CN105872318A - Method and circuit capable of enhancing modulation transfer function of CCD camera - Google Patents
Method and circuit capable of enhancing modulation transfer function of CCD camera Download PDFInfo
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- CN105872318A CN105872318A CN201610284179.7A CN201610284179A CN105872318A CN 105872318 A CN105872318 A CN 105872318A CN 201610284179 A CN201610284179 A CN 201610284179A CN 105872318 A CN105872318 A CN 105872318A
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- ccd
- transfer function
- modulation transfer
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
- H04N23/80—Camera processing pipelines; Components thereof
- H04N23/81—Camera processing pipelines; Components thereof for suppressing or minimising disturbance in the image signal generation
Abstract
The invention provides a method and circuit capable of enhancing the modulation transfer function of a CCD camera. The method includes the following steps of 1, removing ineffective signals, wherein reset pulses in original CCD signals are removed, and meanwhile the original CCD signals are discretized; 2, amplifying effective signals, wherein the CCD signals processed in the step 1 are input into a low-pass filter with the quality factor larger than 0.5 to be amplified, meanwhile, the CCD signals can generate multiple groups of rings, and the first ring of each group of rings is in linear dependence with the amplitude of the CCD signals input into the filter; 3, carrying out AD quantization, wherein the sampling and holding point of an AD quantization chip in an AD conversion circuit is adjusted to fall to the extreme points of the first rings, so that an obtained AD quantization value is amplified to some degree compared with that of the original CCD signals, in other words, on an image of the CCD camera, the modulation transfer function is enhanced to some degree. The circuit is simple in structure and principle, low in cost and high in universality, and the enhancement of the modulation transfer function is completely controllable.
Description
Technical field
The present invention relates to the control method of a kind of CCD camera index, particularly relate to method and circuit that camera modulation transfer function adjusts.
Background technology
CCD camera is mainly made up of optical-mechanical components, CCD, drive circuit and signal processing circuit.Imageable target is imaged on the photosurface of CCD by optical-mechanical components, under the effect of the driving pulse provided at drive circuit, CCD completes the conversion of optical charge, stores, shifts and read, thus converting optical information to the CCD signal of telecommunication, the CCD signal of telecommunication is converted to the data image signal that computer can store, process by signal processing circuit.
Modulation transfer function (MTF) (MTF, Modulation Transfer Function) it is one of important indicator weighing CCD camera imaging performance, which characterizes CCD camera to by according to the sign ability of object boundary: high modulation transfer function (MTF) show on image i.e. target have profile clearly, low modulation transfer function (MTF) to show on image, i.e. objective contour obscures.Affect CCD camera modulation transfer function (MTF) because have camera optical system, ccd sensor and ccd signal process circuit.The modulation transfer function (MTF) cut-off frequency of camera optical system is assembled affected by early stage design and later stage, and after once assembly be completed, modulation transfer function (MTF) value at cut-off frequency is just one to determine value；The modulation transfer function (MTF) of camera is had a certain impact by ccd sensor, but for a camera, its impact is also certain；It is smaller on the impact of modulation transfer function (MTF) that ccd signal processes circuit, for major part CCD camera, can ignore.
For general CCD camera, the means improving modulation transfer function (MTF) at present are based primarily upon the MTF enhancing of the method that later image processes, i.e. image.Although the method for post processing of image can improve picture modulation percentage to a certain extent, but frequently can lead to the deterioration of other parameters of image, such as signal noise ratio (snr) of image, therefore there is certain limitation.
Summary of the invention
Based on background above, the invention provides a kind of can the method for intensified CCD camera modulation transfer function and circuit.
The technical scheme is that
A kind of can the method for intensified CCD camera modulation transfer function, it is characterized in that it comprises the following steps:
(1) invalid signals is removed: original ccd signal is inputted correlated double sampling circuit, to remove the reset pulse in original ccd signal, simultaneously by original ccd signal discretization；
(2) useful signal amplify: will through step (1) process after ccd signal input quality factor q > 0.5 low pass filter, ccd signal amplifies after by wave filter and produces organizes ring more, and first ring often organizing ring is relevant to the ccd signal amplitude linearity of input filter；
(3) AD quantifies: adjusts AD in A/D convertor circuit and quantifies the sampling holding point of chip, it is made to fall described in step (2) at the extreme point of first ring, the AD quantized value then obtained has certain amplification than original ccd signal, shows as modulation transfer function (MTF) and obtain certain enhancing on the image of CCD camera.
