CN112399171B

CN112399171B - TDICCD aerial camera focal plane detection method

Info

Publication number: CN112399171B
Application number: CN201910753852.0A
Authority: CN
Inventors: 刘志明; 王昊; 李清军; 刘学吉
Original assignee: Changchun Institute of Optics Fine Mechanics and Physics of CAS
Current assignee: Changchun Institute of Optics Fine Mechanics and Physics of CAS
Priority date: 2019-08-15
Filing date: 2019-08-15
Publication date: 2021-07-13
Anticipated expiration: 2039-08-15
Also published as: CN112399171A

Abstract

The invention discloses a TDICCD aerial camera focal plane detection method, which is characterized in that the TDICCD is subjected to multi-stage partition, namely, the TDICCD with the original total stage number of N and single output is divided into N areas, the stage number of each area is N/N, and the single output of the original TDICCD is changed into N outputs; the wedge-shaped optical glass is cut in front of the TDICCD to change the optical path during focus detection, multi-focal plane position imaging is achieved, namely each sub-area corresponds to one focal plane position, the definition of an image formed by each focal plane represents the defocusing degree, n focal plane positions of the same scene can be imaged through one-time scanning, n images are obtained, finally the best focal plane position is obtained and recorded according to the contrast of the definition evaluation function of the image of each area, after focus detection is finished, the wedge-shaped optical glass is cut out, the best focal plane position after cutting out is converted from the best focal plane position recorded during cutting, in this way, focal plane detection can be achieved through one-time scanning imaging, and the focus detection efficiency and precision are improved.

Description

TDICCD aerial camera focal plane detection method

Technical Field

The invention belongs to the technical field of aerospace imaging, and particularly relates to a TDICCD aerial camera focal plane detection method.

Background

In order to obtain a clear image, a TDICCD long-focus aerial camera (hereinafter, referred to as a camera) usually performs a focal plane search before aerial imaging, and currently, a self-collimation focus detection method or a traditional image focus detection method is generally used. The auto-collimation focus detection method adopts a hill climbing method to search the best focal plane position in the total focusing stroke, the method has long search time and low convergence speed, and in addition, under the complicated aviation condition, the structure independence of a focus detection photosensitive element and an imaging element (TDICCD) adopted by the auto-collimation focus detection can generate certain influence on the focus detection precision; the existing image focus detection algorithm can only image the multi-focal plane position of the same scene to detect the focal plane, however, the TDICCD camera is a linear array camera, and a rotating mechanical structure is needed to scan the scene during imaging, so that the single scanning period can reach 3 seconds, and if 20 focal plane positions are changed to image, the minute order is needed. The aerial camera has the advantages that the flying speed of the aerial camera is high, the scene change is high, the aim pointing of the visual axis of the camera needs to be fixed for imaging the same scene, however, under the high-speed flying state of the aerial camera, the aim staring for one minute is difficult to keep due to the limitation of the structure of the camera, and therefore the existing image focus detection algorithm cannot meet the use requirement of the TDICCD aerial camera.

Disclosure of Invention

In view of this, the present invention provides a method for detecting a focal plane of a TDICCD aerial camera, which can complete imaging of multiple focal plane positions of the same scene through one-time scanning, perform focal plane detection, and improve efficiency and accuracy of focus detection.

A TDICCD aerial camera focal plane detection method comprises the following steps:

step 1, uniformly dividing the total row number of the TDICCD sensor into at least 2 parts, and obtaining at least two partitions on the TDICCD sensor;

step 2, placing a piece of wedge-shaped glass capable of covering the whole photosensitive area on the TDICCD sensor; the thickness of the wedge-shaped glass corresponding to each partition on the TDICCD sensor is the same; the incremental optical path length of the wedge glass in each section, which is caused by the material thickness, is given by the formula Δ x ═ AL' (n)^*-1); where Δ x is the path increment, n^*The refractive index of the wedge-shaped glass is adopted, and A is the size of the top angle of the wedge-shaped glass; l' is the distance from the lower surface of the wedge-shaped glass under the partition to the TDICCD sensor;

