Four-exposure image acquisition method

Abstract

The invention discloses a four-exposure image acquisition method, belongs to a non-contact image acquisition technology, and aims to solve the problem that high-frequency and large-view flow field measurement cannot be realized simultaneously because a laser and a camera are not matched in the prior art. Equipment used in the method comprises two groups of convex lenses, a pyramid reflector, two groups of reflectors, an image sensor and a diaphragm, an optical signal of an object to be measured passes through the lenses and the diaphragm and then is divided into two paths by the pyramid reflector to reach corresponding channels, and the optical signal is captured by the image sensor after passing through the reflectors. The two groups of sensors are exposed for four times in one period, the time difference dt1 of two times of exposure of the first sensor is equal to the time difference dt3 of two times of exposure of the second sensor, and the exposure interval dt2 of the two sensors can be adjusted to be 1 / 2000 s to (1 / 200-1 / 2000) s. According to the invention, the signal acquisition efficiency is high, the intensity of each picture is consistent, and the velocity field measurement of the overall frequency of 200Hz and the local highest frequency of 2000Hz can be realized by matching with a multi-pulse laser.

Description

TECHNICAL FIELD

[0001] The present application relates to the non-contact image acquisition technology, and in particular to a four-exposure image acquisition method. BACKGROUND

[0002] Particle Image Velocimetry (PIV) is the most commonly used non-contact flow field measurement technology, and its physical logic is simple and effective: micron-level tracer particles are scattered in the flow field, and the target plane is illuminated with a laser sheet with a thickness of about 1mm; the camera is exposed twice in the same frame period, recording the particle displacement of Δt≈10-50μs, and the instantaneous two-dimensional velocity vector field is obtained through the cross-correlation algorithm. Due to the concentration of sheet light energy and the shortness of camera shutter to hundreds of nanoseconds, this method has the three advantages of "non-contact, global, and quantitative", and has become a benchmark tool for research on turbulence, combustion, and aerodynamic noise. However, when researchers try to improve "high frequency" and "large field of view" at the same time, due to the energy density limitation of the material, the laser cannot have high energy and high frequency at the same time. A kind of fixed frequency and variable frequency multi-pulse laser device can realize multiple exposures in one cycle, and the exposure time interval is variable, for example, four-exposure laser. However, there is no four-exposure camera on the market, which cannot form a set of flow field measurement system with it. The high-speed inter-frame camera can compress the time interval between two frames to the level of hundreds of nanoseconds, but it still cannot realize "four exposures in the same frame", and the core obstacle is that the "charge-reading" link is designed alternately frame by frame, rather than frame-by-frame time-sharing buffer. Therefore, an image acquisition method capable of realizing four exposures in one cycle is needed to realize high-frequency and large-field-of-view flow field measurement technology. SUMMARY

[0003] Based on the above shortcomings, the purpose of the present application is to provide a four-exposure image acquisition method to realize the goal of four-time image acquisition in the same field of view, and to realize the flow field measurement with high frequency and large field of view.

[0004] The technical solution adopted in this invention is as follows: A four-exposure image acquisition method, the equipment used includes a first convex lens, a second convex lens, a pyramidal reflector, a first mirror, a second mirror, a first image sensor, a second image sensor, and an aperture. The first mirror and the first image sensor constitute a first channel, and the second mirror and the second image sensor constitute a second channel. The light signal of the object under test passes sequentially through the first convex lens, the second convex lens, and the aperture, and is split into two paths by the pyramidal reflector. The first path is changed in direction by the first mirror of the first channel and then captured by the first image sensor. The second path is... The light path direction is changed by the second mirror of the second channel and then captured by the second image sensor; the two sets of image sensors generate four exposures in one cycle. The first image sensor generates two exposures with a time difference of dt1, and the time elapsed is dt2. The second image sensor generates two exposures with a time difference of dt3. dt1 and dt3 are equal, and the time dt2 is variable. The time interval between the first exposure and the two cross-frame exposures of the first image sensor is 1 / 200s. The adjustable range of dt2 is 1 / 2000s to (1 / 200-1 / 2000)s, thus forming a time-variable four exposure.

[0005] Furthermore, this method is used with a four-exposure camera and a multi-pulse laser to measure the velocity field with an overall frequency of 200 Hz and a local maximum frequency of 2000 Hz.

[0006] The present invention has the following advantages and beneficial effects:

[0007] (1) Compared with the transmission-type optical path of the traditional optical system, the aperture optical system adopts the total reflection optical path, which has a wider spectral response and makes it easier to obtain a flat reflection spectrum across the entire band.

[0008] (2) The signals of each frame of the aperture beam splitting system are reflected signals, which completely solves the problem of inconsistent intensity of transmitted and reflected signals caused by traditional beam splitting optical systems, resulting in better intensity consistency of each frame.

[0009] (3) Compared with traditional beam splitting systems, aperture beam splitting systems can achieve higher optical reflectivity, thereby achieving higher signal acquisition efficiency.