The reinforced effects of modulation transfer function (MTF) is controlled: the quality factor q of low pass filter is the biggest, and the enhancing amplitude of modulation transfer function (MTF) is the biggest by arranging the quality factor q of low pass filter in above-mentioned steps (2).
By arranging the bandwidth of low pass filter in above-mentioned steps (2), the ccd signal after amplifying was filtered before AD quantifies, to reduce noise, improves the signal to noise ratio of final image.
Present invention also offers a kind of can the circuit of intensified CCD camera modulation transfer function, it is characterized in that correlated double sampling circuit that it includes being sequentially connected with, low pass filter, A/D convertor circuit, wherein, the input of correlated double sampling circuit is connected with original ccd signal source；Described correlated double sampling circuit is used for removing the reset pulse in original ccd signal, and by original ccd signal discretization；The quality factor q of described low pass filter > 0.5, for dynamically being amplified by the ccd signal that correlated double sampling circuit exports, and the ccd signal after amplifying has and organizes ring more；Described A/D convertor circuit includes that AD quantifies chip and AD driving clock circuit, for the ccd signal digitized exported by described low pass filter；Described AD driving clock circuit quantifies the sampling holding point of chip for accurately controlling AD, makes sampling holding point fall in the ring of described many groups at the extreme point of first ring.
Above-mentioned low pass filter is second-order low-pass filter.
Above-mentioned second-order low-pass filter includes operational amplifier, resistance R1, resistance R2, resistance R3, resistance R4；One end of described resistance R1 is connected with the outfan of described correlated double sampling circuit, and the another resistance R2 that passes through is connected with the input in the same direction of operational amplifier；The outfan of another termination operational amplifier of electric capacity C1, electric capacity C1 it is further connected with between described resistance R1 and resistance R2；The other end ground connection of electric capacity C2, electric capacity C2 it is further connected with between described resistance R2 and the input in the same direction of operational amplifier；The outfan of the one termination operational amplifier of described resistance R3, the other end connecting resistance R4 and the reverse input end of operational amplifier respectively；The reverse input end of the one termination operational amplifier of described resistance R4, other end ground connection.
The invention have the advantage that
1, the present invention can be carried out certain enhancing to the modulation transfer function (MTF) of system, and circuit structure principle be simple, low cost, highly versatile in the case of the optical system of CCD camera and ccd sensor determine.Organizing ring owing to ccd signal can be produced while being amplified by wave filter, those skilled in the art are often unstable in view of signal at ring more, it will usually avoid ring and near sampling.And the present invention jumps out conventional thought, select often organizing in ring at the extreme point of first ring by sampling holding point, utilize the characteristic (i.e. ccd signal is amplified at ring by wave filter is that equal proportion is amplified) that first ring is relevant to input ccd signal amplitude linearity, ccd signal after amplifying is carried out AD quantization, there is not distortion phenomenon than original ccd signal in the result obtained, ensure that picture quality while signal amplifies.
2, the enhancing of the modulation transfer function (MTF) that the present invention can realize CCD camera is fully controllable, the requirement that uses according to CCD camera adjusts the quality factor q of wave filter, the enhancing of CCD camera modulation transfer function (MTF) can be controlled easily, and the quality factor q of wave filter is the highest, the enhancing amplitude of modulation transfer function (MTF) is the biggest.
3, the present invention is by arranging the bandwidth of low pass filter, is filtered ccd signal before AD quantifies, and can effectively reduce noise, improves the signal to noise ratio of final image.
Accompanying drawing explanation
Fig. 1 is the circuit theory diagrams of the present invention；
Fig. 2 a～2c be CCD camera to striped target imaging time, use the present invention principle schematic to ccd signal processing procedure, wherein Fig. 2 a is original ccd signal, and Fig. 2 b is the ccd signal after correlated-double-sampling, Fig. 2 c be through second order filter amplify after ccd signal；
Fig. 3 is the peak swing relation schematic diagram with square wave amplitude of ring.
Detailed description of the invention
With detailed description of the invention, the present invention is elaborated below in conjunction with the accompanying drawings.
