CN105872318B - 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 PDF

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Publication number
CN105872318B
CN105872318B CN201610284179.7A CN201610284179A CN105872318B CN 105872318 B CN105872318 B CN 105872318B CN 201610284179 A CN201610284179 A CN 201610284179A CN 105872318 B CN105872318 B CN 105872318B
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ccd
transfer function
modulation transfer
resistance
signal
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CN105872318A (en
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张健
许哲
赵燕
李爱玲
白喆
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XiAn Institute of Optics and Precision Mechanics of CAS
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/80Camera processing pipelines; Components thereof
    • H04N23/81Camera processing pipelines; Components thereof for suppressing or minimising disturbance in the image signal generation

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  • Transforming Light Signals Into Electric Signals (AREA)

Abstract

The invention provides a method and a circuit capable of enhancing a modulation transfer function of a CCD camera. The method of the invention comprises the following steps: 1. and removing invalid signals: removing reset pulses in the original CCD signals, and discretizing the original CCD signals; 2. effective signal amplification: inputting the CCD signal processed in the step (1) into a low-pass filter with a quality factor Q greater than 0.5 for amplification, wherein the CCD signal generates a plurality of groups of rings, and the first ring of each group of rings is linearly related to the amplitude of the CCD signal input into the filter; AD quantification: and adjusting a sampling holding point of an AD quantization chip in the AD conversion circuit to enable the sampling holding point to fall at the extreme point of the first ringing, wherein the obtained AD quantization value is amplified to a certain extent compared with the original CCD signal, and the modulation transfer function is expressed on an image of the CCD camera to obtain a certain enhancement. The circuit has the advantages of simple structure principle, low cost, strong universality and completely controllable enhancement of the modulation transfer function.

