Imaging system with high static modulation transfer function

Abstract

The present invention relates to the field of imaging systems, and in particular to an imaging system with a high static modulation transfer function, comprising an optical system, an imaging controller and a detector. For an area array detector, the static modulation transfer function of the area array detector is improved by reducing the filling rate. For a back-illuminated detector, sub-pixel-level shading is performed on some pixels of the back-illuminated detector to reduce the filling rate. The time delay integration in the digital domain is used to improve the light energy and signal-to-noise ratio of the area array detector or the back-illuminated detector, so that the dynamic modulation transfer function of the output image can be further improved while ensuring that the original signal-to-noise ratio remains unchanged or higher. For a time delay integration detector, the static modulation transfer function of the charge transfer direction of the time delay integration detector is improved by reducing the filling rate in the charge transfer direction, and the light energy loss is compensated by improving the integration order of the time delay integration detector, so as to solve the problem that the dynamic modulation transfer function is relatively low relative to the vertical charge direction.

Description

Technical Field

[0001] The invention belongs to the technical field of imaging systems, and in particular relates to an imaging system with a high static modulation transfer function. Background Art

[0002] For a detector with a filling rate of 100%, the maximum light energy utilization rate can be obtained, and the static modulation transfer function determined by the sampling aperture will not exceed 0.637; while for a detector with a filling rate of less than 100%, the static modulation transfer function determined by the sampling aperture will exceed 0.637, and may even be close to 1, but there is a problem of insufficient light energy utilization. If the filling rate of the detector in one direction is 50%, the static modulation transfer function determined by the sampling aperture in this direction is 0.9, which is nearly 50% higher than that of a detector with a filling rate of 100%.

[0003] Under the same incident light energy conditions, the light energy received by the detector mainly depends on the area, fill rate, quantum efficiency and integration order of the detector, thus determining the maximum signal-to-noise ratio of the imaging system. The modulation transfer function of the imaging system depends on the product of the modulation transfer function of the optical system, the static modulation transfer function of the detector and the dynamic modulation transfer function of the imaging system.

[0004] One way to solve the problem of insufficient light energy is to perform time-delay integration by accumulating multiple signal exposures. If there is image shift mismatch during the time-delay integration process, the modulation transfer function will be lost during the signal exposure accumulation process. In addition, for charge transfer detectors, as the number of integration levels increases, the loss of the modulation transfer function caused by the charge transfer efficiency will further increase; as the fill rate decreases, the dynamic modulation transfer function improvement brought by uniform charge transfer may also decrease; therefore, it is necessary to conduct a comprehensive evaluation based on parameters such as the number of integration levels and the fill rate to obtain the best balance between the signal-to-noise ratio related to light energy and the modulation transfer function related to imaging clarity. Summary of the invention

[0005] In view of this, the present invention aims to provide an imaging system with a high static modulation transfer function to solve the technical problem that current imaging systems are difficult to achieve an optimal balance between the signal-to-noise ratio related to light energy and the modulation transfer function related to imaging clarity.

[0006] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0007] An imaging system with a high static modulation transfer function includes an optical system, an imaging controller and a detector. An object to be imaged is imaged on the detector through the optical system, and image data output by the detector is modulated by the imaging controller and then output;

[0008] When the detector is a front-illuminated area array detector, the size of the photosensitive part of the pixel in the front-illuminated area array detector in both directions is smaller than the size of the pixel element in both directions, and the light energy and signal-to-noise ratio are improved by time delay integration in the digital domain; the size of the pixel element in both directions is set to a and b, and the size of the photosensitive part in the pixel in both directions is set to n and m, n<a, m<b, then:

[0009] The ratio of the static modulation transfer function improvement of the horizontal direction of the front-illuminated area array detector is: ;

[0010] The ratio of the static modulation transfer function improvement in the vertical direction of the front-illuminated area array detector is: ;

[0011] The integral level ratio of the light energy loss of the front-illuminated array detector to be improved is: ;

[0012] When the detector is a back-illuminated area array detector, pixels in some areas of the back-illuminated area array detector are plated with light-blocking materials for sub-pixel light shielding, and light energy and signal-to-noise ratio are improved through time delay integration in the digital domain. The sizes of the area not plated with light-blocking materials in two directions are n and m;

