A method for correcting parasitic light response of an ultra-high-speed double-frame transient image

Abstract

This invention relates to a parasitic light sensitivity correction method for CMOS image sensors, specifically a method for ultra-high-speed dual-frame transient imaging with CMOS image sensors. It addresses the technical problems of existing parasitic light sensitivity correction systems being highly complex or unsuitable for transient imaging where the light intensity of the imaging target changes rapidly. The method involves selecting an image sensor and an image intensifier, coupling them, controlling the timing of the acquisition of two exposure images, removing the background from both images, and then performing parasitic light sensitivity correction. By controlling the timing of the image sensor and image intensifier, the parasitic light sensitivity experienced in the first exposure image is reflected in the second exposure image, and then image correction eliminates the parasitic light sensitivity, improving the accuracy of acquiring transient images. Furthermore, this method can be implemented using existing ultra-high-speed dual-frame transient imaging systems without increasing system complexity.

Description

Technical Field

[0001] This invention relates to a parasitic light sensing correction method for CMOS image sensors, specifically to a parasitic light sensing correction method for ultra-high-speed dual-frame transient images. Background Technology

[0002] CMOS image sensors have become the primary sensors in imaging system design due to advancements in manufacturing processes. However, ordinary CMOS image sensors cannot be used for continuous acquisition of transient images due to their long image data readout times. Using ultra-high-speed dual-frame image acquisition technology in conjunction with an image intensifier allows ordinary CMOS image sensors to continuously acquire two ultra-high-speed transient images. However, in global shutter-type CMOS image sensors, both the photosensitive area and the charge storage nodes collect photogenerated charges. In transient imaging, if the exposure time is too short, the proportion of photogenerated charges collected by the charge storage nodes will increase, thus affecting the accuracy of transient imaging. The photosensitivity phenomenon of charge storage nodes is also known as parasitic photosensitivity. Therefore, correcting parasitic photosensitivity in ultra-high-speed dual-frame transient imaging is of great value for accurately acquiring transient images.

[0003] Currently, corrections for the effects of parasitic light sensing mainly focus on the special design of image sensors, but such special designs increase system complexity. In addition, there are a few correction methods based on acquired images, but these methods require the light intensity of the imaging object to remain constant, making them unsuitable for transient imaging where the light intensity of the imaging target changes rapidly. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problems of high complexity of existing parasitic light sensing correction systems for ultra-high-speed dual-frame transient images, or the inapplicability of existing correction methods to transient imaging where the light intensity of the imaging target changes rapidly, and to provide a parasitic light sensing correction method for ultra-high-speed dual-frame transient images.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for parasitic light sensitivity correction of ultra-high-speed dual-frame transient images, characterized by the following steps:

[0007] Step 1: Select a global shutter type CMOS image sensor with m rows and n columns of pixels, and obtain the parasitic light sensitivity of the global shutter type CMOS image sensor, where m and n are positive integers greater than or equal to 1; Select a fast persistence type image intensifier, and obtain the persistence time of the fast persistence type image intensifier according to the fast persistence type image intensifier datasheet.

[0008] Step 2: Couple the fast-persistence image intensifier to the global shutter CMOS image sensor;

[0009] Step 3: Before the first exposure trigger signal arrives, reset the global shutter type CMOS image sensor to zero and turn off the fast persistence type image intensifier.

[0010] Step 4: After the first exposure trigger signal arrives, the global shutter type CMOS image sensor starts exposure, the fast persistence image intensifier is selected, and the first exposed image is acquired; the selection time of the fast persistence image intensifier is longer than the persistence time.

[0011] Step 5: Turn off the fast-persistence image intensifier and reset the global shutter CMOS image sensor to zero. After receiving the self-trigger signal, start the global shutter CMOS image sensor to expose, select the fast-persistence image intensifier, and acquire the background image of the first exposed image. The background image of the first exposed image can be acquired before or after the first exposed image is acquired.