Description

It is a kind of can intensified CCD camera modulation transfer function method and circuit
Technical field
The present invention relates to the sides that a kind of control method of CCD camera index more particularly to camera modulation transfer function adjust Method and circuit.
Background technology
CCD camera is mainly made of optical-mechanical components, CCD, driving circuit and signal processing circuit.Imageable target passes through Optical-mechanical components are imaged on the photosurface of CCD, and under the action of the driving pulse that driving circuit is provided, CCD completes light Conversion, storage, transfer and the reading of charge, to convert optical information to CCD electric signals, signal processing circuit is electric by CCD Signal is converted to the data image signal that computer can be stored, be handled.
Modulation transfer function (MTF, Modulation Transfer Function) is to weigh CCD camera imaging performance One of important indicator, which characterizes CCD cameras to by the characterization ability according to object boundary:High modulation transfer function shows figure It is that objective contour is fuzzy on the image as upper i.e. target has clearly profile, the performance of low modulation transfer function.Influence CCD camera Modulation transfer function because being known as camera optical system, ccd sensor and ccd signal processing circuit.The tune of camera optical system Modulation trnasfer function cutoff frequency by early period design and the later stage assembly influenced, once assembly be completed after, modulation transfer function cut Only the value at frequency is just a determination value;Ccd sensor has a certain impact to the modulation transfer function of camera, but for one For platform camera, influence to be also certain;Influence of the ccd signal processing circuit to modulation transfer function is smaller, for big For the CCD camera of part, it can ignore.
For general CCD camera, the means for improving modulation transfer function at present are based primarily upon the side of later image processing Method, i.e. the MTF enhancings of image.Although the method for post processing of image can improve picture modulation percentage to a certain extent, past Toward the deterioration that can lead to image other parameters, such as signal noise ratio (snr) of image, therefore there is certain limitation.
Invention content
Based on background above, the present invention provides it is a kind of can intensified CCD camera modulation transfer function method and circuit.
The technical scheme is that:
It is a kind of can intensified CCD camera modulation transfer function method, be characterized in that:It includes the following steps:
(1) invalid signals are removed:Original ccd signal is inputted into correlated double sampling circuit, to remove in original ccd signal Reset pulse, while by original ccd signal discretization;
(2) useful signal amplifies:Quality factor q will be inputted through step (1) treated ccd signal>0.5 low-pass filtering Device, ccd signal amplify after by filter and generate multigroup ring, and first ring and the input filter of every group of ring Ccd signal amplitude linearity it is related;
(3) AD quantifies:The sampling holding point for adjusting AD quantizations chip in A/D converter circuit, makes it fall the institute in step (2) At the extreme point for stating first ring, then the AD quantized values obtained have certain amplification compared with original ccd signal, in CCD camera Image on show as modulation transfer function and obtain certain enhancing.
The enhancing effect of modulation transfer function is controlled by the way that the quality factor q of low-pass filter in above-mentioned steps (2) is arranged Fruit:The quality factor q of low-pass filter is bigger, and the enhancing amplitude of modulation transfer function is bigger.
By the way that the bandwidth of low-pass filter in above-mentioned steps (2) is arranged, to amplified ccd signal AD quantizations advance Row filtering, to reduce noise, improves the signal-to-noise ratio of final image.
The present invention also provides it is a kind of can intensified CCD camera modulation transfer function circuit, be characterized in that:It is wrapped Include sequentially connected correlated double sampling circuit, low-pass filter, A/D converter circuit, wherein the input terminal of correlated double sampling circuit It is connected with original ccd signal source;The correlated double sampling circuit is used to remove the reset pulse in original ccd signal, and will be former Beginning ccd signal discretization;The quality factor q of the low-pass filter>0.5, the CCD for exporting correlated double sampling circuit believes Number dynamic amplify, and amplified ccd signal have multigroup ring;The A/D converter circuit includes AD quantization chips and AD drivings Clock circuit, the ccd signal digitlization for exporting the low-pass filter;The AD driving clock circuits are for accurately controlling The sampling holding point of AD quantizations chip processed, makes sampling holding point fall in multigroup ring 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;The resistance One end of R1 is connected with the output end of the correlated double sampling circuit, separately passes through the noninverting input of resistance R2 and operational amplifier It is connected;Capacitance C1, the output end of another termination operational amplifier of capacitance C1 are further connected between the resistance R1 and resistance R2;Institute It states and is further connected with capacitance C2 between resistance R2 and the noninverting input of operational amplifier, the other end ground connection of capacitance C2;The resistance The output end of a termination operational amplifier of R3, the other end distinguish the reverse input end of connecting resistance R4 and operational amplifier;It is described The reverse input end of a termination operational amplifier of resistance R4, other end ground connection.
It is an advantage of the invention that:
1, the present invention can transmit the modulation of system in the case where the optical system of CCD camera and ccd sensor determine Function carries out certain enhancing, and circuit structure principle is simple, at low cost, versatile.Since ccd signal is passing through filter It will produce multigroup ring while amplification, those skilled in the art often consider that signal is unstable at ring, it will usually avoid In ring and its sampling nearby.And the present invention jumps out conventional thought, by sampling holding point selection first in every group of ring At the extreme point of ring, using first ring, (i.e. filter believes CCD with the relevant characteristic of input ccd signal amplitude linearity Number amplification be at ring equal proportion amplification), to amplified ccd signal carry out AD quantizations, obtained result is compared with original There is not distortion phenomenon in ccd signal, and picture quality is ensured while signal amplifies.