[0010] (4) The aperture beam splitting system adopts polyhedral pyramidal reflection beam splitting, which is more compact and lightweight than the traditional beam splitting system.

[0011] In conclusion, the application adopts a reflective aperture splitting design scheme and combines with the channel interval time independent control technology to realize real split imaging of two channels, has pixel level optical imaging position alignment accuracy between channels, and has excellent time and space resolution. In addition, both channel imaging adopts cross-frame imaging technology, and through external control, the time difference between the second exposure of the first channel and the first exposure of the second channel is adjustable in time sequence. Unlike the existing double-exposure camera, the four-exposure image acquisition method of the application can perform four exposures in a single sampling period, wherein the exposure time of each exposure is adjustable, the time interval of the second and third exposures is adjustable in time sequence, and the adjustable range can reach the microsecond level. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 is a four-exposure image acquisition principle diagram of the application;

[0013] Figure 2 is a four-exposure image acquisition method working principle diagram of the application; DETAILED DESCRIPTION

[0014] The application will be further described below with examples in conjunction with the drawings.

[0015] Example 1:

[0016] In conjunction with Figure 1 A four-exposure image acquisition method, the equipment used includes a first convex lens (2), a second convex lens (3), a prismatic reflector (4), a first reflector (5), a second reflector (6), a first image sensor (7), a second image sensor (8), and a diaphragm (9), the first reflector (5) and the first image sensor (7) constitute a first channel, the second reflector (6) and the second image sensor (8) constitute a second channel, and the light signal of a measured object (1) passes through the first convex lens (2), the second convex lens (3), and the diaphragm (9) in sequence, is divided into two paths by the prismatic reflector (4), the first path changes the light path direction through the first reflector (5) of the first channel and is then captured by the first image sensor (7), and the second path changes the light path direction through the second reflector (6) of the second channel and is then captured by the second image sensor (8); the two groups of image sensors generate four exposures in one period, the first image sensor (7) generates two exposures with a time difference of dt1 through cross-frame technology, and the second image sensor (8) generates two exposures with a time difference of dt3 through cross-frame technology after a time of dt2, wherein dt1 is equal to dt3, and the time dt2 is variable; the time interval of the first exposure of the two cross-frame exposures of the first image sensor (7) is 1 / 200 s, and the adjustable range of dt2 is 1 / 2000 s to (1 / 200-1 / 2000) s, so as to form four exposures with variable time sequence.

[0017] The method is used for four-exposure camera to cooperate with multi-pulse laser to measure the speed field with overall frequency of 200 Hz and local maximum frequency of 2000 Hz.

[0018] Embodiment 2

[0019] The flow field measurement workflow of four-exposure is as follows:

[0020] (1) When the camera uses the method of the application to collect images, the diaphragm is mainly used to control the amount of light entering the camera, and the aperture size is adjusted to adapt to different shooting environments and needs. The light passes through two groups of lenses into the prismatic mirror, at this time the light is divided into two, respectively into two channels, after the reflection mirror, the light is captured by the image sensor and converted into a light signal for storage.

[0021] (2) The light passes through the first channel to complete twice imaging in the time interval dt1 on the image sensor by cross-frame technology, and is stored; after the time interval dt2, the light passes through the second channel to complete twice imaging in the time interval dt3 on the image sensor by cross-frame technology, and is stored. Wherein dt1 is equal to dt3, and dt2 is time-adjustable, and the adjustable range is 1 / 2000s~(1 / 200-1 / 2000)s, so that four times of exposure in a cycle is completed and the time interval is adjustable.

Claims

1. A four-exposure image acquisition method, characterized in that: The equipment used includes a first convex lens (2), a second convex lens (3), a pyramidal reflector (4), a first mirror (5), a second mirror (6), a first image sensor (7), a second image sensor (8), and an aperture (9). The first mirror (5) and the first image sensor (7) constitute the first channel, and the second mirror (6) and the second image sensor (8) constitute the second channel. The light signal of the object under test (1) passes through the first convex lens (2), the second convex lens (3), and the aperture (9) in sequence. It is split into two paths by the pyramidal reflector (4). The first path changes the light path direction through the first mirror (5) of the first channel and then passes through the first image sensor (7). The first image sensor (7) captures two exposures with a time difference of dt1 and an elapsed time of dt2. The second image sensor (8) captures two exposures with a time difference of dt3. dt1 and dt3 are equal, and the time dt2 is variable. The time interval between the first exposure and the second exposure of the first image sensor (7) is 1 / 200s. The adjustable range of dt2 is 1 / 2000s to (1 / 200-1 / 2000)s, thus forming a time-variable four-exposure sequence.

2. The four-exposure image acquisition method according to claim 1, characterized in that: This method is used with a four-exposure camera and a multi-pulse laser to measure the velocity field with an overall frequency of 200 Hz and a local maximum frequency of 2000 Hz.

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