CN112449122B - Nonlinear quantization error correction algorithm for pulse array type image sensor - Google Patents

Nonlinear quantization error correction algorithm for pulse array type image sensor Download PDF

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CN112449122B
CN112449122B CN201910744080.4A CN201910744080A CN112449122B CN 112449122 B CN112449122 B CN 112449122B CN 201910744080 A CN201910744080 A CN 201910744080A CN 112449122 B CN112449122 B CN 112449122B
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nonlinear
linear
light intensity
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image sensor
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CN112449122A (en
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徐江涛
苗津
高志远
李嘉文
刘伯文
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Tianjin University Marine Technology Research Institute
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/70—SSIS architectures; Circuits associated therewith
    • H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
    • H04N25/77—Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
    • H04N25/772—Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components comprising A/D, V/T, V/F, I/T or I/F converters
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/40—Extracting pixel data from image sensors by controlling scanning circuits, e.g. by modifying the number of pixels sampled or to be sampled

Abstract

Pulse arrayA nonlinear quantization error correction algorithm of a column-type image sensor provides a method for correcting nonlinear quantization errors according to the generation reason of integral nonlinear response. Then outputting pulse interval to the sensorT nolineOr number of pulsesN nolineProcessing to obtain linear pulse intervalT lineAnd number of linear pulsesN line. Finally, restoring the light intensity information through the obtained linear data to eliminate the nonlinear response quantization error; the algorithm can eliminate the quantization error of the pulse array type image sensor caused by integral nonlinear response in two quantization modes of PWM and PFM, and achieves the purpose of improving the quantization precision of the pulse array type image sensor.

Description

Nonlinear quantization error correction algorithm for pulse array type image sensor
Technical Field
The invention relates to the field of image sensors, in particular to the field of light intensity quantization of a pulse array type image sensor, namely a nonlinear quantization error correction algorithm of the pulse array type image sensor.
Background
With the rapid development of machine vision fields such as automatic driving, real-time object tracking and the like, high-speed, high-precision and low-power consumption image sensors become research hotspots. The traditional frame frequency image sensor has the defects of information redundancy, low time precision, large power consumption and the like, so that the traditional frame frequency image sensor cannot be applied to the field of high-speed machine vision. The pulse array type image sensor adopts a digital pixel structure, and realizes data compression and high-speed work by directly outputting pulse signals. Two quantization methods, pwm (pulse Width modulation) and pfm (pulse Frequency modulation), are usually used to quantize the light intensity information of the pulse array image sensor. But the application condition of the two quantization methods described above is an integral linear response. In the practical operation of the sensor, the integral response of the pixel is nonlinear, which causes quantization errors in the quantization methods of PWM and PFM.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a non-linear quantization error correction algorithm of a pulse array type image sensor, which can eliminate the quantization error of the pulse array type image sensor caused by integral non-linear response in two quantization modes of PWM and PFM, and achieves the purpose of improving the quantization precision of the pulse array type image sensor.
The pixel integration curve of the pulse array type image sensor is shown in FIG. 1, whereinV rstIn order to reset the voltage, the voltage is reset,V refis a reset voltage; the solid line is an ideal linear response, and the dotted broken line is an actual nonlinear response; t1 represents a linear integration time, and t2 represents a non-linear integration time. It is obvious that the deviation of the two isV pixGradually, i.e. a non-linear quantization error is introduced.
A non-linear quantization error correction algorithm of a pulse array type image sensor provides a method for correcting a non-linear quantization error according to the generation reason of integral non-linear response, and the implementation steps of the algorithm are shown in figure 2: firstly, judging a light intensity quantization method of the sensor, and selecting a corresponding correction mode according to the quantization method. Then outputting pulse interval to the sensorT nolineOr number of pulsesN nolineProcessing to obtain linear pulse intervalT lineAnd number of linear pulsesN line. And finally, restoring the light intensity information through the obtained linear data to eliminate the nonlinear response quantization error.
When the light intensity is quantized in a PWM mode, under ideal linear conditions, the light intensity informationI ph1Expressed as:
Figure 131021DEST_PATH_IMAGE001
whereinC pd0Is a static capacitance of a photodiode and is,min order to be a slope factor of the capacitance,
Figure 693589DEST_PATH_IMAGE002
0 is the built-in potential of the photodiode,V diffis the difference between the reset voltage and the reference voltage. Under nonlinear conditions, light intensity informationI ph1Can be expressed as:
Figure 910944DEST_PATH_IMAGE003
whereinV diff In order to reset the voltage, the voltage is reset,V diffis a reference voltage, becauseI ph1 =I ph2Obtaining:
Figure 773726DEST_PATH_IMAGE004
according to non-linear pulse intervalT nolineAnd equation (3) can obtain the linear pulse intervalT lineAnd finally, restoring the light intensity information through the formula (1) to eliminate the nonlinear quantization error.
Under the condition of PFM quantized light intensity, the number of linear pulsesN1=INT(T period/T line) Number of nonlinear pulsesN2=INT(T period/T noline) From equation (3), we can obtain:
Figure 686843DEST_PATH_IMAGE005
can pass throughN2And the formula (4) to obtain the number of pulses under ideal conditionsNAnd 1, eliminating the nonlinear quantization error.
A pulse array image sensor nonlinear quantization error correction algorithm can restore pulse intervals or pulse numbers under a linear condition according to nonlinear reading of a pulse array image sensor, and then restore light intensity information according to linear data to eliminate nonlinear response quantization errors and improve the quantization accuracy of the pulse array image sensor.
Drawings
FIG. 1 is a graph of a pixel integration of a pulse array image sensor;
FIG. 2 is a diagram of the steps of the correction algorithm.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, a detailed description of the embodiments of the present invention will be given below with reference to examples.
Testing a pulse array image sensor with a pixel array size of 400 multiplied by 400 and processing output data thereof to verify the algorithm effect, wherein the input light intensity is 1500lux uniform light intensity, and the integration period isT period=20ms，V rst=3.3V，V ref=1.1V， C pd0=7fF，m= 0.7. Defining PFM quantization error
Figure 2287DEST_PATH_IMAGE006
Comprises the following steps:
Figure 288912DEST_PATH_IMAGE007
whereinI inIn order to input the light intensity,I out_PFMthe light intensity is output for PFM quantization mode. Defining PWM quantization error
Figure 727240DEST_PATH_IMAGE008
Comprises the following steps:
Figure 136224DEST_PATH_IMAGE009
whereinI inIn order to input the light intensity,I out_PWMthe light intensity is output for the PWM quantization mode. Processing the output data of the image sensor according to the algorithm and calculating the quantization error, and finally obtaining the image sensor with the image quality under the PFM quantization condition,
Figure 735702DEST_PATH_IMAGE006
from 12.1% to 1.2%; when the sensor employs the PWM quantization method,
Figure 891264DEST_PATH_IMAGE008
from 10.5% to 0.5%; the result proves that the algorithm has the correction effect on the nonlinear quantization errorIs quite obvious.