step 3, the aerial camera performs sweep imaging on the same target along the TDI direction, and if each partition generates an image correspondingly, n images of the same target are generated;

step 4, aiming at each image obtained in the step 3, obtaining a definition evaluation function value of each image; determining a partition with the maximum evaluation function value, and then determining an optical path increment delta x corresponding to the partition as the optimal focal plane position;

and 5, removing the wedge-shaped glass, and moving the photosensitive surface of the TDICCD to the optimal focal plane position to finish the focusing process.

Preferably, a sobel digital image processing algorithm is selected to obtain the definition evaluation function value of each image.

The invention has the following beneficial effects:

the invention provides a TDICCD aerial camera focal plane detection method, which is characterized in that the TDICCD is subjected to multi-stage partition, namely, the TDICCD with the original total stage number of N and single output is divided into N areas, the stage number of each area is N/N, and the single output of the original TDICCD is changed into N outputs; the method comprises the steps of cutting wedge-shaped optical glass in front of a TDICCD (time division integrated circuit CD) to change an optical path during focus detection, realizing multi-focal plane position imaging, namely, each sub-area corresponds to one focal plane position, the definition of an image formed by each focal plane represents the defocusing degree, finishing imaging of n focal plane positions of the same scene through one-time scanning to obtain n images, finally obtaining and recording the optimal focal plane position according to the contrast of the definition evaluation function of the image of each area, cutting out the wedge-shaped optical glass after focus detection is finished, and converting the optimal focal plane position after cutting out from the optimal focal plane position recorded during cutting. Therefore, focal plane detection can be completed through one-time scanning imaging, and the efficiency and the precision of focus detection are improved.

Drawings

Fig. 1 is a schematic diagram of the operational principle before and after partitioning the tdicpcd.

Fig. 2 is a schematic view of the principle of focus detection.

FIG. 3 is a theoretical plot of the multi-focal plane position sharpness evaluation function.

Fig. 4 is a schematic diagram (540 x 540) of a simulated scene object (target).

Fig. 5 is a graph showing the actual performance of the multi-focal-plane position sharpness evaluation function.

Detailed Description

The invention is described in detail below by way of example with reference to the accompanying drawings.

According to the invention, by utilizing the imaging characteristics of the TDICCD sensor, after the TDICCD is partitioned, in the one-time scanning process of the camera, each partition of the TDICCD images the same target area for multiple times according to the time and space sequence, wherein the number of the partitions is determined according to the total number of lines of the TDICCD and the number of lines required by each area. The optical path step length between different TDICCD partitions is a fixed value, the optimal focal plane position is found by applying a sobel image processing algorithm based on fuzzy deviation estimation after imaging, and a definition evaluation function theoretical curve graph is shown in FIG. 3.

The specific implementation steps are as follows:

step 1, uniformly dividing the total row number N of the TDICCD sensor into N parts, thus obtaining N partitions on the TDICCD sensor, wherein each partition is provided with N/N rows; wherein n is determined according to actual requirements, and the minimum value is 2; the larger n is, the higher the detection precision is;

step 2, as shown in fig. 2, a piece of wedge-shaped glass capable of covering the whole photosensitive area is placed on the TDICCD sensor; the thickness of the wedge-shaped glass corresponding to each partition on the TDICCD sensor is the same, so that the imaging definition of the same partition is the same, and the definition of different partitions is different.

It should be noted that the thickness of the wedge-shaped glass is determined according to the total range of focal plane variation of the aerial camera: if the total range of focal plane change is-400 mu m, namely the total travel is 800 mu m, the TDICCD is divided into 20 areas, and the increment of the optical path of the wedge-shaped glass corresponding to each area is 40 mu m, so that the same scene area image of the whole 800 mu m defocusing range can be obtained by taking a picture once. The incremental optical path length resulting from the thickness of the wedge of glass is given by the formula Δ x ═ AL' (n)^*-1); where Δ x is the path increment, n^*Is the wedge glass index of refraction. A is a wedge-shaped glass vertex angle; l' is the distance from the lower surface of the wedge-shaped glass to the detector;

and 3, the aerial camera performs sweeping imaging on the same target along the TDI direction, and if each partition generates an image correspondingly, n images of the same target are generated. In which fig. 4 is a photographed target.