[0012] Step 6: Following the methods in Steps 3-4, after the second exposure trigger signal arrives, acquire the second exposure image. The parasitic light induction of the second exposure image is reflected in the first exposure image.

[0013] Step 7: Following the method in Step 5, obtain the background image of the second exposed image;

[0014] Step 8: Perform background removal processing on the first frame exposure image obtained in step 4 and the second frame exposure image obtained in step 6, respectively, using the background image of the first frame exposure image obtained in step 5 and the background image of the second frame exposure image obtained in step 7, to obtain the background-removed image I1 of the first frame exposure image and the background-removed image I2 of the second frame exposure image. The background-removed image I2 of the second frame exposure image is the second frame exposure image CI2 after parasitic light sensing correction.

[0015] Step 9: Based on the parasitic light sensitivity of the global shutter type CMOS image sensor and the background-removed image I2 of the second frame exposure image, perform parasitic light sensitivity correction on the background-removed image I1 of the first frame exposure image to obtain the parasitic light sensitivity corrected first frame exposure image CI1, thus completing the parasitic light sensitivity correction of the two-frame transient image.

[0016] Furthermore, in step 4, the gating start time of the fast-persistence image intensifier is no earlier than the exposure start time of the global shutter CMOS image sensor; the gating end time of the fast-persistence image intensifier is no later than the exposure end time of the global shutter CMOS image sensor.

[0017] Further, in step 9, the pixel value of each pixel in the first frame exposure image CI1 after parasitic light sensing correction is calculated using the following formula:

[0018] CI1 i,j =I1 i,j -PLS i,j ×I2 i,j

[0019] Where, 0≤i≤m-1, 0≤j≤n-1, and i and j are both integers;

[0020] I1 i,j This represents the value of the pixel at coordinates (i, j) in the image I1 after removing the background from the first frame of the exposed image;

[0021] I2 i,j This represents the value of the pixel at coordinates (i, j) in the background-removed image I2 of the second frame of the exposed image;

[0022] PLS i,j This represents the parasitic light sensitivity of the pixel at coordinates (i, j) in a global shutter CMOS image sensor.

[0023] Further, in step 8, the pixel value of each pixel in the second frame exposure image CI2 after parasitic light sensing correction is calculated using the following formula:

[0024] CI2 i,j =I2 i,j

[0025] Among them, I2 i,j This represents the value of the pixel at coordinates (i, j) in the image I2 after background removal from the second frame of the exposed image.

[0026] Further, in step 5, the step of starting exposure for the global shutter-type CMOS image sensor and gating the fast-persistence image intensifier specifically involves:

[0027] The gating start time of the fast-persistence image intensifier is no earlier than the exposure start time of the global shutter CMOS image sensor; the gating end time of the fast-persistence image intensifier is no later than the exposure end time of the global shutter CMOS image sensor.

[0028] Furthermore, in step 1, the persistence time of the fast persistence image intensifier is less than the readout time of one row of pixels of the global shutter CMOS image sensor.

[0029] Further, step 2 specifically involves coupling the fast-persistence image intensifier to the global shutter CMOS image sensor via an optical cone, or directly coupling them together.

[0030] Furthermore, in step 1, the pixels of the global shutter type CMOS image sensor are provided with photosensitive areas and charge storage nodes.

[0031] Further, in step 1, the parasitic photosensitivity is the ratio of the photosensing efficiency of the charge storage node to that of the photosensitive region.

[0032] Compared with the prior art, the present invention has the following beneficial technical effects:

[0033] 1. The present invention provides a method for parasitic light induction correction of ultra-high speed dual-frame transient images. It utilizes the proportional relationship between the parasitic light induction effect on the first frame image and the second frame image in ultra-high speed dual-frame transient imaging. By controlling the exposure timing of the image sensor and the image intensifier, the parasitic light induction effect on the first frame image is reflected in the second frame image. Then, the parasitic light induction is eliminated through image correction, which can improve the accuracy of the acquired transient image.

