iRAY T3S Thermal Camera Performance Analysis - piseo.fr

iRAY T3S Thermal Camera Performance Analysis2020 Technical Report

1©PISEO 2020 | www.piseo.fr | iRay T3S camera performance report

Introduction


• Thanks to multiple drivers, the market for infra-red thermal imaging cameras and modules isexpanding rapidly with a multiplicity of products on offer. There is, therefore, a need for users,integrators and sensor manufacturers to be able to discriminate between available products basedon accurate and independent assessments of their performance and features.

• This report is the very first of a kind that will help thermal imaging camera and module marketactors to better understand the characteristics of such products, enabling better strategicdecision making.

• More reports will follow soon, which will allow fair comparisons of product featuresand performance.

• The following cameras and modules have either already been analyzed or are planned:

• Flir Boson 640 Pro camera (USA): available in Q4 2020

• Guide VGA 12µm (China): available Q1 2021

• Seek thermal module QVGA 12µm (USA): available Q1 2021

• Hikvision camera QQVGA 17µm (China): planned

• Teledyne Dalsa GXF (Canada): planned

Piséo’s Opinion of the iRay T3S Camera

The iRay T3S camera tested by PISEO has proven to be a good value formoney product but requires some improvements.

• We have greatly appreciated:• The good correspondence of the datasheet values with our own

measurements.• The good image quality provided thanks to a very good bolometric

sensor and a performant 3 step tone mapping process.• The Xtherm user-friendly interface.

• We have less appreciated:• The manual focus which often asks the user to search for the focus

point.• The need to de-assemble the lens from the camera for packing

purposes, which allows for dust to be deposited on the sensor.• The risk of making large temperature measurement errors if the user

has no background in thermal measurement principles.

• We did not explore:• The thermal measurement algorithm.


Objectives of the report

• This reports aims at providing a comprehensive and independent analysis of the main features,performance and imaging system architecture of the iRay-T3S camera.

• The analysis has been based on physical measurements, calculations, simulations andobservations realized in PISEO’s lab in comparison with data provided in the datasheet.

• The report presents :

• An analysis of the user functions of the camera.

• An analysis of the measured performance parameters of the embedded microbolometric sensor RTD3172.

• An analysis of the measured thermometric performance of the T3S camera.

• An assessment of the optical architecture and design.

• An analysis of the image processing flow from sensor to image as well as an assessment of image quality.

• Our opinion of the iRay-T3S camera features and performance.


PiséoThe company, created 9 years ago, specializes in the design, realization and characterization of illumination,detection and imaging systems that integrate advanced photonic technologies such as LED’s, VCSELs, laserdiodes, photodiodes, imaging sensors, material for optics...

Piséo offers application and technical analysis, optical and system design, prototyping and characterizationservices for devices using UV, VIS and IR radiation.

Piséo performs analyses in partnership with System Plus Consulting and Yole Développement, one of thecompany’s main shareholders.

Examples of completed projects and services:

Freeform optic design and

realization for streetlighting

UV-C illuminator design and realization

VCSEL based system design and realization

Imaging optical system design and realization

IR camera performance

analysisGoniophotometry

UV measurements and

photobiological risk assessment


o Introduction P 2

o Piséo’s opinion of the iRay T3S camera P 3

o Objective of the report P 4

o About Piséo P 5

o Glossary P 8

o Executive summary P 9

o T3S camera functionalities and use P34

• Camera Presentation

• Microbolometric sensor

• Packing and presentation

• Technical characteristics of the camera

• Technical characteristics of the microbolometric sensor

Handling and functionalities:

