Lithuanian Journal of Physics article / Lietuvos fizikos žurnalo straipsnis

IMPROVEMENT OF TERAHERTZ IMAGES BY ADAPTIVE DISCRETE COSINE TRANSFORM (DCT)-BASED DENOISING
Victoriya V. Abramova^a,b, Sergiy K. Abramov^a, Volodymyr V. Lukin^a, Ignas Grigelionis^b, Linas Minkevičius^b, and Gintaras Valušis^b
^aDepartment of Information-Communication Technologies, National Aerospace University, Chkalova 17, 61070 Kharkiv, Ukraine
^bDepartment of Optoelectronics, Center for Physical Sciences and Technology, Saulėtekio 3, 10257 Vilnius, Lithuania
Email: gintaras.valusis@ftmc.lt

Received 25 October 2022; accepted 28 October 2022

Due to certain hardware limitations the quality of terahertz images is often lower than desired, which makes it difficult to extract valuable information from them. The goal of this paper is to investigate possibilities to overcome some of these limitations by means of digital image processing. The research is held on a set of images obtained at different distances from the source of terahertz radiation at 0.1 THz frequency. It is shown that the noise in these images is mixed and has a significant level of spatial correlation. For image quality enhancement a fully automatic denoising method based on the use of a discrete cosine transform with a spatially adapted spectrum is proposed. It is shown that despite an initially low spatial resolution of terahertz images and intensive noise, it provides a good noise reduction with a good preservation of edges, which allows one to noticeably improve the quality of these images and make them more convenient for visual analysis carried out by a human operator.
Keywords: terahertz imaging, image denoising, correlated noise, DCT

TERAHERCINIŲ VAIZDŲ PAGERINIMAS NAUDOJANT DISKRETINE KOSINUSINE TRANSFORMACIJA PAREMTĄ TRIUKŠMO SUMAŽINIMO METODĄ
Victoriya V. Abramova^a,b, Sergiy K. Abramov^a, Volodymyr V. Lukin^a, Ignas Grigelionis^b, Linas Minkevičius^b, Gintaras Valušis^b

^aNacionalinio aerokosmoso universiteto Informacijos ir komunikacijos technologijų departamentas, Charkivas, Ukraina
^bFizinių ir technologijos mokslų centro Optoelektronikos skyrius, Vilnius, Lietuva

Žemą terahercinių (THz) vaizdų kokybę dažniausiai lemia aparatūriniai apribojimai, trukdantys naudingos informacijos vaizduose išskyrimui. Šio darbo tikslas buvo ištirti galimybes apeiti iškylančius apribojimus, pasitelkiant skaitmeninio vaizdų apdorojimo metodiką. Tyrimas atliktas naudojant vaizdų, užrašytų bandiniui esant skirtingu atstumu nuo 0,1 THz dažnio terahercinės spinduliuotės šaltinio, rinkinį. Darbe parodyta, kad gautuose THz vaizduose vyrauja kelių skirtingų prigimčių stipriai erdviškai koreliuotas triukšmas. Vaizdų kokybei pagerinti siūloma naudoti automatinį triukšmo sumažinimo metodą, paremtą diskretine kosinusine transformacija su erdviškai pritaikytu spektru. Parodoma, kad tokia metodika leidžia padidinti THz vaizdų kokybę efektyviai sumažinant pradinį triukšmą bei išsaugant ryškius vaizde esančių objektų kontūrus net ir esant žemai erdvinei skyrai ir dideliam pradiniam triukšmo lygiui, taip paruošiant vaizdus tolesnei vizualinei analizei.

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