[0034] 2. The parasitic light sensing correction method for ultra-high-speed dual-frame transient images provided by the present invention can be corrected through the original structure of the ultra-high-speed dual-frame transient imaging system without increasing the system complexity. Attached Figure Description

[0035] Figure 1 This is a flowchart of a parasitic light-sensing correction method for ultra-high-speed dual-frame transient images according to the present invention;

[0036] Figure 2 This is a timing control diagram of the image sensor and image intensifier in steps 4 and 6 of an embodiment of the parasitic light sensing correction method for ultra-high-speed dual-frame transient images of the present invention. Detailed Implementation

[0037] To make the objectives, advantages and features of the present invention clearer, the following describes in further detail a parasitic light-sensing correction method for ultra-high-speed dual-frame transient images proposed in this invention, in conjunction with the accompanying drawings and specific embodiments.

[0038] A method for parasitic light sensitivity correction of ultra-high-speed dual-frame transient images, such as... Figure 1 As shown, it includes the following steps:

[0039] Step 1: Select a global shutter type CMOS image sensor with m rows and n columns of pixels, and obtain the parasitic light sensitivity of the global shutter type CMOS image sensor according to the image sensor datasheet or experimental testing, where m and n are both integers greater than or equal to 1. The pixels of the global shutter type CMOS image sensor are configured with photosensitive areas and charge storage nodes. The parasitic light sensitivity is the ratio of the photosensitive efficiency of the charge storage nodes to that of the photosensitive areas.

[0040] Select a fast-persistence image intensifier and obtain its persistence time according to the image intensifier datasheet. The persistence time of the fast-persistence image intensifier is less than the readout time of one row of pixels on a global shutter CMOS image sensor. Denote the persistence time of the fast-persistence image intensifier as T.

[0041] Step 2: Couple the fast-persistence image intensifier to the global shutter CMOS image sensor via an optical cone, or couple them directly.

[0042] Step 3: Before the first exposure trigger signal arrives, reset the global shutter type CMOS image sensor to zero and turn off the fast persistence type image intensifier.

[0043] Step 4: After the first exposure trigger signal arrives, the global shutter type CMOS image sensor begins exposure, the fast persistence type image intensifier is gated, and the first exposed image is acquired. For example... Figure 2 As shown, the end time of the fast-persistence image intensifier's gating during the first exposure is denoted as T0, and the end time of the global shutter CMOS image sensor's exposure is denoted as T1, where T1 ≥ T0. That is, during the first exposure, the end time of the fast-persistence image intensifier's persistence is no later than the end time of the global shutter CMOS image sensor's exposure. Furthermore, during the first exposure, the start time of the fast-persistence image intensifier's gating is no earlier than the start time of the global shutter CMOS image sensor's exposure.

[0044] Step 5: Turn off the fast-persistence image intensifier and reset the global shutter CMOS image sensor to zero. Upon receiving the self-trigger signal, start the global shutter CMOS image sensor to expose, activate the fast-persistence image intensifier, and acquire the background image of the first exposed frame. Acquiring the background image of the first exposed frame can be done either before or after acquiring the first exposed frame.

[0045] Step 6: Following the methods in Steps 3-4, after the second exposure trigger signal arrives, acquire the second exposure image. The parasitic light sensing in the second exposure image will be reflected in the first exposure image. For example... Figure 2 As shown, during the second exposure, let T2 be the start time of the exposure for the global shutter CMOS image sensor, T3 be the start time of the gating of the fast-persistence image intensifier, T4 be the end time of the gating of the fast-persistence image intensifier, and T5 be the end time of the exposure for the global shutter CMOS image sensor. Then, T5 ≥ T4 > T3 ≥ T2. That is, during the second exposure, the start time T3 of the fast-persistence image intensifier is no earlier than the start time T2 of the exposure for the global shutter CMOS image sensor, and the end time T4 of the fast-persistence image intensifier is no later than the end time T5 of the exposure for the global shutter CMOS image sensor.