• Starting operation

• Smartphone plug-in

• Xtherm interface

• Colormaps

• Temperature measuring functions

• Temperature measurement settings

• Imaging temperature ranges

• Shutter correction error with temperature range activation - description

• Shutter correction error with temperature range activation - Details of error

• Physical connection

o Image production flow analysis P 50

• Image production – simplified pipeline

• Hardware configuration for image production

• Main hardware devices and functions

• Image retrieval

• Raw image and corrected image

o Image sensor characterization methodology P 56

• Image sensor characterization

• Image production

• Blackbody setup

• MTF measurement – description

• MTF Measurement – Slanted edge method description

• FPA temperature measurement

• Responsivity and NETD

• Linear scene dynamic

• Bad pixel detection and operability

• Non-uniformity correction and RFPN

• Thermographic function

Table of contents


o T3S imaging performance characterization P 68

• Introduction

• Responsivity, NETD, scene dynamic 20°C – 40°C

• Operability, +20°C, +40°C

• Responsivity, NETD, scene dynamic -20°C to +100°C

• Operability, -20°C, +100°C

• Dependence on ambient temperature

• FPA temperature stability

• Flat field correction

• FFC comparison with 2-point NUC

• Residual fixed pattern noise

• Thermographic response

• Shutter activation

• Image quality in extreme temperature cases

o T3S Temperature sensing analysis P 82

• Characterization methodology

• Performance and accuracy

• Influence of emissivity on the temperature measurement

• Physics of emissivity

• Application to skin temperature measurement

• Synthesis of the temperature measurement performances

o Optical design analysis P 89

• Cross sectional analysis

• Optical performances

• Control of the focus distance

• Optical analysis conclusions

o Image processing and tone mapping analysis P 94

• Methodology

• Image processing

• NUC correction

• Tone mapping

• Sharpening

• Histogram equalization

• Gamma correction

• Image processing flow chart

• Synthesis

• Images used in the analysis

o Conclusion and Opinion P109

• Synthesis of the imaging performance

• Conclusion

• PISEO’s Opinion of the iRay T3S camera

o PISEO P114

o Contact P121

Table of contents


T3S camera presentation

• The T3S camera from InfiRay is one of a portfolio of compact thermal camera plug-ins for smartphones.These cameras address consumer and industrial applications : industrial inspection, animal observation,electronic testing…

• They differ in terms of resolution and accuracy. The T3S model integrates a Raytron microbolometer dieRTD3172 17µm and presents intermediate features compared to the T2L camera (more compact) and the T3SPRO camera (more accurate).

Camera Pixel resolution

Px pitch Thermal resolution (NETD)

Temperature measurement accuracy

T2L 256x292 12µm +/-3%

T3S 384x288 17µm <60mK +/-3%

T3S PRO 384x288 17µm <60mK +/-2%

Portfolio


Microbolometric sensorPrinciple

• Bolometric sensors are thermal detectors able toconvert an electromagnetic field into electricresistance variation of a thermo sensitivematerial.

• Microbolometers are made of a thin film infraredabsorber and a bolometric resistance material(vanadium oxide or amorphous silicon). Infraredlight radiated from an object causes the absorbertemperature to increase and the bolometerresistance to decrease. This change is convertedinto a voltage for readout, by a CMOS orBiCMOS circuit fabricated on the substrate. Toinsulate the infrared sensitive resistance fromthe structure, the layers of thin film absorberand bolometer resistance is supported by legs.This assembly is a pixel, integrated on a sensorcontaining a large number of these pixels. Pixelpitch is usually 25µm, 17µm or 12µm.

• Read-out integrated circuit converts the pixelvoltage signals into a 16bit image signal.

Photosensitive area

horizontal register

vertical registerAmplifiers, sample&hold circuit, digital output

Pixel - principle

T3S bolometric sensorSource : System Plus Consulting

Pixel – SEM view

Die – optical view


T3S camera presentationTechnical characteristics of the microbolometric sensor

• The technical features referto a 17µm Voxmicrobolometer 3172 fromInfiRay.

• The claims of the thermalresolution (NETD) are slightlydifferent between the sensorand the camera.

• NETD 40mK µbolometer datasheet.

• NETD 60mK camera datasheet.

• This can be as a result of measurement setup differences (aperture etc.) and added noise sources.

14-bit digital output

T3S datasheet – Source : InfiRay10©PISEO 2020 | www.piseo.fr | iRay T3S camera performance report

Handling and functionalitiesSmartphone plug-in

• The shutter is activated immediately after camera plug-in for a flatfield correction.

