{"id":35951,"date":"2014-12-02T15:28:14","date_gmt":"2014-12-02T15:28:14","guid":{"rendered":"http:\/\/www.labri.fr\/perso\/barla\/blog\/?p=35951"},"modified":"2019-08-13T11:20:13","modified_gmt":"2019-08-13T11:20:13","slug":"scratches-and-glints","status":"publish","type":"post","link":"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=35951","title":{"rendered":"Scratches and fibers"},"content":{"rendered":"<p id=\"top\" \/>\n<h3 class=\"wp-block-heading\">Real-world materials<\/h3>\n\n\n\n<p>Natural: Hair\/fur, petal, leaves, algae, skins (onions), fingerprints, feathers, cut wood, waves, striated gems.<\/p>\n\n\n\n<p>Artificial: scratched metal\/plastic\/glass\/ceramics, machined surfaces, synthetic\/natural cloth, compressed surfaces.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Glint lines<\/h3>\n\n\n\n<p>A set of perfectly parallel scratches is already able to produce glint lines, provided either surface curvature or near-field lighting are present. Individual glints will be more contrasted using sharp, strong and thin light sources, which alternate between highs and lows of BRDF lobes. Local microscopic inter-reflections will produce more glints of varying intensity, but with less contrast since lobes are not clearly separate.<\/p>\n\n\n\n<p>For strictly parallel scratches, contributing light sources lie in a specific BRDF cone ; adding orientation variations will produce super-imposed cones. As a result, more lights will be able to contribute, resulting in more glint lines whose distribution will vary with orientation distribution and curvature. Further adding variations in the scratch distribution (spacing, size, occurrence) will create a visible patterning of glint lines on the surface.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Highlight contours<\/h3>\n\n\n\n<p>A strong area light source will produce an extended highlight on the surface whose shape depends on curvature and scratch trajectories. The silhouette of the highlight will exhibit a high-frequency pattern due to the edge of the source producing a network of glint lines. The sharpest the source edge, the more contrasted the corresponding highlight silhouette pattern will be (what about edge orientation?).<\/p>\n\n\n\n<p>Of course, the regularity of the pattern will directly depend on the regularity of the scratch distribution. In some particular configurations, &#8220;negative&#8221; glint lines will appear from inside the highlight, due to local shadowing and masking. As before, this should be less pronounced when taking into account inter-reflections, that increase chances to hit the key area light.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Directional smear<\/h3>\n\n\n\n<p>Low-key reflections will tend to be blurred together by a complex directional filter kernel that depends on BRDF content. The single scattering component will have the effect of smearing reflected images in a direction orthogonal to the main scratch direction. <\/p>\n\n\n\n<p>If scratches are sufficiently spaced apart but still densely distributed, then a sharp reflection will occur in conjunction with the smeared one. This will be mostly visible on highlights of course, but other reflections will still appear in a kind of hazy smeared reflection. Similar hazy reflections might occur due to multiple scattering that add a directional, yet low-frequency cone-lobe to the BRDF.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Fiber distributions<\/h3>\n\n\n\n<p>When fibers are parallel to mean curvature, the highlight is washed out and spread quite uniformly. When fibers are perpendicular to the min curvature direction, variations occur in both ridges and valleys, which tends to create &#8220;highlight loops&#8221;!<\/p>\n\n\n\n<p>When fibers &#8220;stick out&#8221; of the surface, then only a sub-segment of each fiber contributes to highlights, hence the complex &#8220;velvety&#8221; appearance. One may thus manipulate tangents of fibers so that they focus, spread or even displace\u00a0 highlights on a surface!<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Real-world materials Natural: Hair\/fur, petal, leaves, algae, skins (onions), fingerprints, feathers, cut wood, waves, striated gems. Artificial: scratched metal\/plastic\/glass\/ceramics, machined surfaces, synthetic\/natural cloth, compressed surfaces. Glint lines A set of perfectly parallel scratches is already able to produce glint lines, provided either surface curvature or near-field lighting are present. Individual glints will be more contrasted &#8230; <a title=\"Scratches and fibers\" class=\"read-more\" href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=35951\" aria-label=\"Read more about Scratches and fibers\">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":[651],"tags":[],"class_list":["post-35951","post","type-post","status-publish","format-standard","hentry","category-thoughts"],"_links":{"self":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/35951","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=35951"}],"version-history":[{"count":11,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/35951\/revisions"}],"predecessor-version":[{"id":40074,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/35951\/revisions\/40074"}],"wp:attachment":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=35951"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=35951"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=35951"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}