2, the enhancing of the modulation transfer function of the achievable CCD camera of the present invention is fully controllable, is wanted according to the use of CCD camera Seek the quality factor q of adjustment filter, it is convenient to control the enhancing of CCD camera modulation transfer function, and the quality of filter Factor Q is higher, and the enhancing amplitude of modulation transfer function is bigger.
3, the present invention is filtered ccd signal by the bandwidth of setting low-pass filter before AD quantizations, can be effective Noise is reduced, the signal-to-noise ratio of final image is improved.
Description of the drawings
Fig. 1 is the circuit diagram of the present invention;
When Fig. 2 a~2c are that CCD camera is imaged striped target, the principle of ccd signal processing procedure is shown using the present invention It is intended to, wherein Fig. 2 a are original ccd signal, and Fig. 2 b are the ccd signal after correlated-double-sampling, and Fig. 2 c are to amplify through second order filter Ccd signal afterwards;
Fig. 3 is the relation schematic diagram of the peak swing and square wave amplitude of ring.
Specific implementation mode
It elaborates with reference to the accompanying drawings and detailed description to the present invention.
The analog electrical signal of each pixel of CCD outputs includes three parts:Reset pulse A, reset level B and signal electricity Flat 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 useful signal Amplitude.The present invention uses correlated double sampling circuit to remove reset pulse A first, while obtaining reset level B and signal level B Difference, correlated double sampling circuit output be useful signal level value, as shown in Figure 2 b;Then low-pass filter is utilized The useful signal of correlated double sampling circuit output is amplified, synchronous signal will produce multigroup shake after by low-pass filter Bell, only illustrates three groups of rings Z1, Z2 and Z3 in Fig. 2 c, and every group there are two rings;Finally to amplified useful signal into Row AD quantizations obtain the gray value of each pixel, and sampled point is made to fall the peak of first ring in every group of ring when AD quantifies At (paddy), at Z11, Z21 and Z31 as illustrated in fig. 2 c.
Based on above-mentioned principle, it is provided by the present invention can the method for intensified CCD camera modulation transfer function include following step Suddenly:
(1) invalid signals are removed:Original ccd signal is inputted into correlated double sampling circuit, to remove in original ccd signal Reset pulse, while by original ccd signal discretization;
(2) useful signal amplifies:Quality factor q will be inputted through step (1) treated ccd signal>0.5 low-pass filtering Device (Q is bigger, and the enhancing amplitude of modulation transfer function is bigger), ccd signal amplifies after by filter and generates multigroup ring, And first ring of every group of ring is related to the ccd signal amplitude linearity of input filter;
(3) AD quantifies:The sampling holding point for adjusting AD quantizations chip in A/D converter circuit, makes it fall the institute in step (2) At the extreme point for stating first ring, then the AD quantized values obtained have certain amplification compared with original ccd signal, in CCD camera Image on show as modulation transfer function and obtain certain enhancing.
By the way that the bandwidth of low-pass filter in above-mentioned steps (2) is arranged, to amplified ccd signal AD quantizations advance Row filtering, to reduce noise, improves the signal-to-noise ratio of final image.
Invention also provides it is a kind of can intensified CCD camera modulation transfer function circuit, as shown in Figure 1, it includes Sequentially connected correlated double sampling circuit, low-pass filter and A/D converter circuit;Wherein, the input terminal of correlated double sampling circuit with Original ccd signal source is connected, for removing the reset pulse in original ccd signal, and by original ccd signal discretization;Low pass The quality factor q of filter>0.5, the ccd signal dynamic for exporting correlated double sampling circuit is amplified;A/D converter circuit packet AD quantization chips and AD driving clock circuits are included, the ccd signal for exporting low-pass filter digitizes;AD drives clock electricity Road is used to accurately control the sampling holding point of AD quantization chips.
Second-order low-pass filter can be used in above-mentioned low-pass filter, and the second-order low-pass filter that the present invention uses includes operation Amplifier, resistance R1, R2, R3, R4, capacitance C1, C2.The output end of a termination correlated double sampling circuit of resistance R1, the other end Capacitance C1 and resistance R2 are met respectively;The output end of another termination operational amplifier of capacitance C1;The other end of resistance R2 connects respectively The noninverting input and capacitance C2 of operational amplifier;The other end of capacitance C2 is grounded;One end of resistance R4 is grounded, another termination fortune Calculate the reverse input end of amplifier;The reverse input end of a termination operational amplifier of resistance R3, the other end connect operation and put respectively The output end and resistance R4 of big device.
Below by taking CCD camera is imaged black and white strip target as an example, the present invention is illustrated to modulation transfer function Enhancing effect.
If CCD camera is imaged black and white strip target, the spatial frequency of striped target is the limit cut-off of camera The picture of frequency, striped target is suitable with CCD pixel dimensions, and after precisely aligning, the image of acquisition is also black and white strip.It is logical Contrast transfer function (CTF, the Contrast Transfer of camera can be calculated by crossing the gray scale of black and white strip Function),(DN is gray value).Contrast transfer function CTF is carried out in Fu Leaf is unfolded to can be obtained the modulation transfer function of camera, has modulation to pass in the case where not considering Fourier expansion high-order term Delivery functionSince the gray scale of final image is actually each pixel signal after AD quantizations As a result, the contrast transfer function CTF of event camera can also be calculated using signal level, therefore in no filtered device The contrast transfer function of camera when enhanced processing
A quality factor q is arranged before signal AD quantizations in the present invention>0.5 second-order low-pass filter, ccd signal (square-wave signal) will produce ring after by filter, as shown in figure 3, first ring amplitude of every group of ring is shaken with square wave Relationship between width isΔ V1 is square wave amplitude, Δ V1=V1-V2.Adjust AD The sampled point of quantization enables it fall (Z11, Z21, Z31 as illustrated in fig. 2 c at the peak (paddy) of first ring of the ring at every group Place), the contrast transfer function of such cameraAs can be seen that in this case, phase The CTF lifting capacitys of machine areCorrespondingly, the lifting capacity of modulation transfer function isAdjustment filter The quality factor q of wave device, it will be able to obtain different modulation transfer function enhancing effects.

