We present a novel setup   in  which  real  objects  made  of two different materials can  be mixed  optically in a linearly weighted manner.  We conducted a psychophysical experiment in which observers rated optical mixtures of the three combinations of glossy, matte, and  velvety  green birds.  The observers rated the materials on four scales:  matte–glossy, hard–soft, cold–warm, and light-heavy. The judgments were found to be consistent and  varied  systematically with  the weights of the contributions. This record was migrated from the OpenDepot repository service in June, 2017 before shutting down

Koenderink, Jan J.

Pont, Sylvia C.

te Pas, Susan F.

van Doorn, Andrea  J.

Wijntjes, Maarten W.A.

English

ZENODO

Predicting Perceptions: Proceedings of the 3rd International Conference on Appearance, pp. 9-12, Edinburgh, UK, ISBN 978-1-4716-6869-2, April 2012. Perceptual Qualities of Optically Mixed Materials   Sylvia C. Pont  Perceptual Intelligence lab  Delft University of Technology  the Netherlands s.c.pont@tudelft.nl Andrea  J. van Doorn  Perceptual Intelligence  lab  Delft University of Technology  the Netherlands a.j.vandoorn@tudelft.nl Susan F. te Pas  Dept.  Social Sciences  Utrecht University  the Netherlands s.tepas@uu.nl   Maarten W.A. Wijntjes  Perceptual Intelligence lab  Delft University of Technology  the Netherlands m.w.a.wijntjes@tudelft.nl Jan J. Koenderink  Perceptual Intelligence lab  Delft University of Technology  the Netherlands jan.koenderink@telfort.nl      ABSTRACT We present a novel setup   in  which  real  objects  made  of two different materials can  be mixed  optically in a linearly weighted manner.  We conducted a psychophysical experiment in which observers rated optical mixtures of the three combinations of glossy, matte, and  velvety  green birds.  The observers rated the materials on four scales:  matte–glossy, hard–soft, cold–warm, and light-heavy. The judgments were found to be consistent and  varied  systematically with  the weights of the contributions.   Keywords Material perception, qualities, ecological optics, magic   1.   INTRODUCTION Natural materials cover  a  wide  range  of mutually  very different optical properties[1, 3].  However,  it has  been  suggested  that they  can  be  categorized into  roughly  a  dozen types of canonical modes  on the basis  of their bidirectional surface  scattering  or BRDF (for  this  paper  we do not con- sider  spatial  texture).  The  lobes  of the Bidirectional Re- flectance  Distribution  Function may  be  described by  their average direction, e.g.  in the illumination direction (backscattering  or retroreflection  [4]), roughly  in the specular  direc- tion (forward scattering or specular  reflection [3]), distributed over all directions (diffuse  scattering [3]), along  the surface (asperity scattering [3]) or perpendicular to it. This primary scattering direction is associated with  certain visual  characteristics  or modes  of material  appearance, for instance for- ward scattering with glossy-/shiny-/specularness and diffuse scattering with  matteness.  The  BRDF of generic  materials typically consist of several  of such lobes, e.g.  a peach  BRDF may contain a diffuse and a surface lobe, resulting in a com- bination of a matte and  a velvety mode.  Since the primary scattering direction is different for these  modes,  the salient features of the appearance modes usually  show up at differ- ent locations too.  Thus, similarly  to descriptions of BRDFs as linear  superpositions of scattering lobes, we can describe the appearance of 3D objects  consisting of any  materials as linear superpositions of 3D objects of different canonical ma- terials, e.g.  a glossy object as the superposition of a specular and  a matte object.  We are  particularly interested in the perception of mate- rial qualities that are important for interaction with objects. Karana [2] inventorized perceptual properties of materials that are important for interacting with  products.  She found the following list:  color intensity, colorfulness,  ductility, elasticity, glossiness,  hardness, odour,  reflectiveness, roughness, strength, transparency, warmth and lightness. In our experiment we will study  a selection of this list.   2.   