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Öğe A Comparative Analysis of University Information Systems within the Scope of the Information Security Risks(Assoc Information Communication Technology Education & Science, 2016) Yilmaz, Rustu; Yalman, YildirayUniversities are the leading institutions that are the sources of educated human population who both produce information and ensure to develop new products and new services by using information effectively, and who are needed in every area. Therefore, universities are expected to be institutions where information and information management are used efficiently. In the present study, the topics such as infrastructure, operation, application, information, policy and human-based information security at universities were examined within the scope of the information security standards which are highly required and intended to be available at each university today, and then a comparative analysis was conducted specific to Turkey. Within the present study, the Microsoft Security Assessment Tool developed by Microsoft was used as the risk analysis tool. The analyses aim to enable the universities to compare their information systems with the information systems of other universities within the scope of the information security awareness, and to make suggestions in this regard.Öğe A histogram based image quality index(Wydawnictwo SIGMA - N O T Sp. z o.o. sekretariat@sigma-not.pl, 2012) Yalman, YildirayImage quality evaluation plays a very important role in any image processing application. A number of efforts have been made in the last decade to develop generalized image quality metrics. However, a common and easily applicable image quality measure is yet to be developed. In this paper, a new Histogram-based Image Quality Index (HQI) is proposed for use in place of traditional error summation methods. It can be calculated easily and performs significantly better than the widely used image distortion quality metric Mean Squared Error (MSE). A software release of the proposed image quality measure HQI and examples of its usage on different test images have been made available online: http://www.turgutozal.edu.tr/yyalman/contents/yyalman/files/HQI.zip. © 2020 Elsevier B.V., All rights reserved.Öğe A Histogram based Image Quality Index(Wydawnictwo Sigma-Not Sp Zoo, 2012) Yalman, YildirayImage quality evaluation plays a very important role in any image processing application. A number of efforts have been made in the last decade to develop generalized image quality metrics. However, a common and easily applicable image quality measure is yet to be developed. In this paper, a new Histogram-based Image Quality Index (HQI) is proposed for use in place of traditional error summation methods. It can be calculated easily and performs significantly better than the widely used image distortion quality metric Mean Squared Error (MSE). A software release of the proposed image quality measure HQI and examples of its usage on different test images have been made available online: http://www.turgutozal.edu.tr/yyalman/contents/yyalman/files/HQI.zip.Öğe A new color image quality measure based on YUV transformation and PSNR for human vision system(Tubitak Scientific & Technological Research Council Turkey, 2013) Yalman, Yildiray; Erturk, IsmailVarious methods for measuring perceptual image quality attempt to quantify the visibility of differences between an original digital image and its distorted version using a variety of known properties of the human vision system (HVS). In this paper, we propose a simple and effective full-reference color image quality measure (CQM) based on reversible luminance and chrominance (YUV) color transformation and peak signal-to-noise ratio (PSNR) measure. The main motivation of this new measure relies on a unique feature of the human eye response to the luminance and color. Experimental studies about the applicability of the CQM on a well-known test image under 6 different distortions, both perceivable by the human vision system and with the same PSNR value (i.e. 27.67), are presented. The CQM results are obtained as 39.56, 38.93, 38.08, 37.43, 37.10, and 36.79 dB for each distorted image, showing that image quality of the first image is noticeably higher than the others with respect to the same PSNR value. This conclusion attests that using the CQM together with the traditional PSNR approach provides distinguished results.Öğe A new full-reference image quality metric based on just noticeable difference(Elsevier, 2017) Toprak, Sevil; Yalman, YildirayAn Image Quality Metric (IQM) is used to measure how the image on which modifications are carried out is distorted. Knowing the distortion scale of the image is of significance for the intended purposes (compression, forensic, medical, etc.). The amount of distortion has different implications for each of the application and whether the image is convenient for the relevant application by using the IQM. One of the most basic approaches in the literature which is used in measuring the amount of the distortion is the Full-Reference Image Quality Metric (FR-IQM). The FR-IQM needs both the original and distorted image in the phase of comparison. In this study, taking into consideration the Human Vision System (HVS), a new full-reference image quality metric based on Just Noticeable Difference (JND) has been presented. Through this new metric, the HVS's physiological (color and light sensitivity) and psycho-physiological (texture and edge sensitivity) characteristics have been taken into consideration. Through the JND, the inclusion of the unintended modifications that cannot be sensed by the HVS has been prevented. The near-zero quality results point out the more quality image. The experimental results have showed that the metric in question demonstrates a higher level of performance for the HVS when compared with its counterparts.Öğe A Robust Watermarking Method for Mpeg-4 Based on Kurtosis(Oxford Univ Press, 2015) Yesilyurt, Murat; Yalman, Yildiray; Ozcerit, A. TuranWatermarking is a method of data hiding in relation to information security and copyright protection. In this paper, a new kurtosis-based watermarking approach is proposed for compressed video files. The proposed approach has two main parts. First, an intraframe of the video file is transformed from RGB to YCbCr color space and each Y component's kurtosis value is calculated. A threshold kurtosis value is determined for the video because it is recommended to interpret the kurtosis values in combination with noise and resolution measurement. Secondly, the middle band Discrete Cosine Transform (DCT) coefficients of the luminance (Y) component is used for watermarking processes considering the threshold kurtosis values. Each bit of the binary watermark is embedded in a different DCT block. The experimental results show that the proposed method can be safely used for watermarking processes when the point of interest is binary watermarks. In addition, the proposed watermarking approach is highly imperceptible and robust. Statistical and perceptual quality evaluations show that the proposed approach is better than its counterparts.