{"id":40195,"date":"2019-12-03T07:11:27","date_gmt":"2019-12-03T07:11:27","guid":{"rendered":"http:\/\/www.labri.fr\/perso\/barla\/blog\/?p=40195"},"modified":"2019-12-03T07:17:15","modified_gmt":"2019-12-03T07:17:15","slug":"material-qualities","status":"publish","type":"post","link":"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=40195","title":{"rendered":"Material qualities"},"content":{"rendered":"<p id=\"top\" \/>\n<h3 class=\"wp-block-heading\">Types of gloss<\/h3>\n\n\n\n<p>Remind Hunter and qualities of gloss for opaque materials. Materials also exhibit color-changing effects (iridescence), grazing-angle effects, diffuse effects (necessary for contrast), retro-reflection? <br>Haze and distinctness of images are properties of gloss itself.  Iridescence as well, but depends on viewing angle. Sheen seems to be a special type of gloss mostly related to Fresnel  effects: it may exist on its own, or modulate gloss. <br>Last property is texture, and it&#8217;s a world in itself! It&#8217;s actually a  matter of scale, although it could be responsible for high-frequency  effects (glitter, scratches, etc). <br>This is only for opaque materials, meaning light traveling a short distance inside the material from the point of view. Actually even diffuse looks translucent for extremely close views. But  this is another story for another post&#8230; <\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Material forensics<\/h3>\n\n\n\n<p>How to distinguish materials that are made to imitate (usually more  expensive) materials from the originals? Which cues are involved? How can we improve the imitation, at least in still images? <br>For instance, metals look brighter and less saturated than coated metallic and plastic counterparts. Because of inter-reflections in cavities, they also show up more contrast in value and saturation. This does not happen with plastic since only the specular layer gets  &#8220;darker&#8221;, leaving mostly diffuse reflection. <br> The shape and nature of reflections also differs between (coated) metallic and plastic\/lacquered materials. It seems that only the brightest sources are apparent in the latter case. <\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Material-induced DoF<\/h3>\n\n\n\n<p>The &#8220;Nude in the shower&#8221; effect is an example of how material cues are  conveyed when objects vary with distance (up to contact), c.f. Bohren. <br>The very same transmission-based effect occurs on reflection, especially  on more or less rough metals (seems much less significant for di-electrics). Due to spatial\/angular correlations of the lighting environments for  neighboring surface locations, the material acts as an optical system  with depth of field. <br>When close to actual contact, the cast shadow tends to merge with the  transmitted or reflected image of the surroundings. <\/p>\n\n\n\n<h3 class=\"wp-block-heading\">The shady side of gloss<\/h3>\n\n\n\n<p>On a sunny day, a shiny object seen on its shady side will cast a shadow on the ground or other nearby objects. The shadow will itself be reflected off the part of the shiny object that is in the shade. <br>The contrast of the reflection depends on the diffuseness of the lighting and the albedos of the shadow receivers. But in any case, this adds useful variations in the reflected environment that help convey properties of the material. <br>Is this actually used in lighting design techniques? How is it related  to the dark side of gloss?<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">White out!<\/h3>\n\n\n\n<p>Increasing multiple scattering or the number of single scattering events  that reach the eye both have the effect of whitening and blurring out  images of objects. This occurs in participating media such as when seeing an object through  fog or a turbid liquid, yielding reduced contrast and smoothing. <br>But it also occurs when objects are seen through transparent and rough slabs, as in the example of the shower door. It may even occur at the surface of a single object, near the silhouette  of fluffy surfaces where more scattering occurs. <\/p>\n","protected":false},"excerpt":{"rendered":"<p>Types of gloss Remind Hunter and qualities of gloss for opaque materials. Materials also exhibit color-changing effects (iridescence), grazing-angle effects, diffuse effects (necessary for contrast), retro-reflection? Haze and distinctness of images are properties of gloss itself. Iridescence as well, but depends on viewing angle. Sheen seems to be a special type of gloss mostly related &#8230; <a title=\"Material qualities\" class=\"read-more\" href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=40195\" aria-label=\"Read more about Material qualities\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[772],"tags":[],"class_list":["post-40195","post","type-post","status-publish","format-standard","hentry","category-blog"],"_links":{"self":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/40195","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=40195"}],"version-history":[{"count":4,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/40195\/revisions"}],"predecessor-version":[{"id":40199,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/40195\/revisions\/40199"}],"wp:attachment":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=40195"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=40195"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=40195"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}