Step 4, selecting a sobel digital image processing algorithm aiming at each image obtained in the step 3 to obtain a definition evaluation function value of each image; in this embodiment, 20 evaluation function values are obtained by corresponding to 20 partitions, and 40 function values are obtained by interpolating the evaluation function values, where a curve is shown in fig. 5; the larger the defocusing degree is, the lower the function amplitude is; the closer to the ideal focal plane, the maximum evaluation function value is; and determining the partition with the maximum evaluation function value, and then determining the optical path increment delta x corresponding to the partition as the optimal focal plane position.

And 5, removing the wedge-shaped glass, controlling a motor to drive an actuating mechanism to move the photosensitive surface of the TDICCD to the optimal focal plane position, and finishing the focusing process.

The TDICCD aerial camera focal plane detection method comprises the steps of partitioning a TDICCD sensor, placing wedge-shaped glass on the TDICCD sensor, enabling each partition to correspond to different defocus amounts, obtaining a definition evaluation value of each partition through one-time sweep imaging, and selecting the defocus amount corresponding to the maximum evaluation value, namely the focal plane position to be adjusted by a focusing reflector in a camera system; compared with the traditional multiple-sweep imaging focus detection method, the method can detect the optimal focal plane through one-time imaging, greatly shortens the detection time, improves the efficiency, and is well suitable for the imaging mode of the TDICCD aerial camera.

Example (b):

step 1, a certain long-focus camera is taken as an example for the test camera, and a 200-level TDICCD detector and a CameraLink interface which are customized by DALSA are adopted. The allocation of the TDICCD is divided into 20 areas, each area has 10 rows, which corresponds to TDICCD with 10 levels per area.

And 2, the focal length of the camera optical system is 1500mm, and the half focal depth is 70 mu m.

And 3, the total range of focal plane change is-400 mu m, the total travel is 800 mu m, the TDICCD is divided into 20 areas, the change increment of the wedge-shaped glass corresponding to each area is 40 mu m, and therefore the same scene area image in the whole defocusing range of 800 mu m can be obtained by taking a picture once.

And 4, selecting a sobel algorithm by an image definition evaluation function to generate an evaluation curve (as shown in FIG. 5). And finding a peak point, recording the position corresponding to the peak point, and calculating the position of the optimal focal plane by combining the thickness of the wedge-shaped glass.

The focal plane detection method is utilized in a laboratory to realize the focusing of a long-distance target, and the long-distance target imaging simulated by the collimator is tested and verified, and the target imaging is shown in figure 4, so that the effectiveness of the method is verified.

In summary, the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A TDICCD aerial camera focal plane detection method is characterized by comprising the following steps:

step 2, placing a piece of wedge-shaped glass capable of covering the whole photosensitive area on the TDICCD sensor; the thickness of the wedge-shaped glass corresponding to each partition on the TDICCD sensor is the same; the incremental optical path length of the wedge glass in each section, which is caused by the material thickness, is given by the formula Δ x ═ AL' (n)^*-1); where Δ x is the path increment, n^*The refractive index of the wedge-shaped glass is adopted, and A is the size of the top angle of the wedge-shaped glass; l' is the distance from the surface of the wedge glass under the partition, which is far away from the TDICCD sensor, to the TDICCD sensor;

3, the aerial camera performs sweeping imaging on the same target along the TDI direction, and if each partition generates an image correspondingly, at least 2 images of the same target are generated;

2. The TDICCD aerial camera focal plane detection method of claim 1, wherein a sobel digital image processing algorithm is selected to obtain a sharpness evaluation function value of each image.