An algorithm for correcting the lower limit of early saturation of a camera with automatic exposure

Abstract

The present invention discloses a method for controlling the automatic exposure function of a camera to a gray level setting. The method includes determining a critical exposure time of an image sensing device of the camera, where the critical exposure time of the image sensing device of the camera is the exposure time when a first sensed gray level of the image sensing device of the camera is configured to a target gray level, and the sensed gray level is configured in a decreasing trend of the sensed gray level value; exposing the image sensing device of the camera to obtain a second sensed gray level, and comparing the second sensed gray level of the critical exposure time with the target gray level. If the second sensed gray level is configured at least at the target gray level, the exposure of the image sensing device of the camera is limited to the critical exposure time.

Description

Technical Field

[0001] The present invention relates to an algorithm for correcting the early saturation lower limit problem of a camera related to its automatic exposure algorithm. Specifically, the present invention relates to an algorithm for correcting the early saturation lower limit problem of a charge-coupled device camera related to its automatic exposure algorithm. Background Art

[0002] The automatic exposure (AE) control of digital cameras (such as complementary metal oxide semiconductor (CMOS) and charge-coupled device (CCD)) remains a problem that requires careful study because there are still some problems with these technologies. The applicant has found that on some cameras, due to the traditional assumption of a linear or piecewise linear relationship between the exposure time and the image brightness level, there is a problem that the target gray level does not converge in AE control, resulting in underexposed images displayed by these cameras. Generally, the automatic exposure control algorithm regards the relationship between the exposure time and the image brightness level as linear or piecewise linear, without considering that the image brightness level of a certain camera can never recover from its early declining image brightness level. Therefore, according to the gray level setting of the camera AE function, the automatic exposure algorithm based only on the image brightness level will never reach its target gray level. In addition, for the AE control strategy for strong light, in low light conditions, it may inadvertently cause it to malfunction.

[0003] It is necessary to ensure that this early saturation lower limit problem encountered by the CCD camera when exposed to strong light and weak light can be successfully AE-controlled. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide an automatic exposure method that provides a solution to a non-converging automatic exposure program that is only based on the image brightness received on the image sensing device. Another object of the present invention is to provide an automatic exposure method that corrects the non-convergence of the prior art automatic exposure program due to the early saturation lower limit problem of the camera, so as to present an appropriate brightness or gray level on the output or display of the image sensing device. Another object of the present invention is to provide an automatic exposure method that uses a fast-converging solution to correct the early saturation lower limit of the camera. Another object of the present invention is to provide an automatic exposure method that is easy to implement.

[0005] Technical solution: A method for controlling the automatic exposure (AE) function of a camera to a gray-level setting, the method comprising: establishing a critical exposure time of an image sensing device of the camera, wherein the critical exposure time of the image sensing device of the camera is an exposure time when a first sensed gray level of the image sensing device of the camera is configured at a target gray level according to the gray-level setting, and the sensed gray level is configured with a tendency to decrease the sensed gray-level value; exposing the image sensing device of the camera to obtain a second sensed gray level of the image sensing device of the camera; and comparing the second sensed gray level of the critical exposure time with the target gray level, and if the second sensed gray level is at least configured at the target gray level, limiting the exposure of the image sensing device of the camera to the critical exposure time.

[0006] In one embodiment, the method further comprises determining a minimum required exposure time of the image sensing device of the camera. If the second sensed gray level is at least configured at the target gray level, the determining step comprises exposing the image sensing device of the camera for an exposure time less than the critical exposure time and obtaining a third sensed gray level of the image sensing device of the camera. If the third sensed gray level is not the same as the target gray level, the determining step is repeated until the third sensed gray level is the same as the target gray level to obtain the minimum required exposure time.

[0007] In one embodiment, the camera is an imaging device adapted to operate according to the principle of an image sensing device of a charge-coupled device camera.