EXPERIMENT  2.1   Methods We  made  a  setup  to optically mix  two  objects  in  a  lin- early  weighted manner, see figure  1.  It consists  of a black square  box with  30 cm ribs in which we put a vertical semi- transparent optical  mirror.  The  mirror  was  placed  diagonally  in the  box,  that is, at 45 degrees  with respect to  the viewing  direction. One of the objects was seen through the mirror.  The  other object was seen via the reflection  in the mirror.  The  objects were  lined  up  symmetrically with  respect  to  the  mirror  to  superpose them.   The  illumination apertures consisted of 6 cm by 6 cm square  openings  in the top of the box,  under  which  we affixed 6 cm long light baffles in order  to prevent light from one side of the  mirror  to reach  the object on the opposite  side.  The  box was put in a Ganzfeld  (fully diffuse light field).  The stimuli in the box are viewed by way of a 50 cm long 15 cm wide black  tube.  The stimuli  were  optical mixtures of three  objects of the  same shape but finished with different materials: birds with matte green  paint, with  glossy green  paint and  with a green  flock finish (the matte, glossy and  velvety  bird,  respectively), see figure 2.  The  green  color was matched via the  RAL system (the  matching is messed up in the photography, in the setup Predicting Perceptions: The 3rd International Conference on Appearance, 17-19 April, 2012, Edinburgh, UK. Conference Proceedings Publication ISBN: 978-1-4716-6869-2,  Pages: 9-12 @2012 Authors & Predicting Perceptions. All Rights Reserved.  Predicting Perceptions: Proceedings of the 3rd International Conference on Appearance, pp. 9-12, Edinburgh, UK, ISBN 978-1-4716-6869-2, April 2012.    Figure 1:  A  topview of  the inner part of  our setup. The setup consists of a box of 30x30x30cm, of which the inside is covered by black flocked paper.  A semi- transparent mirror was placed vertically at the diagonal of  the box - the reflection at the upper side of  the mirror is  clearly visible.  The red ellipse depicts the viewing hole in the box (since the setup is viewed through a tube made of  black flocked paper it was not visible in the photograph).   Figure 2:  The glossy (left), the velvety (centre), and the matte (right) birds.   the colors did match to the  human eye).  The  luminance of the two objects was  equalized;   to this  aim  we had  to  attenuate the  contribution from behind  the mirror  with  a 0.5 neutral density filter (NDF). The  weights  of the two contributions were varied  by way of NDFs of various  densities over the lighting openings  in the box.  We ran psychophysical experiments in the equalized  condition and with NDFs of 0.5, 1 and 2 (corresponding with attenuation factors of 3.16, 10 and 100, or “weights” of 0.32, 0.1 and  0.01, respectively), resulting in 7 weighted combinations for each of the three  material pairs.  Thus  we obtained 21 settings altogether. Participants did  three repeated ratings in randomized block  order.   The ratings were  collected  using  preprinted scales  representing the matte-glossy, hard-soft,  cold-warm and  light-heavy dimensions  on which the  observers could indicate their rating by drawing  a mark.   2.2   Results We  find very  consistent  results  for the  extreme (NDF  2) conditions  (see  figure  3  at the  additional pages  for  aver- aged  results),  in  which  the object  without  the  filter  was extremely dominant.   In  these  cases  the  primarily matte bird  was judged  to  be rather average  on all scales,  the primarily  glossy bird  was judged  to  be extremely glossy,  very hard,  very cold and a little heavier, and the primarily velvety bird  was rated to be quite matte, soft, warm  and  of average weight.   We  found  the ratings to vary  systematically as  a function of the weights, see figure 4. The average  ratings for the four properties correlated (R2  range  0.74–0.92).   3.   DISCUSSION We constructed a novel type of setup  with  which  we can optically  mix  real  stimuli.  