[0046] Step 7: Following the method in Step 5, acquire the background image of the second exposure frame. When acquiring the background images of the first and second exposures, the timing of the fast-persistence image intensifier and the global shutter CMOS image sensor is consistent with Step 4. Furthermore, the background image can be acquired either before or after the effective exposure; that is, the background image of the first exposure can be acquired before or after acquiring the first exposure frame, and the background image of the second exposure can be acquired before or after acquiring the second exposure frame.

[0047] Step 8: Perform background removal processing on the first exposure image obtained in step 4 and the second exposure image obtained in step 6 using the background image of the first exposure image obtained in step 5 and the background image of the second exposure image obtained in step 7, respectively, to obtain the background-removed image I1 of the first exposure image and the background-removed image I2 of the second exposure image. The background-removed image I2 of the second exposure image is the second exposure image CI2 after parasitic light sensing correction.

[0048] Step 9: Based on the parasitic light sensitivity of the global shutter type CMOS image sensor and the background-removed image I2 of the second frame exposure image, perform parasitic light sensitivity correction on the background-removed image I1 of the first frame exposure image to obtain the parasitic light sensitivity corrected first frame exposure image CI1, thus completing the parasitic light sensitivity correction of the two-frame transient image.

[0049] The pixel value of each pixel in the first frame of the exposed image CI1 after parasitic light sensing correction is corrected using the following formula:

[0050] CI1 i,j =I1 i,j -PLS i,j ×I2 i,j

[0051] Where 0≤i≤m-1, 0≤j≤n-1, and i and j are both integers;

[0052] I1 i,j This represents the value of the pixel at coordinates (i, j) in the image I1 after removing the background from the first frame of the exposed image;

[0053] I2 i,j This represents the value of the pixel at coordinates (i, j) in the background-removed image I2 of the second frame of the exposed image;

[0054] PLS i,j This represents the parasitic light sensitivity of pixel (i, j) in a global shutter CMOS image sensor.

[0055] The pixel value of each pixel in the second frame exposure image CI2 after parasitic light sensing correction is calculated using the following formula:

[0056] CI2 i,j =I2 i,j

[0057] Among them, I2 i,j This represents the value of the pixel at coordinates (i, j) in the image I2 after removing the background from the first frame of the exposed image.

[0058] When correcting the parasitic light sensitivity of the first exposed image (image I1 after background removal) and the second exposed image (image I2 after background removal), the pixels can be corrected in any order; it is only necessary to traverse all pixels.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present invention.

Claims

1. A method for parasitic light sensing correction of ultra-high-speed dual-frame transient images, characterized in that, Includes the following steps: Step 1: Select a global shutter type CMOS image sensor with m rows and n columns of pixels, and obtain the parasitic light sensitivity of the global shutter type CMOS image sensor, where m and n are positive integers greater than or equal to 1; Select a fast persistence type image intensifier, and obtain the persistence time of the fast persistence type image intensifier according to the fast persistence type image intensifier datasheet. Step 2: Couple the fast-persistence image intensifier to the global shutter CMOS image sensor; Step 3: Before the first exposure trigger signal arrives, reset the global shutter type CMOS image sensor to zero and turn off the fast persistence type image intensifier. Step 4: After the first exposure trigger signal arrives, the global shutter type CMOS image sensor starts exposure, the fast persistence image intensifier is selected, and the first exposed image is acquired; the selection time of the fast persistence image intensifier is longer than the afterglow time. Step 5: Turn off the fast-persistence image intensifier and reset the global shutter CMOS image sensor to zero; after receiving the self-trigger signal, start the exposure of the global shutter CMOS image sensor, select the fast-persistence image intensifier, and acquire the background image of the first exposed image. Step 6: Following the methods in Steps 3-4, after the second exposure trigger signal arrives, acquire the second exposure image. The parasitic light induction of the second exposure image is reflected in the first exposure image. Step 7: Following the method in Step 5, obtain the background image of the second exposed image; Step 8: Perform background removal processing on the first frame exposure image obtained in step 4 and the second frame exposure image obtained in step 6, respectively, using the background image of the first frame exposure image obtained in step 5 and the background image of the second frame exposure image obtained in step 7, to obtain the background-removed image I1 of the first frame exposure image and the background-removed image I2 of the second frame exposure image. The background-removed image I2 of the second frame exposure image is the second frame exposure image CI2 after parasitic light sensing correction. Step 9: Based on the parasitic light sensitivity of the global shutter type CMOS image sensor and the background-removed image I2 of the second frame exposure image, perform parasitic light sensitivity correction on the background-removed image I1 of the first frame exposure image to obtain the parasitic light sensitivity corrected first frame exposure image CI1, thus completing the parasitic light sensitivity correction of the two-frame transient image.