The analog electrical signal of each pixel of CCD output includes three parts: reset pulse A, reset level B and signal level C, as shown in Figure 2 a.Wherein, reset pulse A is invalid signals, and the difference of reset level B and signal level C is equal to the amplitude of useful signal.The present invention removes reset pulse A initially with correlated double sampling circuit, obtains the difference of reset level B and signal level B simultaneously, and the output of correlated double sampling circuit is the level value of useful signal, as shown in Figure 2 b；Then the useful signal utilizing low pass filter to export correlated double sampling circuit is amplified, and synchronous signal can produce after by low pass filter and organize ring more, is diagrammatically only by out three groups of rings Z1, Z2 and Z3, and often group has two rings in Fig. 2 c；Finally the useful signal after amplifying is carried out AD and quantifies to obtain the gray value of each pixel, make when AD quantifies sampled point fall at peak (paddy) place often organizing first ring in ring, at Z11, Z21 and Z31 as illustrated in fig. 2 c.
Based on above-mentioned principle, provided by the present invention can the method for intensified CCD camera modulation transfer function comprise the following steps:
(1) invalid signals is removed: original ccd signal is inputted correlated double sampling circuit, to remove the reset pulse in original ccd signal, simultaneously by original ccd signal discretization；
(2) useful signal amplify: will through step (1) process after ccd signal input quality factor q > 0.5 low pass filter (Q is the biggest, the enhancing amplitude of modulation transfer function (MTF) is the biggest), ccd signal amplifies after by wave filter and produces organizes ring more, and first ring often organizing ring is relevant to the ccd signal amplitude linearity of input filter；
(3) AD quantifies: adjusts AD in A/D convertor circuit and quantifies the sampling holding point of chip, it is made to fall described in step (2) at the extreme point of first ring, the AD quantized value then obtained has certain amplification than original ccd signal, shows as modulation transfer function (MTF) and obtain certain enhancing on the image of CCD camera.
By arranging the bandwidth of low pass filter in above-mentioned steps (2), the ccd signal after amplifying was filtered before AD quantifies, to reduce noise, improves the signal to noise ratio of final image.
Invention also provides a kind of can the circuit of intensified CCD camera modulation transfer function, as it is shown in figure 1, it includes correlated double sampling circuit, low pass filter and the A/D convertor circuit being sequentially connected with；Wherein, the input of correlated double sampling circuit is connected with original ccd signal source, for removing the reset pulse in original ccd signal, and by original ccd signal discretization；The quality factor q of low pass filter > 0.5, for the ccd signal that correlated double sampling circuit exports dynamically is amplified；A/D convertor circuit includes that AD quantifies chip and AD driving clock circuit, for the ccd signal digitized exported by low pass filter；AD driving clock circuit quantifies the sampling holding point of chip for accurately controlling AD.
Above-mentioned low pass filter can use second-order low-pass filter, and the second-order low-pass filter that the present invention uses includes operational amplifier, resistance R1, R2, R3, R4, electric capacity C1, C2.The outfan of the one termination correlated double sampling circuit of resistance R1, the other end meets electric capacity C1 and resistance R2 respectively；The outfan of another termination operational amplifier of electric capacity C1；The other end of resistance R2 meets input in the same direction and the electric capacity C2 of operational amplifier respectively；The other end ground connection of electric capacity C2；One end ground connection of resistance R4, the reverse input end of another termination operational amplifier；The reverse input end of the one termination operational amplifier of resistance R3, the other end meets outfan and the resistance R4 of operational amplifier respectively.
Below as a example by CCD camera carries out imaging to black and white strip target, illustrate the present invention reinforced effects to modulation transfer function (MTF).
