Camera System Performance Derived from Natural Scenes

The Modulation Transfer Function (MTF) is a well-established measure of camera system performance, commonly employed to characterize optical and image capture systems. It is a measure based on Linear System Theory; thus, its use relies on the assumption that the system is linear and stationary. This is not the case with modern-day camera systems that incorporate non-linear image signal processes (ISP) to improve the output image. Non-linearities result in variations in camera system performance, which are dependent upon the specific input signals. This paper discusses the development of a novel framework, designed to acquire MTFs directly from images of natural complex scenes, thus making the use of traditional test charts with set patterns redundant. The framework is based on extraction, characterization and classification of edges found within images of natural scenes. Scene derived performance measures aim to characterize non-linear image processes incorporated in modern cameras more faithfully. Further, they can produce ‘live’ performance measures, acquired directly from camera feeds

A power-saving modulation technique for time-of-flight range imaging sensors

Time-of-flight range imaging cameras measure distance and intensity simultaneously for every pixel in an image. With the continued advancement of the technology, a wide variety of new depth sensing applications are emerging; however a number of these potential applications have stringent electrical power constraints that are difficult to meet with the current state-of-the-art systems. Sensor gain modulation contributes a significant proportion of the total image sensor power consumption, and as higher spatial resolution range image sensors operating at higher modulation frequencies (to achieve better measurement precision) are developed, this proportion is likely to increase. The authors have developed a new sensor modulation technique using resonant circuit concepts that is more power efficient than the standard mode of operation. With a proof of principle system, a 93–96% reduction in modulation drive power was demonstrated across a range of modulation frequencies from 1–11 MHz. Finally, an evaluation of the range imaging performance revealed an improvement in measurement linearity in the resonant configuration due primarily to the more sinusoidal shape of the resonant electrical waveforms, while the average precision values were comparable between the standard and resonant operating modes

The Imaging Magnetograph eXperiment (IMaX) for the Sunrise balloon-borne solar observatory

The Imaging Magnetograph eXperiment (IMaX) is a spectropolarimeter built by four institutions in Spain that flew on board the Sunrise balloon-borne telesocope in June 2009 for almost six days over the Arctic Circle. As a polarimeter IMaX uses fast polarization modulation (based on the use of two liquid crystal retarders), real-time image accumulation, and dual beam polarimetry to reach polarization sensitivities of 0.1%. As a spectrograph, the instrument uses a LiNbO3 etalon in double pass and a narrow band pre-filter to achieve a spectral resolution of 85 mAA. IMaX uses the high Zeeman sensitive line of Fe I at 5250.2 AA and observes all four Stokes parameters at various points inside the spectral line. This allows vector magnetograms, Dopplergrams, and intensity frames to be produced that, after reconstruction, reach spatial resolutions in the 0.15-0.18 arcsec range over a 50x50 arcsec FOV. Time cadences vary between ten and 33 seconds, although the shortest one only includes longitudinal polarimetry. The spectral line is sampled in various ways depending on the applied observing mode, from just two points inside the line to 11 of them. All observing modes include one extra wavelength point in the nearby continuum. Gauss equivalent sensitivities are four Gauss for longitudinal fields and 80 Gauss for transverse fields per wavelength sample. The LOS velocities are estimated with statistical errors of the order of 5-40 m/s. The design, calibration and integration phases of the instrument, together with the implemented data reduction scheme are described in some detail.Comment: 17 figure

Ispitivanje parametara kvalitete snimki digitalnih kamera za potrebe fotogrametrijske izmjere primjenom bespilotnih letjelica

