{"id":40200,"date":"2019-12-03T07:20:10","date_gmt":"2019-12-03T07:20:10","guid":{"rendered":"http:\/\/www.labri.fr\/perso\/barla\/blog\/?p=40200"},"modified":"2019-12-03T07:24:39","modified_gmt":"2019-12-03T07:24:39","slug":"transparencies","status":"publish","type":"post","link":"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=40200","title":{"rendered":"Transparencies"},"content":{"rendered":"<p id=\"top\" \/>\n<h3 class=\"wp-block-heading\">Creepy transparency<\/h3>\n\n\n\n<p>The notion of transparency might seem clear at first sight: one object  is seen behind another. <br>On the physical side, transparency may occur in two different ways:  transmission and coverage. Colors may thus be\u00a0tinted and darkened by the material and thickness of the front object. But you may also have a structure with many tiny holes (like a screen) letting a background object show up! <br>Transparency also occurs in motion: the motion of a transmitting surface  on top of a moving or still background. But also the motion of trees layed out in depth, with interstices  between branches letting other trees show up. <br>When considering the perception of transparency, the concept is  less clear than you may think. Consider these statues giving the illusion of a veil on a woman face  (<a href=\"http:\/\/abcgreatpix.com\/sculpture%2Bwoman%2Bveil\">http:\/\/abcgreatpix.com\/sculpture%2Bwoman%2Bveil<\/a>). Even if we know there&#8217;s only a single surface here, shape appears to be composed of multiple layers. And for multiple layers to be laid on top of each other, there&#8217;s no  other explanation but transparency! <br>You not only need multiple layers, but also an ordering: one must be in  front of the other, and THIS is\u00a0what leads to perceived transparency! The same thing may happen again in motion: simply move your fist behind  your t-shirt, and you&#8217;ll see what I mean&#8230; <br>For some reason, it has a creepiness potential that makes it used over  and over in horror movies such as Alien or Ghost vs Ghost&#8230; <\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Forgiving transparency<\/h3>\n\n\n\n<p>Many different causal factors to distortions in transparent objects  (distance to background, thickness, refractive index). Impossible to discount these causes, which might be why our visual  system is so forgiving about exactness of distortions (Yeung&#8217;s paper). <br>Drawing books (e.g., Hogarth&#8217;s) and tutorials recommend a mere  &#8220;recording&#8221; of these distortions ; but there&#8217;s obviously many degrees of  freedom there. When is a distorted pattern actually perceived as due to transparency?  How much inaccurate can it be? What&#8217;s the role of superimposed reflections? <br>For thick objects, distortions are always present due to back facing  surfaces, even with perspective or even homogeneous background (what  about TIR?). Challenge is to find sufficient conditions for the perception of  transparency (in static\/dynamic scenario), then maybe refine them to get  a proper depiction. <\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Different flavors of translucency<\/h3>\n\n\n\n<p>Homogeneous translucent materials such as wax appear quite different  from multi-layered translucent ones such as skin. One important visual difference seems to be in the relationship between the translucent and specular components of lighting. In the homogeneous case, highlights seem to float over the material, as if the two types of shading components were unrelated. In the multi-layered case, the transucent component follows much better  the patterns of highlights. Why is that so?  <br>Other flavors of translucency actually exist. For instance, hollow  objects (like a balloon) look different than filled in objects (like marble). With a same material, appearance may also vary dramatically depending on  lighting, especially when it comes from behind, or worse, from inside! In the latter case, the patterns of shading are completely reversed. A  similar example occurs when looking at light from under a blanket&#8230; <br>[Mention work by Bei Xiao, Philipp Marlow &amp; Bart Anderson, others from  PRISM]. <br>What are the different visual cues that distinguish these modes of  appearance? <\/p>\n","protected":false},"excerpt":{"rendered":"<p>Creepy transparency The notion of transparency might seem clear at first sight: one object is seen behind another. On the physical side, transparency may occur in two different ways: transmission and coverage. Colors may thus be\u00a0tinted and darkened by the material and thickness of the front object. But you may also have a structure with &#8230; <a title=\"Transparencies\" class=\"read-more\" href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=40200\" aria-label=\"Read more about Transparencies\">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-40200","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\/40200","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=40200"}],"version-history":[{"count":3,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/40200\/revisions"}],"predecessor-version":[{"id":40203,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/40200\/revisions\/40203"}],"wp:attachment":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=40200"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=40200"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=40200"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}