Karakterizacija fotografskih svetlobnih virov in nastavkov za oblikovanje svetlobe

Štampfl, Veronika (avtor), Ahtik, Jure (mentor)

Doktorska disertacija se osredotoča na celostno karakterizacijo svetlobe, ki jo emitira svetlobni vir, bodisi z ali brez dodanega nastavka za oblikovanje svetlobe. Ti so pogosto uporabljeni pri osvetljevanju različnih fotografskih scen, njihov namen pa je preoblikovati svetlobo na različne načine – usmeriti, razpršiti, obarvati ali spremeniti njeno jakost. V namen kvantitativne karakterizacije teh sprememb smo v seriji petih raziskav razvili novo metodo, ki opiše razlike v ostrini svetlobe ter tako dopolni nabor standardiziranih metod za opisovanje preostalih lastnosti. V prvi raziskavi smo preverili vpliv okolice na svetlobne lastnosti fotografske scene ter s tem določili parametre testnega okolja, ki bodo dovoljevali opazovanje testne svetlobe brez drugih vplivov. Kot najprimernejši okolji smo določili fotografsko temnico in fotografski studio s črno okolico. V drugi in tretji raziskavi smo zasnovali standardno testno sceno, ki zajema projekcijsko površino in objekt za generiranje senc. Osredotočili smo se na svetlostne parametre površin obeh delov, na projekcijski površini pa vzpostavili pogoje, ki dovoljujejo registracijo oziroma poravnavo ploskovnih fotografij površine. Slednje smo dosegli z uporabo ArUco oznak in prilagoditvijo odprtokodnih knjižnic za njihovo zaznavo. V četrti raziskavi smo zasnovali metodo, ki kvantitativno določi ostrino svetlobe. Temelji na slikovnih analizah senc, ki jih na standardni testni sceni generira posamezen svetlobni vir. Z upragovljanjem slike sence pri vsakem pragu ter določanjem težišča oblike upragovljane sence pridobimo niz koordinat, ki v koordinatnem sistemu izriše podobo sence. Nizom podatkov nato določimo točke sprememb, ki opredeljujejo območja polne sence in polsence oziroma umbre in penumbre. Segmentiranim sencam nato določimo njihove lastnosti, kot sta višina polne sence in širina polsence, razmerje med vrednostma pa opisuje končno oceno ostrine svetlobe, ki jo označujemo s H in nima enote. Metodo nato v peti raziskavi nadgradimo in z njeno popolno avtomatizacijo odpravimo pomanjkljivosti. Pri tem analiziramo nabor raznolikih nastavkov za oblikovanje svetlobe in proučimo njihov vpliv na spremembe v kakovosti barvne reprodukcije ter ostrine izvornega svetlobnega snopa. Glavni cilj doktorske disertacije je z vzpostavitvijo metode za kvantitativen opis ostrine svetlobe dosežen, v procesu raziskav pa opredelimo nove smernice za nadaljnje raziskave. Izkaže se, da je analiza senc tudi v nadzorovanem okolju kompleksna, na njihov nastanek pa vpliva širok razpon lastnosti materialov, s katerimi pride v stik izvorna svetloba. Tako usmerimo nadaljnje raziskovanje v interdisciplinarni pristop, ki bo omogočal natančnejšo analizo materialov.

• Jezik: Slovenski jezik
• Ključne besede: fotografija, ostrina svetlobe, senca, nastavki za oblikovanje svetlobe, slikovna analiza
• Vrsta gradiva: Doktorsko delo/naloga
• Organizacija: NTF - Naravoslovnotehniška fakulteta
• Leto izida: 2025
• PID: 20.500.12556/RUL-170610
• Datum objave v RUL: 10.07.2025

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: Characterization of photographic light sources and light shaping attachments

Izvleček

The dissertation focuses on the comprehensive characterisation of the light emitted by a light source, either with or without an additional light-shaping attachment. These attachments are commonly used in the illumination of various photographic scenes and serve to modify the light in different ways – directing it, scattering it, colouring it or changing its intensity. In order to characterise these changes quantitatively, we have developed a new method in a series of five studies that describes the differences in light harshness and thus complements the range of standardised methods for describing the other properties. In the first study, we investigated the influence of the environment on the light properties of the photographic scene and determined the parameters that allow the test light to be observed without other influences. We defined the photographic darkroom and the photo studio with a black environment as the most suitable environments. In the second and third studies, we designed a standard test scene with a projection surface and an object that creates shadows – an occluder. We focussed on the brightness parameters of the surfaces of both parts and created conditions on the projection surface that allowed the registration of surface photographs. This was achieved by using ArUco markers and modifying open source libraries to recognise them. In the fourth study, we developed a method for the quantitative determination of light harshness. This method is based on image analysis of shadows generated by a single light source on the standard test scene. By thresholding the shadow image and determining the centre of gravity of the shadow shape, we obtain a set of coordinates that draw the shape of the shadow. Using this data set, we identify points of change that define the areas of umbra and penumbra, while the ratio of their properties describes the final harshness of the light. In the fifth study, we improved this method and eliminated weaknesses by fully automating the process. We analysed a number of different light-shaping attachments and investigated their effects on the changes in colour rendering quality and the harshness of the light beam. The main objective of the thesis is to develop a method to quantitatively describe the harshness of light. However, in the course of the research we are defining new directions for further studies. It has been shown that analysing shadows even in a controlled environment is complex and their shape is influenced by a variety of material properties that the light beam comes into contact with. Therefore, we are focussing further research on an interdisciplinary approach that would allow a more comprehensive material analysis.

• Ključne besede: photography, light harshness, shadow, light-shaping attachments, image analysis