The Cyprus Institute

About: The Cyprus Institute is a other organization based out in Nicosia, Cyprus. It is known for research contribution in the topics: Aerosol & Environmental science. The organization has 418 authors who have published 1252 publications receiving 32586 citations.

Multidimensional image retargeting

Abstract: Retargeting refers to the process by which an image or video is adapted from the display device for which it was meant (target display) to another one (retarget display). The retarget display has different features from the target one such as dynamic range, discretization levels, color gamut, multi-view, and refresh rate spatial resolution. This is a very relevant topic in graphics, given the increasing number of display devices from large, high-contrast screens to small cell phones with limited dynamic range; a lot of techniques are being published in different venues, and it's hard to keep up. For most cases retargeting can be an ill-posed problem, for example in the process of displaying Low Dynamic Range (LDR) or 8-bit content on High Dynamic Range (HDR) displays. Such a problem requires the retargeting algorithm to generate new content which is missing in the input image/frame. In this course, we will present the latest solutions and techniques for retargeting images along various dimensions such as dynamic range, colors, temporal and spatial resolutions, and for the first time offer a much-needed holistic view of the field. Moreover, we are going to show how to measure and analyze the changes applied to an image or video in terms of quality using both psychophysical experiments (subjective) and computational metrics (objective). The course should be of interest to anyone involved in graphics in a broader sense, given the almost unavoidable need to retarget results to different devices -from developers interested in implementing retargeting techniques, to users that just need an overall perspective. For researchers fully engaged in developing multi-dimensional retargeting techniques, this course will serve as a solid background for future algorithms.

Color Correction for Tone Reproduction

Abstract: High dynamic range images require tone reproduction to match the range of values to the capabilities of the display. For computational reasons as well as absence of fully calibrated imagery, rudimentary color reproduction is often added as a postprocessing step rather than integrated into the tone reproduction algorithm. However, in the general case this currently requires manual parameter tuning, although for some global tone reproduction operators, parameter settings can be inferred from the tone curve. We present a novel and fully automatic saturation correction technique, suitable for any tone reproduction operator, which exhibits better color reproduction than the state-ofthe-art and we validate its comparative effectiveness through psychophysical experimentation. Introduction Recent advances in both capture and display technologies allow images of a much wider dynamic range to be photographed, manipulated and displayed, better capturing the light of natural scenes and giving artists unparalleled freedom. Unlike prevalent consumer imaging pipelines though, no high dynamic range (HDR) standard has yet emerged defining the precise range, format or encoding to be used. As such, HDR data often needs to be compressed for display on most current displays, a process known as tonemapping [15, 2]. The aim of this paper is to preserve the appearance and information content of the image as much as possible while ensuring that it can be displayed on the chosen display device. To achieve that, tonemapping algorithms typically operate on the luminance of the image with little to no consideration for the color information present, leading to noticeable changes in the color appearance of the image, as shown in Figure 1. Commonly, tone compressed images acquire an over-saturated appearance when only the luminance channel is processed [12, 18]. Image appearance models, which can be seen as tone reproduction operators with integrated color appearance management [7, 9, 16], aim to reproduce color appearance, but they are designed with calibrated applications in mind and often come at the cost of higher computational complexity due to spatially varying processing. Despite their accuracy, these factors can limit their general applicability. Some solutions exist for correcting saturation mismatches after tone reproduction [12, 18]. This leads to computationally efficient correction, although we have observed that existing methods tend to create hue and luminance artefacts. Moreover, they require manual parameter selection which is strongly image and tone reproduction operator dependent. Recently, a psychophysical study was conducted for defining an automatic model to derive the parameters necessary for such corrections, but only allows parameters to be predicted when the tone compression or expansion function is global [12]. Instead, we propose a new approach for correcting saturation mismatches after dynamic range compression. We base our algorithm on insights from color science and on the observation that the amount of desaturation can be inferred from the non-linearity applied by the tone curve, irrespective of whether the tone reproduction operator was spatially varying or not. As such, our approach is parameter-free and agnostic to the operator used for mapping the dynamic range of the image or video. We find that our algorithm reproduces saturation significantly better than the current state-of-the-art. Related Work Differences in viewing conditions may result in significant mismatches in perceived color, which can be attributed to idiosyncrasies of the human visual system. To ensure that the appearance of a scene is correctly reproduced on a display, many issues will have to be taken into account, all broadly belonging to the field of color reproduction [8]. Image appearance models can be used to reproduce images as a human observer would see them under given viewing conditions [5, 16]. Such algorithms can be configured to yield calibrated color reproduction, and therefore do not require color post-processing. However, measurements of scene and display conditions are needed as inputs to image appearance models so that the human visual response can be accurately predicted. This requires specialist equipment such as photometers. These algorithms also tend to be computationally expensive, further limiting their use to offline processing. Dynamic range mismatches between scenes and display devices are therefore typically handled by tone reproduction operators. In essence, most of these algorithms focus on one dimension of the color gamut, namely compression along the luminance direction [15, 2]. Appearance effects are often ignored, leading to images which may appear too saturated. This problem can be mitigated by combining tone reproduction and color appearance algorithms [1]. However, this solution still requires calibrated data and measured viewing conditions to drive the color appearance component. A more common approach to saturation reproduction is to post-process the tone-mapped image, manually adjusting saturation to levels that appear plausible. Perhaps the most well-known technique for color correction involves the adjustment of color values by means of a power function, according to user parameter p ∈ [0,1] [18]. Given an original high dynamic range imTonemapped with Li et al. 2005 Corrected saturation reduced Corrected saturation enhanced Tonemapped with Reinhard et al. 2012 Figure 1. The same HDR image was tonemapped with different operators (left [10], right [16]). The left tonemapped image is overly saturated, while the tonemapping algorithm used on the right has reduced the saturation too far. With our method, both images are automatically corrected to have a very similar appearance by considering their relation with the original HDR image. (Source image from Mark Fairchild’s HDR Survey) age with input pixels Mo = (Ro,Go,Bo) specified in some linear RGB color space, and its associated per-pixel luminances Lo, it is first tonemapped with an operator f () that modifies the image’s luminances, Lt = f (Lo). The color-corrected image Mc is then produced with:

Impact of mineral dust on cloud formation in a Saharan outflow region

Abstract: . We present a numerical modelling study investigating the impact of mineral dust on cloud formation over the Eastern Mediterranean for two case studies: (i) 25 September 2008 and (ii) 28/29 January 2003. In both cases dust plumes crossed the Mediterranean and interacted with clouds forming along frontal systems. For our investigation we used the fully online coupled model WRF-chem. The results show that increased aerosol concentrations due to the presence of mineral dust can enhance the formation of ice crystals. This leads to slight shifts of the spatial and temporal precipitation patterns compared to scenarios where dust was not considered to act as ice nuclei. However, the total amount of precipitation did not change significantly. The only exception occurred when dust entered into an area of orographic ascent, causing glaciation of the clouds, leading to a local enhancement of rainfall. The impact of dust particles acting as giant cloud condensation nuclei on precipitation formation was found to be small. Based on our simulations the contribution of dust to the CCN population is potentially significant only for warm phase clouds. Nevertheless, the dust-induced differences in the microphysical structure of the clouds can contribute to a significant radiative forcing, which is important from a climate perspective.

Driving parameters of biogenic volatile organic compounds and consequences on new particle formation observed at an eastern Mediterranean background site

Abstract: . As a part of the Chemistry-Aerosol Mediterranean Experiment (ChArMEx) and Cyprus Aerosols and Gas Precursors (ENVI-Med CyAr) programs, this study aims primarily to provide an improved understanding of the sources and the fate of volatile organic compounds (VOCs) in the eastern Mediterranean. More than 60 VOCs, including biogenic species (isoprene and eight monoterpenes) and oxygenated VOCs, were measured during a 1-month intensive field campaign performed in March 2015 at the Cyprus Atmospheric Observatory (CAO), a regional background site in Cyprus. VOC measurements were conducted using complementary online and offline techniques. Biogenic VOCs (BVOCs) were principally imputed to local sources and characterized by compound-specific daily cycles such as diurnal maximum for isoprene and nocturnal maximum for α - and β -pinenes, in connection with the variability of emission sources. The simultaneous study of pinene and isoprene temporal evolution and meteorological parameters has shown that BVOC emissions were mainly controlled by ambient temperature, precipitation and relative humidity. It was found that isoprene daytime emissions at CAO depended on temperature and solar radiation changes, whereas nocturnal BVOC concentrations (e.g., from oak and pine forests) were more prone to the relative humidity and temperature changes. Significant changes in monoterpene mixing ratios occurred during and after rainfall. The second part of the study focused on new particle formation (NPF) events at CAO. BVOCs are known to potentially play a role in the growth as well as in the early stages of formation of new atmospheric particles. Based on observations of the particle size distribution performed with a differential mobility particle sizer (DMPS) and the total number concentrations of particles larger than 1 nm diameter measured by particle size magnifier (PSM), NPF events were found on 14 out of 20 days of the field campaign. For all possible proxy parameters (meteorological parameters, calculated H2SO4 and measured gaseous compounds) having a role in NPF, we present daily variations of different classes during nucleation event and non-event days. NPF can occur at various condensational sink (CS) values and both under polluted and clean atmospheric conditions. High H2SO4 concentrations coupled with high BVOC concentrations seemed to be one of the most favorable conditions to observe NPF at CAO in March 2015. NPF event days were characterized by either (1) a predominant anthropogenic influence (high concentrations of anthropogenic source tracers observed), (2) a predominant biogenic influence (high BVOC concentrations coupled with low anthropogenic tracer concentrations), (3) a mixed influence (high BVOC concentrations coupled with high anthropogenic tracer concentrations) and (4) a marine influence (both low BVOC and anthropogenic tracer concentrations). More pronounced NPF events were identified during mixed anthropogenic–biogenic conditions compared to the pure anthropogenic or biogenic ones, for the same levels of precursors. Analysis of a specific NPF period of the mixed influence type highlighted that BVOC interactions with anthropogenic compounds enhanced nucleation formation and growth of newly formed particles. During this period, the nucleation-mode particles may be formed by the combination of high H2SO4 and isoprene amounts, under favorable meteorological conditions (high temperature and solar radiation and low relative humidity) along with low CS. During the daytime, growth of the newly formed particles, not only sulfate but also oxygen-like organic aerosol (OOA) mass contributions, increased in the particle phase. High BVOC concentrations were observed during the night following NPF events, accompanied by an increase in CS and in semi-volatile OOA contributions, suggesting further BVOC contribution to aerosol nighttime growth by condensing onto pre-existing aerosols.