2. The method for parasitic light sensing correction of ultra-high-speed dual-frame transient images according to claim 1, characterized in that: In step 4, the gating start time of the fast-persistence image intensifier is no earlier than the exposure start time of the global shutter CMOS image sensor; the gating end time of the fast-persistence image intensifier is no later than the exposure end time of the global shutter CMOS image sensor.

3. The method for parasitic light sensing correction of ultra-high-speed dual-frame transient images according to claim 2, characterized in that: In step 9, the pixel value of each pixel in the first frame exposure image CI1 after parasitic light sensing correction is calculated using the following formula: CI1 i,j =I1 i,j -PLS i,j ×I2 i,j Where 0≤i≤m-1, 0≤j≤n-1, and i and j are both integers; I1 i,j This represents the value of the pixel at coordinates (i, j) in the image I1 after removing the background from the first frame of the exposed image; I2 i,j This represents the value of the pixel at coordinates (i, j) in the background-removed image I2 of the second frame of the exposed image; PLS i,j This represents the parasitic light sensitivity of the pixel at coordinates (i, j) in a global shutter CMOS image sensor.

4. The method for parasitic light sensing correction of ultra-high-speed dual-frame transient images according to claim 3, characterized in that: In step 8, the pixel value of each pixel in the second frame exposure image CI2 after parasitic light sensing correction is calculated using the following formula: CI2 i,j =I2 i,j Among them, I2 i,j This represents the value of the pixel at coordinates (i, j) in the image I2 after removing the background from the second frame of the exposed image.

5. A method for parasitic light sensing correction of ultra-high-speed dual-frame transient images according to any one of claims 1-4, characterized in that: In step 5, the step of starting the exposure of the global shutter type CMOS image sensor and gating the fast persistence type image intensifier specifically involves: The gating start time of the fast-persistence image intensifier is no earlier than the exposure start time of the global shutter CMOS image sensor; the gating end time of the fast-persistence image intensifier is no later than the exposure end time of the global shutter CMOS image sensor.

6. The method for parasitic light sensing correction of ultra-high-speed dual-frame transient images according to claim 5, characterized in that: In step 1, the persistence time of the fast persistence image intensifier is less than the readout time of one row of pixels of the global shutter CMOS image sensor.

7. The method for parasitic light sensing correction of ultra-high-speed dual-frame transient images according to claim 6, characterized in that, Step 2 specifically involves coupling the fast-persistence image intensifier to the global shutter CMOS image sensor via an optical cone, or directly coupling them together.

8. The method for parasitic light sensing correction of ultra-high-speed dual-frame transient images according to claim 7, characterized in that: In step 1, the pixels of the global shutter type CMOS image sensor are provided with photosensitive areas and charge storage nodes.

9. The method for parasitic light sensing correction of ultra-high-speed dual-frame transient images according to claim 8, characterized in that: In step 1, the parasitic photosensitivity is the ratio of the photosensing efficiency of the charge storage node to that of the photosensitive region.

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