If CCD camera carries out imaging to black and white strip target, the spatial frequency of striped target is the limit cut-off frequency of camera, and the picture of striped target is suitable with CCD pixel dimension, and after accurately alignment, the image of acquisition is also black and white strip.The contrast transfer function (CTF, Contrast Transfer Function) of camera just can be calculated by the gray scale of black and white strip,(DN is gray value).Contrast transfer function CTF is carried out Fourier expansion and can obtain the modulation transfer function of camera, in the case of not considering Fourier expansion high-order term, have modulation transfer function (MTF)Owing to the gray scale of final image is actually each pixel signal result after AD quantifies, therefore the contrast transfer function CTF of camera can also utilize signal level to calculate, the therefore contrast transfer function of camera when not having device processing and amplifying after filtering
The present invention arranged a quality factor q before signal AD quantifies > second-order low-pass filter of 0.5, ccd signal (square-wave signal) can produce ring after by wave filter, as it is shown on figure 3, the relation often organized between first ring amplitude and the square wave amplitude of ring isΔ V1 is square wave amplitude, Δ V1=V1-V2.Adjust the sampled point that AD quantifies, make it fall at peak (paddy) place (as illustrated in fig. 2 c at Z11, Z21, Z31) of first ring often organizing ring, the contrast transfer function of such cameraIt can be seen that in this case, the CTF lifting capacity of camera isAccordingly, the lifting capacity of modulation transfer function isAdjust the quality factor q of wave filter, it becomes possible to obtain different modulation transfer function reinforced effects.
Claims (6)
1. one kind can the method for intensified CCD camera modulation transfer function, it is characterised in that: include following
Step:
(1) invalid signals is removed: original ccd signal is inputted correlated double sampling circuit, former to remove
Reset pulse in beginning ccd signal, simultaneously by original ccd signal discretization；
(2) useful signal amplifies: will be through the ccd signal import prime factor after step (1) processes
The low pass filter of Q > 0.5, ccd signal amplifies after by wave filter and produces organizes ring more, and often
First ring of group ring is relevant to the ccd signal amplitude linearity of input filter；
(3) AD quantifies: adjusts AD in A/D convertor circuit and quantifies the sampling holding point of chip so that it is
Fall described in step (2) at the extreme point of first ring, then the AD quantized value obtained is than original
Ccd signal has certain amplification, shows as modulation transfer function (MTF) and obtain certain on the image of CCD camera
Enhancing.
The most according to claim 1 a kind of can the method for intensified CCD camera modulation transfer function,
It is characterized in that: in described step (2), the quality factor q of low pass filter is the biggest, modulation transfer function (MTF)
Enhancing amplitude the biggest.
The most according to claim 2 a kind of can the method for intensified CCD camera modulation transfer function,
It is characterized in that: by arranging the bandwidth of low pass filter in described step (2), to the CCD after amplifying
Signal was filtered before AD quantifies.
4. one kind can the circuit of intensified CCD camera modulation transfer function, it is characterised in that: include successively
The correlated double sampling circuit of connection, low pass filter, A/D convertor circuit, wherein, correlated double sampling circuit
Input be connected with original ccd signal source；
Described correlated double sampling circuit is used for removing the reset pulse in original ccd signal, and by original
Ccd signal discretization；
The quality factor q of described low pass filter > 0.5, for the CCD that correlated double sampling circuit is exported
Signal dynamics is amplified, and the ccd signal after amplifying has and organizes ring more；
Described A/D convertor circuit includes that AD quantifies chip and AD driving clock circuit, for by described low
The ccd signal digitized of bandpass filter output；Described AD driving clock circuit is for accurately controlling AD
Quantify the sampling holding point of chip, make sampling holding point fall described and organize the pole of first ring in ring more
At value point.
The most according to claim 4 a kind of can the circuit of intensified CCD camera modulation transfer function,
It is characterized in that: described low pass filter is second-order low-pass filter.
The most according to claim 5 a kind of can the circuit of intensified CCD camera modulation transfer function,
It is characterized in that: described second-order low-pass filter includes operational amplifier, resistance R1, resistance R2, resistance
R3, resistance R4；One end of described resistance R1 is connected, separately with the outfan of described correlated double sampling circuit
It is connected with the input in the same direction of operational amplifier by resistance R2；Between described resistance R1 and resistance R2
It is further connected with the outfan of another termination operational amplifier of electric capacity C1, electric capacity C1；Described resistance R2 and fortune
Calculate the other end ground connection being further connected with electric capacity C2, electric capacity C2 between the input in the same direction of amplifier；Described electricity
The outfan of the one termination operational amplifier of resistance R3, other end connecting resistance R4 respectively and operational amplifier
Reverse input end；The reverse input end of the one termination operational amplifier of described resistance R4, other end ground connection.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN109873923A (en) * | 2017-11-16 | 2019-06-11 | 安讯士有限公司 | The image noise reduction of modulation transfer function based on camera dome |
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