[0008] Advantageous effects: In one embodiment, the method or algorithm of the present invention provides a non-converging automatic exposure program solution, wherein the non-converging automatic exposure program is only based on the image brightness received at the image sensing device; in one embodiment, the method or algorithm of the present invention provides an automatic exposure method that corrects the non-convergence of the prior art automatic exposure program due to the problem of the early saturation lower limit of the camera, so as to present an appropriate brightness or gray level on the output of the image sensing device or the display; in one embodiment, the present automatic exposure method provides a solution for fast convergence; in all embodiments of the present invention, the solution of the non-converging automatic exposure program and the optimization program for reducing the convergence delay can be implemented without significantly affecting the computational cost. Description of the Drawings

[0009] Figure 1 is a system diagram showing the input of an image sensing device and an output device whose image brightness is controlled by an automatic exposure program of a control device;

[0010] Figure 2 is a graph related to the image brightness and exposure time of an image sensing device, showing the theoretical or assumed gray-scale response of a conventional CCD image sensing device;

[0011] Figure 3 is a graph related to the image brightness and exposure time of an image sensing device, showing the early saturation lower limit problem of a CCD image sensing device;

[0012] Figure 4 is a flowchart describing an automatic exposure program applicable to correcting the early saturation lower limit problem of a CCD image sensing device;

[0013] Figure 5 is a flowchart describing an automatic exposure program applicable to correcting the early saturation floor problem of a CCD image sensing device and shortening the convergence time of this program;

[0014] Among them, control device 2; image sensing device 4, such as charge-coupled device (CCD) pixels; display 6; step 8 of determining the critical exposure time; step 10 of exposing the image sensing device; step 12 of comparing the second sensed gray level of the critical exposure time with the target gray level and limiting the exposure time of the image sensing device; step 14 of determining the minimum required exposure time; user or observer 16; saturation point 18; curve 20 corresponding to strong light exposure; curve 22 corresponding to weak light exposure. Detailed implementation

[0015] As used herein, the term "about" means approximate, roughly, approximately or within the range of. When the term "about" is used in combination with a numerical range, it modifies the numerical range by extending the upper and lower boundaries of the set value. Generally, the term "about" as used herein modifies the value with a variance of 20% above or below the specified value.

[0016] Figure 1It is a system diagram showing the input of the image sensing device 4 and the output device whose image brightness is controlled by the automatic exposure program of the control device 2. The image sensing device 4 is a charge-coupled device (CCD) of a camera or any charge-coupled device adapted to operate according to the principle of an image sensing device of a (charge-coupled device) camera. The image sensing device 4 and the display 6 are both functionally connected to the control device 6. In one example, an image sensing device 4 includes a semiconductor divided into pixels. When light irradiates a pixel, the pixel can be filled with one or more electrons. The grayscale output of the pixel corresponds to the number of electrons in the pixel. Before operating on this output, the output is received on the control device 2 so that a modified output based on the output received from the image sensing device 4 can be provided to the display 6, where the image brightness of the image can be recognized by the user 16. In this example, the modified output is displayed to the user 16. However, this modified output can also be used by an image processing algorithm, where the appropriate brightness or grayscale of the modified output can affect the way features are extracted from the modified output. Therefore, it is important to configure the modified output with appropriate brightness. The control device 2 represents any device configured to receive the output from the image sensing device 4, generate a modified output using, for example, a resident automatic exposure program or a remote automatic exposure program, and transmit the modified output to the display.

[0017] Figure 2 It is a graph related to the image brightness and exposure time of the image sensing device, showing the theoretical or assumed grayscale response of a conventional CCD image sensing device. It should be noted that the grayscale response basically rises proportionally with time until time t2, at which point additional exposure does not change the grayscale level as the grayscale level reaches the saturation point 18. Figure 2 It depicts the image brightness-exposure time curve applicable to some CCD image sensing devices, as well as the modified output or automatic exposure applied output received on the display. However, the applicant has found that in some charge-coupled device systems, anomalies where the image brightness is not proportional to the exposure time do occur. Figure 3 It illustrates one such example. Figure 3It is a graph related to the image brightness and exposure time of an image sensing device, showing the early saturation lower limit problem of a CCD image sensing device. It should be noted that curve 20 shows an increasing trend before reaching the peak, and then decreases to a low gray level even at longer exposure times. The common practice to try to solve this problem is to modify the output from the image sensing device to have a sufficiently significant gain to increase the descending part of curve 20. However, it should be noted that by applying a large gain, when the image sensing device is exposed to low light, the displayed image will be overexposed and the background noise increases significantly. Therefore, in the current solutions to the early saturation lower limit problem, the potential problems that may occur when exposed to low light conditions must be considered.