[0013] When the detector is a front-illuminated time-delayed integration detector, the photosensitive part of the pixel in the front-illuminated time-delayed integration detector is partially filled in the charge transfer direction, and is fully filled in the direction perpendicular to the charge transfer direction; by reducing the filling rate in the charge transfer direction of the front-illuminated time-delayed integration detector, the static modulation transfer function in the charge transfer direction of the front-illuminated time-delayed integration detector is improved, and by improving the integration order of the front-illuminated time-delayed integration detector, the light energy loss of the front-illuminated time-delayed integration detector is compensated; the size of the pixel in two directions is set to a and b respectively, and the size of the photosensitive part in the pixel in two directions is set to a and m respectively, m<b, then:

[0014] The ratio of the static modulation transfer function improvement in the horizontal direction of the front-illuminated time delay integration detector is: ;

[0015] The ratio of the static modulation transfer function improvement in the vertical direction of the front-illuminated time delay integration detector is: ;

[0016] The proportion of the integral level of light energy loss to be improved in the positive illumination time delay integration detector is: ;

[0017] The charge transfer loss caused by increasing the integration order of the positive illumination time delay integration detector is: ; In the formula, p is the maximum integration level required for the positive illumination time delay integration detector at 100% filling rate, is the charge transfer loss corresponding to the positive illumination time delay integration detector at 100% filling rate;

[0018] The dynamic modulation transfer function loss caused by the charge transfer efficiency after the positive illumination time delay integration detector increases the integration order is:

[0019]

[0020] The dynamic modulation transfer function loss caused by reducing the steps of charge transfer within a single pixel after the positive illumination time delay integration detector increases the integration level is: ; Where q is the charge transfer steps in a single pixel of a front-illuminated time-delay integration detector at 100% fill rate;

[0021] When the detector is a back-illuminated time delay integration detector, the pixel-plated light-blocking material of the back-illuminated time delay integration detector is shielded at the sub-pixel level along the charge transfer direction; the static modulation transfer function of the back-illuminated time delay integration detector in the charge transfer direction is improved by reducing the filling rate of the back-illuminated time delay integration detector in the charge transfer direction, and the light energy loss of the back-illuminated time delay integration detector is compensated by improving the integration order of the back-illuminated time delay integration detector.

[0022] Furthermore, the light beam output by the optical system is perpendicular to the photosensitive surface of the detector.

[0023] Furthermore, the optical system adopts an off-axis three-mirror optical system in the form of an adjustable secondary mirror.

[0024] Furthermore, the front-illuminated area array detector is a front-illuminated area array CCD or a front-illuminated area array CMOS, the back-illuminated area array detector is a back-illuminated area array CCD or a back-illuminated area array CMOS, the front-illuminated time delay integration detector is a front-illuminated TDICCD or a front-illuminated TDICMOS, and the back-illuminated time delay integration detector is a back-illuminated TDICCD or a back-illuminated TDICMOS.

[0025] Compared with the prior art, the invention can achieve the following beneficial effects:

[0026] (1) For area array detectors, the static modulation transfer function of the area array detector is improved by reducing the filling rate, and the time delay integration in the digital domain is used to increase the light energy and signal-to-noise ratio, thereby further improving the dynamic modulation transfer function of the output image while ensuring that the original signal-to-noise ratio remains unchanged or higher;

[0027] (2) For back-illuminated detectors, the filling rate is 100%. In order to reduce the filling rate, some pixels of the back-illuminated detector are shielded at the sub-pixel level. The light energy and signal-to-noise ratio of the back-illuminated detector are improved through time delay integration in the digital domain, thereby further improving the dynamic modulation transfer function of the output image while ensuring that the original signal-to-noise ratio remains unchanged or higher;

[0028] (3) For the time-delayed integral detector, the filling rate in the charge transfer direction is reduced and the static modulation transfer function in the charge transfer direction of the time-delayed integral detector is improved. The light energy loss is compensated by increasing the integration order of the time-delayed integral detector, and the problem that the dynamic modulation transfer function of the time-delayed integral detector is low relative to the vertical charge direction due to image shift mismatch and decreased charge transfer efficiency is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings:

[0030] Figure 1 is a schematic structural diagram of an imaging system with a high static modulation transfer function according to an embodiment of the invention;

[0031] Figure 2 2. It is a schematic diagram of pixel size of a front-illuminated area array detector according to an embodiment of the invention;

[0032] Figure 3 Schematic diagram of the pixel size of the front-illuminated time-delay integration detector described in an embodiment of the invention.