Claims (6)

1. it is a kind of can intensified CCD camera modulation transfer function method, it is characterised in that:Include the following steps:
(1) invalid signals are removed:Original ccd signal is inputted into correlated double sampling circuit, to remove the reset in original ccd signal Pulse, while by original ccd signal discretization;
(2) useful signal amplifies:Quality factor q will be inputted through step (1) treated ccd signal>0.5 low-pass filter, Ccd signal amplifies after by filter and generates multigroup ring, and first ring and the input filter of every group of ring Ccd signal amplitude linearity is related;
(3) AD quantifies:The sampling holding point for adjusting AD quantizations chip in A/D converter circuit makes it fall described in step (2) the At the extreme point of one ring, then the AD quantized values obtained have certain amplification compared with original ccd signal, in the figure of CCD camera Modulation transfer function is shown as on picture obtains certain enhancing.
2. it is according to claim 1 it is a kind of can intensified CCD camera modulation transfer function method, it is characterised in that:It is described The quality factor q of low-pass filter is bigger in step (2), and the enhancing amplitude of modulation transfer function is bigger.
3. it is according to claim 2 it is a kind of can intensified CCD camera modulation transfer function method, it is characterised in that:It is described By the way that the bandwidth of low-pass filter is arranged in step (2), amplified ccd signal is filtered before AD quantizations.
4. it is a kind of can intensified CCD camera modulation transfer function circuit, it is characterised in that:Including sequentially connected correlated-double-sampling Circuit, low-pass filter, A/D converter circuit, wherein the input terminal of correlated double sampling circuit is connected with original ccd signal source;
The correlated double sampling circuit is used to remove reset pulse in original ccd signal, and by original ccd signal discretization;
The quality factor q of the low-pass filter>0.5, the ccd signal dynamic for exporting correlated double sampling circuit is amplified, And amplified ccd signal has multigroup ring;
The A/D converter circuit includes AD quantization chips and AD driving clock circuits, for export the low-pass filter Ccd signal digitizes;The AD driving clock circuits are used to accurately control the sampling holding point of AD quantization chips, and sampling is made to keep Point is fallen in multigroup ring at the extreme point of first ring.
5. it is according to claim 4 it is a kind of can intensified CCD camera modulation transfer function circuit, it is characterised in that:It is described Low-pass filter is second-order low-pass filter.
6. it is according to claim 5 it is a kind of can intensified CCD camera modulation transfer function circuit, it is characterised in that:It is described Second-order low-pass filter includes operational amplifier, resistance R1, resistance R2, resistance R3, resistance R4;One end of the resistance R1 and institute The output end for stating correlated double sampling circuit is connected, and is separately connected with the noninverting input of operational amplifier by resistance R2;The electricity It is further connected with capacitance C1, the output end of another termination operational amplifier of capacitance C1 between resistance R1 and resistance R2;The resistance R2 and Capacitance C2, the other end ground connection of capacitance C2 are further connected between the noninverting input of operational amplifier;A termination of the resistance R3 The output end of operational amplifier, the other end distinguish the reverse input end of connecting resistance R4 and operational amplifier;The one of the resistance R4 Terminate the reverse input end of operational amplifier, other end ground connection.
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