• A corrected binary gray image is then produced on the screen.

• The user must focus the camera by simply rotating the lens.

• A logo is overlayed in the top right corner.


Image production

Pixel matrixROIC

Image correction, video processing,

temperature analysis

UVC interface

Data exchange:• Raw image data• Corrected image data• 8bit color mapped images• Temperature calculation

• Temperature determination functions are addedto the embedded firmware.

• Firmware applications retrieve data and processthem for a proper user visual.

• Color mapped images via Xtherm app.

• Temperature calculations.

• Raw or corrected image data used for testapplication in this report.Shutter

temperature measurement

Data bus

Shutter

Simplified pipeline

Application

• Images result from different steps of signaltreatment.

• Read-Out integration functions to digitize thepixelated signal of the bolometer.

• Correction functions to compensate for thermaldrift and non-uniformity of the pixel responses.

• Color mapping, tone mapping.


Main hardware devices and functions

• Synchronizes the 14 signals from eachbolometer to fill an array.

• Image processing:

• Shutter drive.

• NUC.

• Tone mapping.

• Color mapping.

• Temperature measurement.

• Converts the FPA temperature raw value in °Cusing the embedded algorithm.

RTD3172C Microbolometer

• Active pixel matrix: 395x295:

• Includes compensation pixels and blind pixels.

• Effective resolution: 384x288.

• ROIC processing:

• Clock frame 25Hz.

• V_sync.

• H_sync.

• Digitization 14bit.

M2S010 FPGA

Active pixel matrix Analog

treatment area

Digitization functions

(Extracted raw image with PISEO’s acquisition software)


Blackbody setupUniform and controlled temperature with a blackbody

• A controlled-temperature scene isplaced in the field of view of thecamera.

• Represented by a blackbody(HGH) regulated temperaturesurface.

• Possible to control the surfacetemperature from -15°C to+150°C.

• Accurate scene temperaturecontrol < +/-0.03 °C.

• Temperature surface uniformity0.01 °C @25°C, 0.3°C @ 50°C

• Stability 0.5mK.

• Climate chamber for ambienttemperature variations.

• 0°C to 50°C.


Responsivity / NETD / Scene dynamicRange 20°C – 40°C

• The table shows the evaluation of NETD,responsivity and scene dynamic over therange 20°C-40°C (scene temperature).

• Repeatability was observed over 5consecutive tests.

• Measured NETD value...

• XXmK measured for 40mK specified.

• No software filter was used to boostcamera characteristics.

• Responsivity and scene temperature arecoherent with the measurementtemperature range.

• The temperature range -20°C to+120°C represents XX% of the scenedynamic at 25°C ambienttemperature.

• Can be affected by ambienttemperature effect (see p 72).


OperabilityRange 20°C – 40°C

• Operability close to 100% meansall pixels are basically functional.

• Bad pixels revealed by NETDcriterion are not the same fordifferent measurements =>visualization of bad pixels isprobably not intrinsic to the pixelitself, but to the impact of noiseover the complete chain.


FFC comparison with 2-point NUC

• The resulting standard deviationvaries by X DN on the sceneamplitude [X°C to XX°C]. With atwo-point NUC, the variation canbe improved.

• A bias of XX DN is observed. It isprobably due to the long timeperiod between the factorycorrection and currentacquisition.

iRay NUC

2-point NUC processed by PISEO

Raw


Temperature measurement function

• Setting conditions :

• Ambient 25°C

• BB emissivity 0.XX

• Others :

• The measured error …

• X.X°C max , less than +/-X°C

• 1X.X% FS max, less than+/-X% full scale

• The average drift of +XX°C on thesample can be compensated by acorrection factor of -X°C to reduce themeasuring error.

• Error max +/-X°C

Performance and accuracy


Cross sectional analysis

• The objective is built from 2 chalcogenide glass lenses with aformulation similar to Schott IRG26.

• The usual manufacturing process is glass molding into lenses (LWIRspectrum allows for 10x larger surface tolerances than visiblespectrum).