[0033] The reference numerals include: optical system 1 , detector 2 , and imaging controller 3 . DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the invention more clear, the invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described here are only used to explain the invention and do not constitute a limitation of the invention.

[0035] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0036] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0037] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0038] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0039] like Figure 1 As shown, the present invention provides an imaging system with a high static modulation transfer function, including an optical system 1, a detector 2 and an imaging controller 3. The object to be imaged is imaged on the detector 2 through the optical system 1, and the image data output by the detector 2 is modulated and output by the imaging controller 3. The optical system 1 adopts an off-axis three-reflector optical system in the form of an adjustable secondary mirror. The detector 2 adopts a planar array detector or a time-delayed integral detector. The imaging controller 3 is implemented using an FPGA of Xilinx or Fudan Micro.

[0040] When the detector 2 adopts an array detector, there are two cases: one is to adopt a front-illuminated array detector, which can be a front-illuminated array CCD or a front-illuminated array CMOS; the other is to adopt a back-illuminated array detector, which can be a back-illuminated array CCD or a back-illuminated array CMOS. When the detector 2 adopts a time-delayed integration detector, there are two cases: one is to adopt a front-illuminated time-delayed integration detector, which can be a front-illuminated TDICCD or a front-illuminated TDICMOS; the other is to adopt a back-illuminated time-delayed integration detector, which can be a back-illuminated TDICCD or a back-illuminated TDICMOS.

[0041] The following describes the detector 2 as a front-illuminated area array detector, a back-illuminated area array detector, a front-illuminated time delay integration detector, and a back-illuminated time delay integration detector.

[0042] 1. Direct-illuminated area array detector

[0043] When the detector adopts a front-illuminated area array detector, the size of the photosensitive part of the pixel in the front-illuminated area array detector in both directions is smaller than the size of the pixel element in both directions, and the light energy and signal-to-noise ratio are improved through time delay integration in the digital domain.

[0044] like Figure 2 As shown, the sizes of the pixel in two directions are set to a and b, and the sizes of the photosensitive part in the pixel in two directions are set to n and m, n<a, m<b, then:

[0045] The ratio of the static modulation transfer function improvement of the horizontal direction of the front-illuminated area array detector is: ;

[0046] The ratio of the static modulation transfer function improvement in the vertical direction of the front-illuminated area array detector is: ;

[0047] The integral level ratio of the light energy loss of the front-illuminated area array detector to be improved is: .

[0048] 2. Back-illuminated area array detector

[0049] When the detector adopts a back-illuminated area array detector, pixels in some areas of the back-illuminated area array detector are coated with light-blocking materials for sub-pixel shading, and light energy and signal-to-noise ratio are improved through time delay integration in the digital domain. The sizes of the area not coated with light-blocking materials in two directions are n and m.

[0050] Taking the filling rate of the back-illuminated area array detector in the horizontal direction and the vertical direction as 50% for example, the improvement ratio of the static modulation transfer function in the two directions of the back-illuminated area array detector is:

[0051]

[0052] Since the filling rate in the horizontal direction and the filling rate in the vertical direction are 50% each, the ratio of the photosensitive area to the pixel area is 0.5×0.5=0.25; therefore, for a back-illuminated detector with a relative filling rate of 100%, the energy received is 1 / 4, so the number of accumulations needs to be quadrupled.

[0053] In order to reduce or avoid the influence of oblique incident light, the light beam output by the optical system is required to be perpendicular to the photosensitive surface of the detector.

[0054] For front-illuminated area array detectors or back-illuminated area array detectors, the static modulation transfer function is improved by reducing the fill rate, and the time delay integration in the digital domain is used to increase the light energy and signal-to-noise ratio, thereby further improving the dynamic modulation transfer function of the output image while ensuring that the original signal-to-noise ratio remains unchanged or higher.