Claims (1)

1. A nonlinear quantization error correction algorithm of a pulse array type image sensor is characterized in that: the method comprises the following specific steps: firstly, judging a light intensity quantization method of the sensor, and selecting a corresponding correction mode according to the quantization method; then outputting nonlinear pulse interval T to the sensornolineAnd the number N2 of nonlinear pulses is processed to obtain the linear pulse interval TlineAnd the number of linear pulses N1; finally, restoring the light intensity information through the obtained linear data to eliminate the nonlinear response quantization error;
when the light intensity is quantized in a PWM mode, under the ideal linear condition, the light intensity information Iph1Expressed as:
Figure FDA0003612949160000011
wherein C ispd0Is the photodiode static capacitance, m is the capacitance slope factor,
Figure FDA0003612949160000012
for built-in potential of photodiode, VrstFor reset voltage, VdiffIs the difference between the reset voltage and the reference voltage; under nonlinear conditions, light intensity information Iph2Can be expressed as:
Figure FDA0003612949160000013
wherein VrstFor reset voltage, VrefIs a reference voltage, due to Iph1＝Iph2Obtaining:
Figure FDA0003612949160000014
according to nonlinear pulse interval TnolineAnd equation (3) can obtain linear pulseSeparate TlineFinally, the light intensity information is restored through the formula (1) to eliminate the nonlinear quantization error;
linear pulse number under the condition of PFM quantification light intensity
Figure FDA0003612949160000015
Number of nonlinear pulses
Figure FDA0003612949160000016
Wherein T isperiodFor the integration period, it can be obtained from equation (3):
Figure FDA0003612949160000017
the number N1 of linear pulses under ideal conditions can be obtained through N2 and formula (4), and nonlinear quantization errors are eliminated.
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CN105791718A (en) * 2016-03-21 2016-07-20 天津大学 SPAD image sensor based on event-driven reading mode
CN107454350A (en) * 2017-08-25 2017-12-08 电子科技大学 Pulse width modulation type image sensor circuit and its processing method

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CN105791718A (en) * 2016-03-21 2016-07-20 天津大学 SPAD image sensor based on event-driven reading mode
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