exposure of the target image, achieving on-chip guiding. Summary of the Invention

[0007] The purpose of this invention is to propose a multi-region time-division exposure control method for a single-chip image sensor to address the shortcomings of existing technologies, and to apply this method to the satellite guiding process, thereby achieving on-chip satellite guiding while improving guiding accuracy and simplifying the guiding equipment.

[0008] The control method described in this invention specifically involves: logically partitioning the pixel array of a single image sensor according to the shooting scene to create multiple exposure areas; controlling the pixel row decoder to expose the areas to be exposed according to the exposure time of different partitions; and controlling the column readout circuit to read out the images at different times and exposure times of each partition after the exposure is completed.

[0009] Furthermore, the host computer reads the exposure time, exposure duration, and coordinates of each zone; after the image sensor is powered on and zeroed, the host computer controls the image sensor to expose in each zone according to the zone exposure time and exposure duration; the multi-zone time-sharing exposure process is as follows: according to the zone exposure time, the host computer controls the image sensor to start exposing in the corresponding zone according to the set exposure parameters and exposure duration; when the zone at the previous moment has not yet reached the exposure duration, and the zone at the next moment needs to start exposure, the host computer controls the pixel row decoder to expose the pixel row corresponding to the zone that needs to start exposure; after the exposure is completed, the host computer sends instructions to the pixel area of ​​each exposure zone of the row decoder, and the instruction column readout circuit reads them out to obtain the exposure images of each zone at different times and exposure times.

[0010] Furthermore, before the exposure begins, the host computer sends a command to the pixel row decoder to select all pixels in the desired exposure zone and clear them to zero.

[0011] Preferably, control commands are sent to the pixel row decoder and column readout circuit via an FPGA and SoC processor. The image sensor is a CMOS image sensor.

[0012] On the other hand, the above control method can be applied to an on-chip guiding method, specifically: An image sensor is mounted on the focal plane of the main camera telescope, and multiple exposure areas are divided according to the main target and the guided star; the pixel row decoder is controlled to perform long exposures on the target area and short exposures on the guided star area; after exposure, the column readout circuit is controlled to read out the images, obtaining exposure images of each zone at different times and with different exposure times. The short exposure images are used to correct the pointing deviation of the main camera telescope, and mechanical control commands are output to adjust the pointing of the main camera telescope's support.

[0013] The control method described in this invention solves the problem of multi-region time-sharing exposure, which is impossible in traditional technologies. By applying multi-region time-sharing exposure to the astronomical field, it enables the acquisition of images of the guided star and the target image on the same image sensor, resulting in smaller errors when calculating guide star deviation and more accurate guide star correction. Both the guide star and the main camera are implemented through a single logical partition of the image sensor, eliminating the need for additional tracking mechanical axis calibration before guiding the star. A large image field angle starscape photo can be obtained by short exposure of the entire area of ​​the main sensor. The telescope's focal length, pixel size, and image field rotation direction can be directly obtained by analyzing the star catalog of this photo, completing the conversion of the guided star's position deviation on the sensor into the support movement command. This differs from traditional small-format guide stars sensors, which require multiple single-step attempts before startup to calculate the rotation vector. It eliminates the complex process of adjusting the guide star sensor and the main sensor to be on the same plane, and the guide star calculation errors introduced by adjustment errors.

[0014] Meanwhile, compared to traditional solutions that require an external guide mirror and another sensor to provide corrective images, the control method described in this invention only requires one image sensor to achieve precise tracking of celestial bodies, eliminating the need for additional guide mirrors or image acquisition equipment, thus simplifying the complexity of the system.

[0015] This solves the problem of guidance calculation errors caused by asynchronous deformation due to the structural stiffness of the connection between the guide mirror and the main mirror in traditional guidance methods that use external guide mirrors.

[0016] This solution addresses the shortcomings of traditional off-axis guiding methods, which require an additional off-axis guiding device. This device itself demands sophisticated manufacturing and assembly, and the off-axis guiding sensor and the sensor used to capture the target image are not on the same plane. The tilt of the guiding sensor introduces additional guiding calculation errors. Furthermore, if the mirrors used in off-axis guiding intrude too much into the optical path, they can obstruct the main sensor. Additionally, the off-axis guiding device occupies a section of the telescope between the last mirror and the sensor. With our solution, this section can be used for other scientific instruments, enabling more scientific tasks, or by reducing the distance between the last mirror and the sensor, greater freedom in the optical lens design regarding the distance between the lens elements and the focal plane.

[0017] Furthermore, it allows for smaller costs and dimensions, providing technical support for the development of large-format astronomical cameras with integrated guiding systems. In addition, it significantly reduces system weight, satellite size, and launch costs in small space telescopes and CubeSats. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of pixel coordinates in the invention; Figure 2 A schematic diagram of the coordinates of the region of interest (ROI); Figure 3 This is a diagram illustrating the overlap of exposure times; Figure 4 This is a schematic diagram of coordinates for multiple regions; Figure 5 This is a schematic diagram of the guiding regions for two guided stars in an application example; Figure 6 The images show the guiding effect; the left image shows the result after guiding, and the right image shows the result before guiding. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings.

