Bachelor Thesis

Defective Pixel Correction of an

IR-camera-module

executed at

Carinthian Tech Institute

School of electronics

in cooperation with

Active Photonics AG

by

Andreas Blassnig

Villach, June 2009

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Summary

Kurzfassung

Summary

This paper deals with the substitution of defective sensor pixels regarding an

Infrared Energy (IR) camera module. The work includes information about

the development of algorithms and the optimization regarding hardware usage

of a Field Programmable Gate Array (FPGA). Furthermore, the work outlines

the test of the algorithms with the aid of Matrix Laboratory (Matlab) and the

implementation in Very high speed integrated circuit Hardware Description

Language (VHDL). Simulations of the VHDL module conclude the work.

Keywords: Dead Pixel, FPGA, Infrared Sensor, VHDL

Kurzfassung

Diese Arbeit befasst sich mit der Substitution defekter Sensor-Pixel, ein Infrarot-

Kamerasystem betreend. Neben der Entwicklung von Algorithmen, wird

auch auf deren Optimierung, den Hardware-Aufwand in einem FPGA betref-

fend, eingegangen. Weiters wird der Test der Algorithmen mithilfe von Matlab

vorgestellt und auf die VHDL-Implementierung eingegangen. Die Simulation

des VHDL Modules bildet den Abschluss der vorliegenden Arbeit.

Suchbegrie: Dead Pixel, FPGA, Infrarotsensor, VHDL

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Contents

Contents

Contents

3

Preface

4

1 Task

6

2 Realization

8

2.1 Denition of defective Pixels .

8

2.1.1 Types of defects concerning monolithic pyroelectric arrays 8

2.1.2 Types of defects concerning microbolometer technology .

9

2.2 Substitution algorithms .

9

2.2.1 Single pixel substitution 10

2.2.2 Cluster error correction 14

2.2.3 Row and column errors 16

2.3 Tests with Matlab 18

2.3.1 Import of test pictures 18

2.3.2 Correction and display of test pictures 19

2.4 VHDL programming 26

2.4.1 Entity declaration and data transfer 28

2.4.2 Memory management 29

2.4.3 Implementation of algorithms 30

2.4.4 Simulation and tests 33

3 Conclusion

36

3.1 Findings 36

3.2 Outlook 37

Figures

39

Listings

41

List of abbreviations

42

Bibliography

43

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Preface

Preface

Active Photonics AG works on thermal imaging systems. In order to enhance

the market position, the development of a complete IR camera system, from

the sensor to the display, was initiated. The whole system should be a single

chip solution, running on an FPGA. The following gure 0.1 shall demonstrate

the modules necessary to realize the task.

x

x

x

x

x

x

Figure 0.1: Overview of the whole system

The system will run on an FPGA, which will be of the order of a XILINX

Spartan-3A DSP XC3SD3400A. The chip provides a sucient amount of logic

cells and distributed Random Access Memory (RAM) - as well as block RAM

bits. On this account the idea of a system without the need of a external RAM

chip emerged. The matter of fact, that the algorithms which are fullling the

tasks of the individual modules (see gure 0.1), will run on an FPGA, should

be regarded in the design process. The more complex the algorithms are, the

more hardware (Congurable Logic Blocks (CLB′s), Look Up Tables (LUT′s)

etc.) is required. The dead pixel substitution module (see gure 0.1) is topic

of this paper. It serves as interface between the oset- and gain-correction

module and the image scaling block. The purpose of the defective pixel module

is to substitute degraded sensor elements. Due to the fact that the sensor

(ULIS Long-Wave InfraRed (LWIR) uncooled microbolometer) which should

be employed, is not available in the rst phase of the development process,

the data format, timing, resolution and the serial conguration interface of

the sensor was emulated by the use of a KITE pyroelectric sensor (see section

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Preface

2.4 and gure 2.28 for the block diagram of the sensor emulator). Figure 0.2

illustrates the hardware which was worked with.

Figure 0.2: Hardware view of the camera module

The sensor construction, including the optics, can be seen in the image above

to the left. The data is analyzed and processed by using a XILINX Spartan3

XA3S1000 evaluation board, adapted for the application (see gure 0.2 to the

right).

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CHAPTER 1. TASK

1 Task

The electromagnetic spectrum is divided into three segments by wavelength,

which is measured in microns (1/1,000,000 of a meter) [12].

1. 0.76 to 1.5 microns = near infrared

2. 1.5 to 5.6 microns = middle infrared

3. 5.6 to 1000 microns = far infrared

Figure 1.1: IR wavelength diagram

This wavelength (highlighted in gure 1.1) of light warms objects without

warming the air between the source and the object. Radiant heat can also

be called IR. Infrared waves are not visible to human eyes but can be seen by

special instruments that translate infrared into colors that are visible to our

eyes. Section 2.1.1 and 2.1.2 give a review of infrared sensors.

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CHAPTER 1. TASK

Dead elements, meaning defective sensor pixels, may interfere images remark-

able. In order to avoid these negative eects on the image quality, substi-

tution algorithms have to be designed. Infrared camera systems, valid for

microbolometer sensors as for pyroelectric sensors, suer from dead elements.

The avoidance of these impairments is an important issue for all imaging sys-

tems. The development of algorithms, in order to substitute degraded pixels,

is an important aair. An approach to a solution is the replacement of the

unwanted values with values derived from "good" pixels in the vicinity of the

"bad" ones (see section 2.2).

Figure 1.2: Infrared Image containing defective pixels

Figure 1.2 shows an IR image containing defective pixels. As can be seen, the

image quality is interfered by the dead elements.

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