Clear  advantages  of this  setup are  that we  can  use  real  objects   (so  that  dynamic range and  resolution are not an issue) and  still vary  their material properties in a very systematic way.  Furthermore, the setup allows for a wide range  of other  possible  manipulations, e.g. mixing  objects  and  scenes  / contexts  and  mixing  different lighting settings.  We are  currently exploring  various  applications.  Superpositions of objects  do  not correspond to interpolated  optical  properties,  such   as  linear   combinations  of BRDF’s   (e.g.    matte plus  shiny  is  assumed to represent glossy).    This  is due  to interreflections [4] (at the  micro-, meso-  and  macroscales!).  Thus,   the optically mixed  stimuli cannot simply  be considered as physical  mixes.  Instead, they should  be considered as ”painterly mixes” of the most salient features of the two components, for instance white highlights on the glossy green bird,  smooth shading  over the matte green bird and white contours on the velvety  bird (the main  characteristic of asperity scattering [3]). We  found  robust and  systematical results  that vary  ac- cording  to  the weights of our  optical mixtures.  Thus,  our novel  setup   works  as  it  is  supposed to.    Observers  commented that they thought we actually presented birds  made of varying  materials and  varying  lighting. Another interesting finding  is that our  optical  mixtures covary  consistently in perceived  glossiness, softness,  warmth and heaviness, even though the  latter three  are  properties that are  not directly related to the optical properties.   4.   ACKNOWLEDGMENTS Maarten Wijntjes was supported by the Netherlands Organisation for Scientific Research (NWO).   5.   REFERENCES [1] K. Dana  and  B. van  Ginneken. Reflectance and  texture of real-world surfaces.  Proceedings IEEE  Computer Science  Conference on Computer Vision  and  pattern Recognition, 1977. [2] E. Karana, P.  Hekkert, and  P.  Kandachar. Meanings  of materials through sensorial  properties and manufacturing processes.  Materials and  Design, 30:2778–2784, 2009. [3] J. Koenderink and  S. Pont. Material properties for surface  rendering. International Journal for Computational Vision  and  Biomechanics, 1(1):43–53, 2008. [4] S. Pont and  J. Koenderink. Reflectance from locally glossy thoroughly pitted surfaces.  Computer Vision  and Image  Understanding, 98:211–222, 2005.         Predicting Perceptions: Proceedings of the 3rd International Conference on Appearance, pp. 9-12, Edinburgh, UK, ISBN 978-1-4716-6869-2, April 2012.             Figure 3:  A  bargraph of  the average ratings for the NDF 2 cases. The different colors depict  the ratings for the different  properties,  on a normalized range (of 0  to 1), with red for matte-glossy, green for hard-soft, blue for cold-warm and black for light-heavy  ratings.  The three main clusters represent  the conditions in which, from left  to right, the matte, glossy and velvety  birds were dominant  (no NDF or weight  1.0).  For each rating we  show two  bars, representing  the two  possible object  combinations (the second materials or the severely attenuated objects with weight  0.01 are noted between  brackets below the graph). Note that in some cases the two  bars differ, indicating an influence of  the 100  times attenuated object.                       Predicting Perceptions: Proceedings of the 3rd International Conference on Appearance, pp. 9-12, Edinburgh, UK, ISBN 978-1-4716-6869-2, April 2012.              Figure 4:  The average ratings (on a normalized range of 0–1) as  a function of the difference between the NDF values, for the velvety  –  matte (left  column), the velvety  –  glossy (centre column), and the matte –glossy (right column) birds combinations. The rows depict, from top to bottom, the ratings on the matte – glossy, hard – soft, cold – warm and light  – heavy properties. 

Perceptual Qualities of Optically Mixed Materials

https://zenodo.org/record/811604/files/Perceptual_Qualities_of_Optically_Mixed_Materials.pdf

Perceptual Qualities of Optically Mixed Materials

Abstract

Similar works

Full text

Available Versions

ZENODO