[0020] For ease of explanation, this embodiment assumes that the number of pixel columns of the image sensor is 1. The number of columns and rows is Rows, using the column where the pixel is located as the row. Coordinates, the row they are in Coordinates, establish as follows Figure 1 The rectangular coordinate system shown has the pixel coordinates of the upper left corner of the sensor as follows: The bottom right pixel coordinates are .

[0021] When using a single image sensor, existing methods include two exposure modes: region of interest (ROI) exposure and full-area exposure.

[0022] Full-area exposure specifically refers to the user-specified top-left corner vertex. The bottom right corner is The duration of the area is After the exposure, the user can obtain an image with a size of [size missing]. Exposure duration is The photo.

[0023] The exposure of the Region of Interest (ROI) is specifically defined as: the top-left vertex specified by the user. The bottom-right vertex is The rectangular region takes a duration of The exposure, among which and , It can be modified according to the user's actual needs. After the exposure is complete, the user will receive an image with a size of [size missing]. Exposure duration is The photo. The exposed area is as follows: Figure 2 As shown.

[0024] Multiple ROI regions can also be exposed simultaneously, accelerating the image sensor's readout rate and reducing power consumption. After exposure, the user can obtain multiple ROI regions, each with the same exposure time. However, if the exposure time periods of these regions partially overlap... Figure 3 As shown, this method cannot be used for regional and time-segmented exposure.

[0025] A method for multi-region time-division exposure control of a single-chip image sensor, specifically: The scene that the image sensor needs to capture Each object is numbered, starting from... To begin, the last object is numbered And divide the space according to the size of each object, such as... Figure 4 As shown, numbered The coordinates of the top left corner of the object's image region are The coordinates of the lower right corner are And so on: the coordinates of the top-left corner of the image region for object number 0 are... The coordinates of the lower right corner are The top-left corner coordinates of the image region for object number 1 are... The coordinates of the lower right corner are Number is The coordinates of the top left corner of the object's image region are The coordinates of the lower right corner are .

[0026] Expose n image regions as needed, for any image region At the start of the exposure Image regions are read out using FPGA and SoC processors. The pixel row To achieve the initial exposure area The purpose; then exposure begins on the image sensor for charge integration, until... At any time, pixel rows are controlled via FPGA and SoC processor. arrive Data is read out to obtain the image region. Exposure duration The image.

[0027] During single-area exposure, the pixel rows in other areas are not read out, and charge integration can continue. Therefore, these exposure areas do not affect each other and can be exposed independently.

[0028] The host computer (FPGA and SoC processor) reads the exposure time, exposure duration, and coordinates (lower right and upper left corner coordinates) of each zone. Before exposure begins, the host computer sends a command to the pixel row decoder to select all pixels in the desired exposure zone and clear them. After the image sensor is powered on and cleared, the host computer controls the image sensor to expose in each zone according to the zone exposure time and exposure duration. The multi-zone time-sharing exposure process is as follows: According to the zone exposure time, the host computer (FPGA and SoC processor) controls the image sensor to start exposing in the corresponding zone according to the set exposure parameters and exposure duration. When the zone at the previous moment has not reached the exposure duration and the zone at the next moment needs to start exposure, the host computer (FPGA and SoC processor) controls the pixel row decoder to expose the pixel row corresponding to the zone that needs to start exposure. After exposure is completed, the host computer sends a command to the pixel area of ​​each exposure zone in the row decoder and reads it out by the command line readout circuit to obtain the exposure images of each zone at different times and exposure times.

[0029] Application examples This application example uses the Changguang Chenxin GSense5130 CIS image sensor to illustrate the process of applying the above-mentioned multi-region time-division control method of a single image sensor to on-chip satellite guidance. In this example, two guided stars, G0 and G1, are selected, and two independent guiding imaging areas are used for each. In this example, exposure time is measured in rows: the exposure time of the primary star (long exposure time) is TL rows, and the exposure time of the guided star (short exposure time) is TS rows. TS is much smaller than the long exposure time TL and much larger than the total number of operable pixel rows N of the image sensor (N << TS << TL). In actual use, one or more guided star imaging areas can be selected. Within each area, multiple guided stars can be placed horizontally within the same guided star area by calculating the position of the guided star and rotating the image sensor.

[0030] like Figure 5 As shown, an imaging region is selected for each guided star. The imaging region for guided star G0 starts at row YsG0 pixels and ends at row YeG0 pixels. The imaging region for guided star G1 starts at row YsG1 pixels and ends at row YeG1 pixels.