Öğe Contemporary Approaches on No-Reference Image Quality Assessment Methods: A Comparative Study(Turgut Ozal Univ, 2012) Yalman, Yildiray; Guldogan, M. Burak; Sen, I. FerdiEven if many image quality assessment (IQA) methods have been proposed in literature, the poor standardization in the field of quality assessment and the lack of extensive and reliable comparisons of the performance of the different IQA often make the obtained results not very reliable. Basically, there are three IQA types in the literature called as full reference (FR-IQA), reduced reference (RR-IQA) and no reference (NR-IQA). NR-IQA has gained more importance in the last decade. In this paper we aim at comparing the existing NR-IQA methods in terms of quality results. Comparing results show that the current methods results are unrelated for the same images. This situation indicates that a standard should be determined for NR-IQA methods.Öğe Data hiding in digital images using a partial optimization technique based on the classical LSB method(Tubitak Scientific & Technological Research Council Turkey, 2013) Akar, Feyzi; Yalman, Yildiray; Varol, Huseyin SelcukThis paper presents a new partial optimization approach for the least significant bit (LSB) data hiding technique that can be used for protecting any secret information or data. A deterioration effect of as little as possible in an image is intended using the LSB data hiding technique and this is well realized utilizing the proposed partial optimization approach achieving the same data embedding bit rates. In the proposed approach, all of the image pixels are classified into 8 regions and then the 8 distinct ordering codings are applied to each region by the developed partial optimization encoder. Thus, the most effective outcome that has been obtained from the 8 regions means that the number of the altered bits is kept minimized Hence, the minimal values that have been attained from the 8 regions enable decoding that ensures relatively small distortions on the extracted cover image.Öğe Histogram based perceptual quality assessment method for color images(Elsevier, 2014) Yalman, YildirayA histogram based perceptual quality assessment (HPQA) method for color images is presented in this paper. Basically, the HPQA combines two quality assessment approaches (color image quality assessment and histogram based image quality assessment) and it uses the fourier transform. Its range is between 0 and 1.1 represents the best quality result, 0 represents the worst quality result for the HPQA. The HPQA results are more suitable than its counterparts in terms of the HVS and they can be obtained faster than-the other methods' results. In addition, it can easily differentiate effects of low distortions on color images. (C) 2014 Elsevier B.V. All rights reserved.Öğe Information Security Threats and Information Assurance(Assoc Information Communication Technology Education & Science, 2013) Yalman, Yildiray; Yesilyurt, MuratToday, the benefits of rapidly developing technology, as well as come to the fore the problems brought about. For this reason, individuals, institutions and organizations take measures to ensure the security of information. Information assurance is the practice of managing risks related to the use, processing, storage and transmission of information or data and the systems and processes used for those purposes. Thus, information security is now provided with information assurance measures. The presented work, especially in today's digital and networking technologies in order to ensure effective information security threats and describes the scope of what required for information assurance.Öğe Secret data embedding scheme modifying the frequency of occurrence of image brightness values(Springer India, 2014) Yalman, Yildiray; Erturk, IsmailThe main purpose of this presented work is to develop a data embedding method based on a new digital image histogram modification approach. The proposed scheme fundamentally is concerned about the frequency of occurrence of the image brightness values of the cover image for the data embedding procedures. The proposed scheme effectively realizes both perceptual invisibility and statistical invisibility so that obtained covered images are highly robust against common perceptual and statistical steganalysis techniques. The scheme provides reasonably higher payload values than its counterparts, as well as providing comparatively improved PSNR results.Öğe Security Threats on Mobile Devices and their Effects: Estimations for the Future(Nadia, 2016) Yesilyurt, Murat; Yalman, YildirayPortable devices are today used in all areas of life thanks to their ease of use as well as their applications with unique features. The increase in the number of users, however, also leads to an increase in security threats. This study examines the threats to mobile operating systems. Addressing the four mobile operating systems (Android, Apple OS (iOS), Symbian and Java ME) with the highest number of users, the study provides statistical information about the features of the corresponding operating systems and their areas of use. In the study, the most important threats faced by the mobile operating systems (Malware, Vulnerabilities, Attacks) and the risks posed by these threats were analyzed in chronological order and the future-oriented security perspective was suggested..Öğe Visual steganalysis of LSB-encoded audio data based on frequency domain characteristics(2013) Arslan, Yüksel; Yalman, YildiraySteganography is an art and science of information hiding. Text, audio and image files are usually used as cover data. Then, a secret message is embedded into these cover data that no one knows about it except sender and receiver. Mostly used methods for audio steganography are based on Least Significant Bit (LSB) method and its derivatives in the literature. Steganalysis is a methodology of detecting messages hidden using steganography. In this paper, a visual steganalysis method has been proposed. Secret text messages can be detected by using frequency domain characteristics of stego audio data which contain text messages. Experimental results show that if stego object contains text messages and it is encoded by LSB or its varieties, some remarkable changes can be observed in frequency domain characteristics and its spectrogram. Thanks to exploring these frequency domain characteristics of stego objects, steganalysis (stego text detection) on audio data can be visually realized. © 2014 Elsevier B.V., All rights reserved.
