{"id":40004,"date":"2019-05-20T07:29:58","date_gmt":"2019-05-20T07:29:58","guid":{"rendered":"http:\/\/www.labri.fr\/perso\/barla\/blog\/?p=40004"},"modified":"2019-06-24T12:49:30","modified_gmt":"2019-06-24T12:49:30","slug":"glossy-grapes-w-f-di-cicco","status":"publish","type":"post","link":"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=40004","title":{"rendered":"Glossy grapes w\/ F. di Cicco"},"content":{"rendered":"<p id=\"top\" \/>\n<p>I was first expecting that you would compare the cropped out grapes as      shown in Figure 3, with larger views showing objects around. You chose instead to look at two &#8220;windows&#8221; in the image, which is interesting too, but is more about scale than context. Coming back to a single grape, I find it surprising that when cropped out, it does not look so glossy to me&#8230; It has actually been mentioned in the book &#8220;On Reflection&#8221;, by Jonathan Miller (great book!); but never studied as far as I know.<\/p>\n\n\n\n<p style=\"text-align:right\"><em>We didn&#8217;t test the cropped grapes but we did a rating experiment showing the bunches as in figure 1 left, with one grape per time annotated and we asked to rate just glossiness of that specific grape. The results weren&#8217;t significantly different from rating the entire bunch. But you are right, the glossiness look very different when taken completely out of context and it would be interesting to investigate it further. <\/em><\/p>\n\n\n\n<p>I also wonder whether we discard cracks because we know it&#8217;s a painting,      or whether we would do the same with more abstract (still irrelevant)      texture patterns&#8230;<\/p>\n\n\n\n<p style=\"text-align:right\"><em>In my opinion we disregard the cracks more easily than other texture effects, like seeing the texture of the canvas or the brushstrokes (see image 8 and 13 in the supplementary material for example).<\/em><\/p>\n\n\n\n<p>The thin dark halos around highlights might be specific to the depiction      of translucency; books on scientific illustration recommend these      patterns (as in Phyllis Wood&#8217;s book if I remember well).<\/p>\n\n\n\n<p style=\"text-align:right\"><em>There is indeed a darker shading of the grapes color around the highlights in most of the grapes, as illustrated in the book you mentioned, and we also found high correlation between glossiness and translucency perception, but I think that these very dark lines just along the highlights are something different. I don&#8217;t know if they were applied on purpose but they really enhance the contrast of the highlights and overall the bunch look extremely glossy, more like glass than grapes.<\/em><\/p>\n\n\n\n<p>I have found your observation on the non-congruent shape of highlights      very interesting. I&#8217;d say that with such quasi-isotropic shapes, any anisotropic light source (e.g., a tall window) might produce such reflections.     Still, the reflections are different from grape to grape; but we don&#8217;t really notice that, and the painters (perhaps knowingly) exploit this&#8230; Other highlights are more distorted, which suggests dimples in grape shapes; in this case, only the highlights seem to convey shape.<\/p>\n\n\n\n<p style=\"text-align:right\"><em>I am not completely sure if I understood your last comment because we didn&#8217;t look into the perception of the shape of the grapes from the shape of the highlights. We analysed the congruency of the orientation of the highlights and we found that congruency is not related to glossiness perception of grapes. We probably don&#8217;t notice the incongruent orientations because each grape has its own orientation and all together they show different orientations in the bunch, so we maybe don&#8217;t really pay attention to the directions of orientation as long as they are different.<\/em><\/p>\n\n\n\n<p>Regarding my last comment, I was mostly interested in the incongruent orientations of highlights that we do not seem to notice, independently of glossiness perception. I&#8217;m wondering two different things: to which extent incongruency can be explained physically (e.g., by the presence of an elongated window in the &#8220;wrong&#8221; orientation), and in which case are we sensitive or ignorant to such incongruencies in practice.<br>\nSaid differently, if I were to paint grapes, since I&#8217;m so bad in general at painting and drawing, I might create so much incongruency that it might look &#8220;unrealistic&#8221;; even though both the painting by a master and my painting (if you could call it that way) are physically unrealistic. What makes the painting by the master so much more compelling, yet still physically inaccurate? What are the tricks?<\/p>\n\n\n\n<p style=\"text-align:right\"><em>I don&#8217;t have an answer yet to these questions but I am also very interested in how far painters can go with physical errors, like incongruent highlights, before we become aware of them and when they actually impair our perception of realism. I am also wondering if the amount of incongruence may be connected to the degree of anisotropy of the different materials depicted. I saw that you have worked a lot with the highlights of anisotropic materials and I would be glad to discuss this further with you. <\/em><\/p>\n\n\n\n<p>One precision regarding anisotropy: this is a term that&#8217;s used for many different things, and it can be confusing. Anisotropic <strong>materials<\/strong>, like the ones I&#8217;ve worked on in the past,  are a bit specific: they are made of elongated structures at a  micro-scale. They are not very common, but interesting to study as they  produce surprising highlights. In a previous email, we were also talking about anisotropic <strong>surface features<\/strong>,  such as ridges, valleys or folds on a surface. At a local surface  point, this amounts to having different principal curvatures (hence it&#8217;s  very common). <strong>Lighting<\/strong> might be anisotropic as well, such as with a neon light  source, a tall window letting light through, or trees blocking skylight  in a forest.<br> Finally, <strong>highlights<\/strong> themselves may be called anisotropic. This  may be either because they are distorted by an anisotropic shape, or  because the material itself is anisotropic, or because the lighting is  anisotropic&#8230; or any of these reasons combined! <br><br>My intuition is that we are not much aware of the lighting environment:  two different reflections on nearby grapes of similar shape and  (isotropic) material usually do not yield any surprise, as if they could  be lit by two different environments; even though this is impossible,  we do not seem to care. But why don&#8217;t we see the two grapes as made of  different (anisotropic) materials instead? Ok it&#8217;s rather unlikely. But  then why don&#8217;t we perceive the grapes as having different shapes that  could explain the different highlights? This might actually happen with  some weirdly-shaped grape, right? Hence there must be something in the  aspect of the highlights that suggests that it reasonably fits the  underlying shape: some sort of congruence. Artists are able to produce  such &#8220;illusions&#8221;, how to they manage that trick? <br><\/p>\n","protected":false},"excerpt":{"rendered":"<p>I was first expecting that you would compare the cropped out grapes as shown in Figure 3, with larger views showing objects around. You chose instead to look at two &#8220;windows&#8221; in the image, which is interesting too, but is more about scale than context. Coming back to a single grape, I find it surprising &#8230; <a title=\"Glossy grapes w\/ F. di Cicco\" class=\"read-more\" href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=40004\" aria-label=\"Read more about Glossy grapes w\/ F. di Cicco\">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":[21],"tags":[],"class_list":["post-40004","post","type-post","status-publish","format-standard","hentry","category-discuss"],"_links":{"self":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/40004","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=40004"}],"version-history":[{"count":3,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/40004\/revisions"}],"predecessor-version":[{"id":40009,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/40004\/revisions\/40009"}],"wp:attachment":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=40004"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=40004"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=40004"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}