[0031] In the following image sensor capture and guiding process, Y represents the current selected path of the image sensor, and the image sensor has a total of N rows of operable pixels: Step 1. Long exposure begins; zeroing the charge on the image sensor. The image sensor selects the first row of pixels (Y == 0) and performs a charge zeroing operation on that row. Exposure begins for that row, and time T, calculated in rows, is simultaneously started. The image sensor performs zeroing row by row, incrementing Y by 1 at each step (Y = Y + 1). Zeroing ends when Y reaches the maximum pixel row N-1 of the image sensor.

[0032] Step 2. After waiting for TS - (YeG1 + YeG0 - YsG1 - YsG0 + 2) rows, select the YsG0 row of pixels on the image sensor (Y == YsG0) and perform charge readout. Since image sensor charge readout is an irreversible process, the charge of that row of pixels is cleared to zero after readout, and the next frame exposure for that guiding region begins immediately. Increase the row selection line by line and repeat the charge readout operation until the row selection reaches the last row of pixels in the guided G0 imaging region (Y == YeG0). This yields a guiding image of the guided G0 imaging region with an exposure time close to TS.

[0033] Step 3. After waiting for the TS line time, select the YsG1 row of pixels on the image sensor (Y == YsG1) and perform charge readout. Increase the row selection line by line and repeat the charge readout operation until the row selection reaches the last row of pixels in the guided star G1 imaging region (Y == YeG1). Obtain a guiding image of the guided star G1 guiding region with an exposure time close to the TS time.

[0034] Step 4. Readout of Long Exposure. Select row 0 (Y==0) on the image sensor and perform a readout operation. Reset the counter T and restart the long exposure timing. Increment Y row by row (Y=Y+1) and perform readout operations until Y reaches the maximum row (Y==N-1). Completing this step yields an image of N rows, which is the target photograph for the long exposure. In the photograph, the regions of rows YsG0~YeG0 and YsG1~YeG1 have no effective signal due to repeated guide star readout, while other regions experience photoelectron accumulation over a time of TL rows.

[0035] Repeat steps 2 through 4. Each time step 2 is repeated, the TS exposure time can be changed, and the following check should be performed: When the accumulated time T reaches the following condition: TL – T <= TS, stop repeating and execute step 4. In actual operation, the exposure time of G0 and G1 in the guiding region needs to be increased by the time difference of the entire region readout in addition to TS. However, since TS is usually much larger than N, the exposure time of G0 and G1 is close to TS.

[0036] To demonstrate the effectiveness of the above methods in the star guidance process, the following are provided: Figure 6 The image shown is a comparison of the actual guiding effect before and after. Figure 6 As can be seen, the method described in this invention can achieve good guiding effect.

[0037] The above content and structure describe the basic principles, main features, and advantages of the product of this invention, which should be understood by those skilled in the art. The examples and descriptions above are merely illustrative of the principles of this invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for multi-region time-division exposure control of a single-chip image sensor, characterized in that: Specifically, the pixel array of a single image sensor is logically partitioned according to the shooting scene to create multiple exposure areas; the pixel row decoder is controlled to expose the areas to be exposed according to the exposure time of different partitions; after exposure is completed, the column readout circuit is controlled to read out the images at different times and exposure times of each partition.

2. The multi-region time-division exposure control method for a single-chip image sensor as described in claim 1, characterized in that: The host computer reads the exposure time, exposure duration, and coordinates of each zone. After the image sensor is powered on and zeroed, the host computer controls the image sensor to expose in each zone according to the zone exposure time and exposure duration. The multi-zone time-sharing exposure process is as follows: According to the zone exposure time, the host computer controls the image sensor to start exposing in the corresponding zone according to the set exposure parameters and exposure duration. When the zone at the previous moment has not reached the exposure duration and the zone at the next moment needs to start exposure, the host computer controls the pixel row decoder to expose the pixel row corresponding to the zone that needs to start exposure. After the exposure is completed, the host computer sends instructions to the pixel area of ​​each exposure zone of the row decoder and the instruction column readout circuit reads them out to obtain the exposure images of each zone at different times and exposure times.

3. The multi-region time-division exposure control method for a single-chip image sensor as described in claim 1, characterized in that: Before the exposure begins, the host computer sends a command to the pixel row decoder to select all pixels in the desired exposure zone and clear them to zero.

4. The multi-region time-division exposure control method for a single-chip image sensor as described in claim 1, characterized in that: The FPGA and SoC processor send control commands to the pixel row decoder and column readout circuit.

5. The multi-region time-division exposure control method for a single-chip image sensor as described in claim 1, characterized in that: The image sensor mentioned is a CMOS image sensor.

6. The on-chip guiding method employing the control method as described in claim 1, characterized in that: Specifically, the image sensor is mounted on the focal plane of the main camera telescope, and multiple exposure areas are divided according to the main shooting target and the guided star; the pixel row decoder is controlled to perform long exposure on the shooting target area and short exposure on the guided star area; after the exposure is completed, the column readout circuit is controlled to read out the images at different times and exposure times of each zone; the short exposure images are used to correct the deviation of the main camera telescope's pointing, and mechanical control commands are output to adjust the pointing of the main camera telescope's support.

Images