Lidija Mandić

Discrete Fourier transform–based watermarking method with an optimal implementation radius

In this paper, we evaluate the degradation of an image due to the implementation of a watermark in the frequency domain of the image. As a result, a watermarking method, which minimizes the impact of the watermark implementation on the overall quality of an image, is developed. The watermark is embedded in magnitudes of the Fourier transform. A peak signal-to-noise ratio is used to evaluate quality degradation. The obtained results were used to develop a watermarking strategy that chooses the optimal radius of the implementation to minimize quality degradation. The robustness of the proposed method was evaluated on the dataset of 1000 images. Detection rates and receiver operating characteristic performance showed considerable robustness against the print-scan process, print-cam process, amplitude modulated, halftoning, and attacks from the StirMark benchmark software.

Comparison of Color Difference Equations

Advanced color difference equations still do not necessarily predict accurately the color differences for complex stimuli such as photographic images. The CIELAB color-difference formula has been used extensively for quality control in industry but its application is limited because CIELAB space is still far from being perceptually perfectly uniform. The consequence of this is that for equal perceptual color differences, the values of CIELAB color differences can vary by an order of magnitude. The aim of this work is to compare accuracy of three color difference equations that are recently used

CATV broadband technologies

Cable television systems can be successfully used as broadband multimedia networks. Cable TV providers can offer additional services over CATV network, such as Internet access, video on demand and other applications. The article describes different techniques and technologies applied in modern two-way interactive CATV systems that enable variety of new service.

Copyright protection of images on a social network

In this paper we developed a steganographic method for image protection on Facebook social network. The method hides additional information such as a logo or serial number. Uploading the images on the social network has induced image degradation on the original images. Based on the analysis of this attack we developed a method based on the discrete cosine transform - DCT where additional information is hidden by modifying the coefficients in the cosine domain. The method was evaluated and it is shown that bit error rate (BER) for different attacks was below 1%.

Data formats in digital prepress technology

The printing industry is on its way to become a multimedia industry. Printing will not be the only media and means of outputting information. Printed products and online media have a common prepress stage (premedia) which only diverges just before the functional output as electronic media or as printed media. A good example of the potential of the multimedia market is the use of efficient workflow. The data file can be directly transmitted to different media by efficient workflow. Thanks to digital technology, all captured text and image data can be used for multimedia purposes. An incorrect data format can affect the quality of a prepress product. The aim of this article is to discuss the most prevalent data formats used in open prepress systems.

Corresponding colors: visual and predictive data

In cross-media color reproduction, it is important to be able to predict the colors under different viewing conditions. The two commonly used media, CRT displays and printed images were included in psychophysical experiments using six complex images. The experiments were carried out in dark and average surround. We have compared corresponding colors obtained from experiments with corresponding colors predicted with the use of two color appearance models, CIECAM97s and CIECAM02.

Applicability of the GCR masking in an image watermarking method

There exist continuous effort to develop new or improve existing watermarking methods. The main goal of this paper is to give preliminary insight of the applicability of the Gray Component Replacement (GCR) masking to frequency domain based watermarking scheme. The use of GCR masking can potentially increase the performance of a watermarking method by improving robustness or imperceptibility of an embedded watermark. The applicability of GCR masking is tested by extending well known watermarking method with GCR masking capability and comparing the imperceptibility of the embedded watermark before and after GCR masking. Results show that GCR masking can substantially increase the PSNR value of the watermarked image.

Adjustment of visual information for visually impaired people

The aim of this work is to test algorithms for image enhancement with different values in the algorithm and to test those algorithms on the different accelerators that could be used for medical aids. The results of this research show advantages and disadvantages of equipment that we used and also can indicate implantation of algorithm into portable devices. Five selected images were filtered through proposed algorithm and compared with golden standard through metrics MSE, PSNR and SSIM. Speeup for edge detector was tested on different machines.

Developing a custom colour target for artwork imaging

Abstract When characterising digital camera for capturing art paintings, the standard targets are often used, resulting in unacceptable differences in reproducing some special colours, so additional time must be spent for visual editing and colour adjusting in various software applications. To avoid the need for excessive colour editing, and to improve workflow efficiency and colour accuracy, the special colour reference target for digital camera characterisation was developed, applied and tested in these research. The object of digitalisation was paintings made with gouache paint, so two custom gouache reference targets with different numbers of colour samples (named CGRT24 and CGRT96) were created for digital camera colour characterisation. The main criteria for construction of targets were defined, as the optimal studio conditions for digital image capture of art paintings. By analysing the results gained with profiles testing, it was established that the errors in colour reproduction, which appear when using the standard targets (GretagMacbeth ColorChecker and ColorChecker DC) was decreased when using the developed CGRT targets for digital camera characterisation. Also, it was found out that the larger number of colour samples on target does not guarantee the more accurate camera profile. The results show that the colorimetric properties of colour samples are more important than the number of samples and proves that there is a benefit of developing the custom target tailored to the specific need.

The Model of Degradation of Color Values in a Reproduction Process

This paper deals with the problem of the degradation of color information that happens when color image is converted from one medium to another. The purpose of experiment was to determine the behaviour between two closely related colors when transferred on paper and then digitalized back using scanner. The aim of research was to examine the possibility of information hiding by means of modification of RGB channels of a digital color image.