• Section cut : no films were deposited :

• No anti-reflective coating

• No overmolded diffractive patterns

• No diffractive pattern (direct mold) were detected in close-up viewof the lens surfaces.

• Only asphericity coefficients could be present, not visible in thiscross-section.

• For optimization, the inner surface of lens 1 would be the best tosupport aspheric surface. However, lens 2 has lower slopes on bothsurfaces and it is more suitable and practical to produce suchaspheric profiles.

Source : System Plus Consulting


Optical performance

• The optical model derived from the cross sectiondetermines optical properties and performance. As cross-sectional data is not sufficient to derive asphericcoefficients, the model is not fully representative of thereal optic assembly. However, it can be used to assess thegeneral properties.

• This cross section is consistent with a 13-14mm focallength component, F/1 front aperture.

• Measured MTF shows MTF50 for 0.28 cycles/pixel. Opticalsimulations give MTF70 for the same spatial frequency of0.28 cycles/pixel. The difference of 20% can be explainedby the impact of tolerances. Such a difference isconsistent with a medium/good level of manufacturing ofthe optical assembly.

• Sensitivity loss of 0 up to 10% in corners can be caused bylens vignetting, depending on design.

• Distortion lower than 2.5% appears reasonable.

Responsivity - spatial variations (vignetting)

PISEO’s Opticalmodelization withZEMAX Opticstudio 20, basedon optical crosssections.


Image processing

• The test software developed by PISEO is able toretrieve the various output formats generated bythe camera : 16bit raw image, 16bit NUC correctedimage, 8bit automatic mode image.

• Only 14 of the 16 bits are used to encode thesignal.

• Between raw sensor image (top) and finalautomatic mode image (below), several imageprocessing steps based on common algorithms areapplied:

• NUC correction;

• Tone mapping consisting of different operations : sharpening, equalization, gamma correction;

• 8bit image conversion.

Raw T3S

Automatic mode T3S


Image processing - flow chart



About Piséo

• Independent Innovation Center specializing in the design, realization and characterization of illumination,detection and imaging systems integrating advanced photonic technologies (LED, VCSEL, laser diodes,spectrometers, image sensors, lidar, phosphors , optical materials ...).

• Supports companies in all sectors of activity in their innovation and optimization initiatives.

• Experience gained from large industrial groups.

• Created in November 2011 as part of the French State Call for Projects for shared innovation platforms.

• 21 industrial shareholders including GIL-Syndicat du luminaire, Yole Développement, Syndicat de l’éclairage,Serma, Cluster Lumière.

• Based in Lyon, France.

• 150+ clients (Large groups, ETI, SMEs, Start-ups)

• CIR, CII, and EASYTECH approved.

• 12 people


Our markets

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Our services


System design and Realization

• Application requirements of

photonic systems (UV, VIS, IR)

• Concept generation

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and software design

• Simulations

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• System integration

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small volumes production with

partners

• Redesign to cost, to quality

• Design for reliability

Test lab

• Photometric and colorimetric

measurements (accredited)

• Spectral and radiometric

measurements (UV, VIS, IR)

• Photobiological risk assessment

(accredited)

• Luminance and color maps of

displays, light panels, etc.…

• Electrical measurements

• Temperature measurements

• Characterization of cameras,

modules and imaging sensors

(VIS, IR): NUC, NETD,

responsiveness, MTF ...)

Application and technical

analyses

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components and systems

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component and systems

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reports of photonic components

and systems

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and systems performances and

construction

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➢ Integrating spheres Instrument Systems 2m & GL Optik 50cm

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What characterizes us

• 200+ customer projects and 4000+ tests carried out.

• Unique combination of expertise and high-level technical means in the design andcharacterization of illumination, detection and imaging systems.

• Very diverse industrial experience.

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Contact

Joël ThoméGeneral ManagerTel: +33 (0) 668 624 [email protected]

4, rue de l’Arsenal69200 VénissieuxFrance


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iRAY T3S Thermal Camera Performance Analysis - piseo.fr