Nowadays, unmanned aircrafts are more frequently used for measurement purposes. Size of aircrafts is often proportional to its price and load. Aircraft load of 2–3 kg, as required to lift DSLR camera, lens and gimbal (camera stabilizer) in the air, are higher-priced (>50,000 kn). Those kinds of aircrafts have their limits within the law, but also practical limitations because of its size. With the development of autonomous small size cameras such as action cameras appeared the ability to use cheaper, smaller and unmanned aircrafts with lower load in photogrammetric purposes. Of course, to use such a camera in measuring purposes first it is necessary to carry out adequate calibration method and define the elements of internal orientation of the camera. It is important to emphasize that the geometric calibration, or the elimination of geometric errors in the mapping is the key precondition to create idealized images i.e. images of actual optical mapping. This paper researches the quality of content mapped on images with the purpose of investigating the possibility of using action cameras in measuring purposes. The study is based on objective indicators such as global statistical image quality parameters, Modulation Transfer Function and visual analysis of test field images. For the purpose of the paper a modified test field based on the ISO 12233 standard was developed and for the first time used.U današnje je vrijeme sve češća upotreba bespilotnih letjelica u mjerne svrhe. Veličina bespilotne letjelice često je proporcionalna cijeni i nosivosti. Letjelice nosivosti 2–3 kg, koliko je potrebno da se u zrak podigne DSLR kamera i objektiv te stabilizator kamere (engl. gimbal), višeg su cjenovnog razreda (>50000 kn). Takve letjelice imaju svoja ograničenja u zakonskim okvirima, ali i praktična ograničenja zbog svoje veličine. Razvojem autonomnih kamera malih dimenzija, kao što su akcijske kamere, pojavila se mogućnost korištenja jeftinijih, manjih te bespilotnih letjelica manje nosivosti u fotogrametrijske svrhe. Naravno, kako bi se takva kamera mogla koristiti u mjerne svrhe potrebno je prije svega provesti adekvatnu metodu kalibracije te definirati elemente unutarnje orijentacije kamere. Važno je naglasiti kako je geometrijska kalibracija, odnosno eliminacija geometrijskih pogrešaka u preslikavanju, ključan preduvjet u stvaranju idealizirane snimke, tj. snimke stvarnog optičkog preslikavanja. U ovom radu provedeno je ispitivanje kvalitete preslikanog sadržaja na snimke s ciljem ispitivanja mogućnosti korištenja akcijskih kamera u mjerne svrhe. Istraživanje se temelji na objektivnim pokazateljima kao što su globalni statistički parametri kvalitete snimki i modulacijska prijenosna funkcija te vizualna analiza snimki testnog polja. Za potrebe rada razvijeno je i po prvi puta korišteno modificirano testno polje temeljeno na normi ISO 12233

A high-finesse Fabry-Perot cavity with a frequency-doubled green laser for precision Compton polarimetry at Jefferson Lab

A high-finesse Fabry-Perot cavity with a frequency-doubled continuous wave green laser (532~nm) has been built and installed in Hall A of Jefferson Lab for high precision Compton polarimetry. The infrared (1064~nm) beam from a ytterbium-doped fiber amplifier seeded by a Nd:YAG nonplanar ring oscillator laser is frequency doubled in a single-pass periodically poled MgO:LiNbO$_{3}$ crystal. The maximum achieved green power at 5 W IR pump power is 1.74 W with a total conversion efficiency of 34.8\%. The green beam is injected into the optical resonant cavity and enhanced up to 3.7~kW with a corresponding enhancement of 3800. The polarization transfer function has been measured in order to determine the intra-cavity circular laser polarization within a measurement uncertainty of 0.7\%. The PREx experiment at Jefferson Lab used this system for the first time and achieved 1.0\% precision in polarization measurements of an electron beam with energy and current of 1.0~GeV and 50~$\mu$A.Comment: 20 pages, 22 figures, revised version of arXiv:1601.00251v1, submitted to NIM

Investigation of a new method for improving image resolution for camera tracking applications

Camera based systems have been a preferred choice in many motion tracking applications due to the ease of installation and the ability to work in unprepared environments. The concept of these systems is based on extracting image information (colour and shape properties) to detect the object location. However, the resolution of the image and the camera field-of- view (FOV) are two main factors that can restrict the tracking applications for which these systems can be used. Resolution can be addressed partially by using higher resolution cameras but this may not always be possible or cost effective. This research paper investigates a new method utilising averaging of offset images to improve the effective resolution using a standard camera. The initial results show that the minimum detectable position change of a tracked object could be improved by up to 4 times