[0018] Figure 4 It is a flowchart describing an automatic exposure program applicable to correcting the early saturation lower limit problem of a CCD image sensing device. In one embodiment, by intercepting and replacing the program operating on the output of the image sensing device 4, this method can be applied to an existing CCD system. In another embodiment, this method can be applied as a whole to the new construction of a charge coupled device system. In controlling the automatic exposure function of a camera to a gray level setting, for example, for an 8-bit system, "desired automatic exposure G1" is 200, this method includes: establishing the critical exposure time 8 of the image sensing device of the camera, where the critical exposure time t3 of the image sensing device of the camera is the exposure time when the first sensed gray level of the image sensing device of the camera is configured at the target gray level according to the gray level setting, and the sensed gray level is configured at the exposure time with a tendency to decrease the sensed gray level value. For example, for the same 8-bit system with "target AE GL" of 220 and configured according to the gray level setting of 200. The target gray level is essentially a gray level setting with a tolerance. The first sensed gray level is configured at t3 with a tendency to decrease the sensed gray level value. Compare this with the point where "target AE G1" is configured at 220 and time t1. The t3 point is selected because, although t1 represents a shorter exposure duration, setting the exposure time to t1 will seriously affect the convergence of automatic exposure under low light conditions represented by curve 22. In other words, for the case where the image sensing device usually needs to be alternately exposed to strong light and low light conditions, setting the exposure time to t1 only benefits the convergence of the strong light scenario as t1 < t3, that is, with a smaller delay amount. This step can be performed through the calibration or measurement process of the image sensing device and its corresponding AE program;

[0019] Expose the image sensing device 10 of the camera to light to obtain a second sensed gray level of the image sensing device of the camera. At this time, an image will be captured by the camera, so the image sensing device is exposed; and compare the second sensed gray level 12 of the critical exposure time (or t3) with the target gray level 220. If the second sensed gray level is at least configured at the target gray level, limit the exposure of the image sensing device of the camera to the critical exposure time. It should be noted that the action of limiting the exposure of the image sensing device of the camera to the critical exposure time will not be performed under low light conditions because the second sensed gray level will not be at least set at the target gray level of 220, thus avoiding any negative impact that may be imposed on the automatic exposure process under low light conditions. Figure 5 is a flowchart of an automatic exposure program that describes an automatic exposure program suitable for correcting the early saturation floor problem of a CCD image sensing device and shortening the convergence time of the program. When this automatic exposure program is applied to another exposure with similar light conditions, this embodiment can be used to reduce the exposure time to reach the target gray level. In this embodiment, the method further includes determining a minimum required exposure time 14 of the image sensing device 4 of the camera. If the second sensed gray level is at least configured at the target gray level 220, the determining step includes exposing the image sensing device of the camera for an exposure time (or t3) less than the critical exposure time and obtaining a third sensed gray level of the image sensing device of the camera. Wherein if the third sensed gray level is not the same as the target gray level, iterate the determining step until the third sensed gray level is the same as the target gray level 220 to obtain the minimum required exposure time. It should be noted that the iteration of the target gray level of 220 is in the direction of reducing the exposure time, rather than in the direction of increasing the exposure time, which will cause the automatic exposure program to never be positioned in the direction of the target gray level.

Claims

1. A method for controlling the automatic exposure function of a camera to a gray-level setting, characterized in that, The method includes: determining a critical exposure time of an image sensing device of the camera, wherein the critical exposure time of the image sensing device of the camera is an exposure time at which a first sensed gray level of the image sensing device of the camera is configured at a target gray level according to a gray level setting, and the first sensed gray level is configured at a decreasing trend of sensed gray level values; exposing the image sensing device of the camera to obtain a second sensed gray level of the image sensing device of the camera; comparing the second sensed gray level at the critical exposure time with the target gray level, and if the second sensed gray level is arranged at least at the target gray level, limiting the exposure of the image sensing device of the camera to the critical exposure time.

2. The method according to claim 1, characterized in that It further includes determining a minimum required exposure time of the image sensing device of the camera. If the second sensed gray level is set at least at the target gray level, the determining step includes exposing the image sensing device of the camera at an exposure time less than the critical exposure time and obtaining a third sensed gray level of the image sensing device of the camera. If the third sensed gray level is not the same as the target gray level, the determining step is repeated until the third sensed gray level is the same as the target gray level to obtain the minimum required exposure time.

3. The method according to claim 1, wherein The camera is an imaging device adapted to operate according to the principle of an image sensing device of a charge-coupled device camera.

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