[0055] 3. Direct-illumination time-delay integration detector

[0056] When the detector is a front-illuminated time delay integration detector, the photosensitive part of the pixel in the front-illuminated time delay integration detector is partially filled in the charge transfer direction, and is fully filled in the direction perpendicular to the charge transfer direction; by reducing the filling rate of the front-illuminated time delay integration detector in the charge transfer direction, the static modulation transfer function of the front-illuminated time delay integration detector in the charge transfer direction is improved, and by improving the integration order of the front-illuminated time delay integration detector, the light energy loss of the front-illuminated time delay integration detector is compensated.

[0057] like Figure 3 As shown, the dimensions of the pixel in two directions are set to be a and b, and the dimensions of the photosensitive part in the pixel in two directions are set to be a and m, m<b. The maximum integration level required for the positive illumination time delay integration detector at 100% filling rate is p, and the corresponding charge transfer loss is , the charge transfer within a single pixel needs to go through q steps, then:

[0058] The ratio of the static modulation transfer function improvement in the horizontal direction of the front-illuminated time delay integration detector is: ;

[0059] The ratio of the static modulation transfer function improvement in the vertical direction of the front-illuminated time delay integration detector is: ;

[0060] The proportion of the integral level of light energy loss to be improved in the positive illumination time delay integration detector is: ;

[0061] The charge transfer loss caused by increasing the integration order of the positive illumination time delay integration detector is: ;

[0062] The dynamic modulation transfer function loss caused by the charge transfer efficiency after the positive illumination time delay integration detector increases the integration order is:

[0063] The dynamic modulation transfer function loss caused by reducing the steps of charge transfer within a single pixel after the positive illumination time delay integration detector increases the integration level is: .

[0064] 4. Back-illuminated time-delay integration detector

[0065] When the detector is a back-illuminated time delay integration detector, the pixel-plated light-blocking material of the back-illuminated time delay integration detector is shielded at the sub-pixel level along the charge transfer direction; the static modulation transfer function of the back-illuminated time delay integration detector in the charge transfer direction is improved by reducing the filling rate of the back-illuminated time delay integration detector in the charge transfer direction, and the light energy loss of the back-illuminated time delay integration detector is compensated by improving the integration order of the back-illuminated time delay integration detector.

[0066] Taking the back-illuminated time delay integration detector as an example, the filling rate in the vertical direction is 50%, the maximum number of integration levels required is 128, the charge transfer efficiency is 0.9999, and the charge transfer is a four-phase working mode, the proportion of the static modulation transfer function in the vertical direction of the back-illuminated time delay integration detector is improved by ; However, since the filling rate in the vertical direction is 50%, the effective photosensitive area of ​​the detector is reduced to 50% of the original, so the number of time delay integration accumulations required is twice as much as before. The number of steps required for charge transfer within a single pixel is reduced from four phases to two phases, resulting in a dynamic modulation transfer function that accounts for 1 / 2 of the original times, the dynamic modulation transfer function caused by the charge transfer efficiency after increasing the integration order accounts for the original The final dynamic modulation transfer function is improved by 1.414*0.924*0.987=1.29 times.

[0067] For back-illuminated area array detectors or back-illuminated time delay integration detectors, the filling rate is 100%. In order to reduce the filling rate, some pixels of the back-illuminated detector are shielded at sub-pixel level, and the light energy and signal-to-noise ratio of the back-illuminated detector are improved through time delay integration in the digital domain, thereby further improving the dynamic modulation transfer function of the output image while ensuring that the original signal-to-noise ratio remains unchanged or higher.

[0068] For front-illuminated time delay integration detector or back-illuminated time delay integration detector, the filling rate in the charge transfer direction is reduced, the static modulation transfer function in the charge transfer direction of the time delay integration detector is improved, and the light energy loss is compensated by increasing the integration order of the time delay integration detector, so as to solve the problem that the dynamic modulation transfer function of the time delay integration detector is low relative to the vertical charge direction due to image shift mismatch and decreased charge transfer efficiency.

[0069] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the disclosure of the present invention can be performed in parallel, sequentially or in different orders, as long as the desired results of the technical solution disclosed in the present invention can be achieved, and this document does not limit this.

