I. Budimir, N. Mrvac, M. Matijević Utjecaj debljine rešetke kod Munker-Whiteovog efekta ISSN 1330-3651 (Print), ISSN 1848-6339 (Online) DOI: 10.17559/TV-20140821220932 THE INFLUENCE OF THE THICKNESS OF THE GRID IN MUNKER-WHITE EFFECT Ivan Budimir, Nikola Mrvac, Mile Matijević Original scientific paper This paper shows the influence of the thickness of the grid on the intensity and assimilation in Munker-White effect. It can be described as the effect of assimilation of grey rectangular elements into the colour of unbroken lines. They are perceived darker in combination with grey and black lines, and lighter in white and grey combination. Measured colorimetric differences are shown in CIEDE2000 system. Three polynomial statistical regression models were created based on the results. Models contain polynomial expressions describing the influence of the grid thickness on the intensity shift of rectangular objects in Munker-White effect. Models were tested statistically and the analysis of measured parameters shows their statistical representativeness. Keywords: assimilation; mathematical model; Munker-White; regression analysis; simultaneous contrast Utjecaj debljine rešetke kod Munker-Whiteovog efekta Izvorni znanstveni članak U radu je opisan utjecaj debljine rešetke na intenzitet simultanog kontrasta i asimilacije kod Munker-Whiteove efekta. Isti možemo opisati kao pojavu gdje se sivi elementi (pravokutni elementi) asimiliraju s bojom neprekinutih linija, koje se u kombinaciji sa sivo-crnim linijama percipiraju tamnije, a sa sivo-bijelim linijama svjetlije. Dobivene kolorimetrijske razlike prikazane su u CIEDE2000 sustavu. Na temelju rezultata napravljena su tri polinomijalna statistička regresijska modela. Modeli sadrže polinomijalne izraze koji opisuju utjecaj debljine rešetke na intenzitet pomaka pojavnosti svjetline pravokutnih elemenata kod Munker-Whiteovog efekta. Modeli su statistički testirani te je analizom dobivenih parametara pokazano da su statistički reprezentativni. Ključne riječi: asimilacija; matematički model; Munker-White; regresijska analiza; simultani kontrast 1 Introduction While attempting to analyse the psychophysical visual effect shown in the design of Susan Hirth [1] Michael White designed in 1979 a brand new black and white grid structure known as Munker-White illusion [2]. Today it is known as the strongest illusion of whiteness [4] and it connects psychophysical effect of simultaneous contrast and assimilation. Simultaneous contrast is the psychophysical effect which causes the shift of colour appearance in response to the colour change of the background. Munker-White illusion contains grey rectangular elements that are assimilated into the parallel coloured lines [2, 3, 4]. Fig. 1 shows the change between grey elements and black and white lines. Grey rectangular elements appear darker in combination with grey and black lines. They appear lighter in combination with grey and white lines. This effect has been and is the object of numerous scientific researches. Research of Munker-White and other psychophysical effects is often interdisciplinary and involves different research scientific areas such as graphic technology, psychology, medicine, neurology and math. Figure 1 Munker - White effect The structure of Munker-White effect contains the composition of parallel lines with rectangular elements placed in between (Fig. 1, left) and within (Fig. 1, right). The structure is universal and is often found in graphic arts and different types of design [5]. The influence of Munker-White effect on graphic reproductions is intensively studied [6, 7]. Gained results allow more efficient control of colour information and better use of Munker-White effect in graphic design. A series of mathematical models were developed in order to describe the appearance of psychophysical visual effects including the Munker-White effect. Most of the models come from the so-called DOG rule (Difference of Gaussian) [8]. DOG is a mathematical algorithm based on Gauss filters. Gauss filters do not allow areas of high contrast. Some new mathematical models explain the shift of lightness perception with neural filters for processing spatial frequency information and orientation of contrast. Munker-White effect is best described by filters sensitive to contrast direction according to so-called ODOG rule (Oriented Difference of Gaussian) [9, 10]. Lately, there have been attempts to define unique mathematical theory for description of different psychophysical effects including Munker-White effects. It was determined that a measurement scale of two dimensional interval differences of Gauss filter [11] can be made. It represents the mathematical model for common description of chromatic simultaneous contrast and assimilation for description of Munker-White effect. The purpose of this paper is to describe and research the scale of influence on perception by Munker-White effect in order to add to the unique mathematical theory for description of psychophysical effects. The application of gained results will enable more efficient usage of this psychophysical effect in different media, therefore enhancing the quality of graphic product. Tehnički vjesnik 22, 2(2015), 425-430 425