[0070] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An imaging system with a high static modulation transfer function, comprising an optical system and an imaging controller, characterized in that: It also includes a detector, the object to be imaged is imaged on the detector through the optical system, and the image data output by the detector is modulated by the imaging controller and then output; When the detector is a front-illuminated area array detector, the size of the photosensitive part of the pixel in the front-illuminated area array detector in both directions is smaller than the size of the pixel element in both directions, and the light energy and signal-to-noise ratio are improved by time delay integration in the digital domain; the size of the pixel element in both directions is set to a and b, and the size of the photosensitive part in the pixel in both directions is set to n and m, n<a, m<b, then: The ratio of the static modulation transfer function improvement of the horizontal direction of the front-illuminated area array detector is: ; The ratio of the static modulation transfer function improvement in the vertical direction of the front-illuminated area array detector is: ; The integral level ratio of the light energy loss of the front-illuminated array detector to be improved is: ; When the detector is a back-illuminated area array detector, pixels in some areas of the back-illuminated area array detector are plated with light-blocking materials for sub-pixel light shielding, and light energy and signal-to-noise ratio are improved through time delay integration in the digital domain. The sizes of the area not plated with light-blocking materials in two directions are n and m; When the detector is a positive illumination time delay integration detector, the photosensitive part of the pixel in the positive illumination time delay integration detector is partially filled in the charge transfer direction, and is fully filled in the direction perpendicular to the charge transfer direction; By reducing the filling rate of the front-illuminated time delay integration detector in the charge transfer direction, improving the static modulation transfer function of the front-illuminated time delay integration detector in the charge transfer direction, and improving the integral order of the front-illuminated time delay integration detector to compensate for the light energy loss of the front-illuminated time delay integration detector; the size of the pixel in the two directions is set to a and b respectively, and the size of the photosensitive part in the pixel in the two directions is set to a and m respectively, m<b, then: The ratio of the static modulation transfer function improvement in the horizontal direction of the front-illuminated time delay integration detector is: ; The ratio of the static modulation transfer function improvement in the vertical direction of the front-illuminated time delay integration detector is: ; The proportion of the integral level of light energy loss to be improved in the positive illumination time delay integration detector is: ; The charge transfer loss caused by increasing the integration order of the positive illumination time delay integration detector is: ; Where p is the maximum integration level required for the positive illumination time delay integration detector at 100% filling rate, is the charge transfer loss corresponding to the positive illumination time delay integration detector at 100% filling rate; The dynamic modulation transfer function loss caused by the charge transfer efficiency after the positive illumination time delay integration detector increases the integration order is: The dynamic modulation transfer function loss caused by reducing the steps of charge transfer within a single pixel after the positive illumination time delay integration detector increases the integration level is: ; Where q is the charge transfer steps in a single pixel of a front-illuminated time-delay integration detector at 100% fill rate; When the detector is a back-illuminated time delay integration detector, the pixel-plated light-blocking material of the back-illuminated time delay integration detector is shielded at the sub-pixel level along the charge transfer direction; the static modulation transfer function of the back-illuminated time delay integration detector in the charge transfer direction is improved by reducing the filling rate of the back-illuminated time delay integration detector in the charge transfer direction, and the light energy loss of the back-illuminated time delay integration detector is compensated by improving the integration order of the back-illuminated time delay integration detector.

2. The imaging system with high static modulation transfer function according to claim 1, characterized in that: The light beam output by the optical system is perpendicular to the photosensitive surface of the detector.

3. The imaging system with high static modulation transfer function according to claim 2, characterized in that: The optical system adopts an off-axis three-mirror optical system with an adjustable secondary mirror.

4. The imaging system with high static modulation transfer function according to any one of claims 1 to 3, characterized in that: The front-illuminated area array detector is a front-illuminated area array CCD or a front-illuminated area array CMOS, the back-illuminated area array detector is a back-illuminated area array CCD or a back-illuminated area array CMOS, the front-illuminated time delay integration detector is a front-illuminated TDICCD or a front-illuminated TDICMOS, and the back-illuminated time delay integration detector is a back-illuminated TDICCD or a back-illuminated TDICMOS.

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