{"id":39776,"date":"2018-07-31T08:17:45","date_gmt":"2018-07-31T08:17:45","guid":{"rendered":"http:\/\/www.labri.fr\/perso\/barla\/blog\/?p=39776"},"modified":"2019-08-14T15:52:47","modified_gmt":"2019-08-14T15:52:47","slug":"wetness-w-ted-masa-shinya","status":"publish","type":"post","link":"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=39776","title":{"rendered":"Wetness w\/ Ted, Masa &#038; Shin&#8217;ya"},"content":{"rendered":"<p id=\"top\" \/><p>[Ted]<br \/>I&#8217;m forwarding an email that I sent to Shin&#8217;ya and Masa showing some pebbles. The fact that color and contrast are enhanced is familiar to anyone who has collected pebbles on the beach. An additional effect is evident on the first pebble. The medium scale relief shows much less shading in the wet region.<\/p>\n<p><a href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2018\/07\/peeble2.jpg\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2018\/07\/peeble2-300x225.jpg\" alt=\"\" width=\"300\" height=\"225\" \/><\/a> <a href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2018\/07\/peeble3.jpg\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2018\/07\/peeble3-300x225.jpg\" alt=\"\" width=\"300\" height=\"225\" \/><\/a><\/p>\n<p>My guess is that this is due to the reduced vignetting of illumination, as illustrated in this sketch. Light which comes from a grazing angle in air (a) is redirected to a more vertical angle after refraction with the air-water interface (b). So the shading is weaker.<\/p>\n<p><a href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2018\/07\/vignetting.png\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2018\/07\/vignetting-1024x291.png\" alt=\"\" width=\"500\" height=\"142\" \/><\/a><\/p>\n<p>It is also interesting to compare the case of a pebble submerged in water with the case of a wet pebble. With the wet pebble, the water hugs the contour of pebble, and the air-water interface stays close to the mineral surface. With the submerged pebble, that interface is far from the mineral surface.<\/p>\n<p>The submerged pebble case is trickier that it might seem. Are the light sources also submerged? Or are they in the air, above the water? And is the viewer&#8217;s eye submerged or above the water? These different conditions lead to different results. In particular, if the light sources are in the air, and the air-water interface is planar, then the range of illumination angles striking the pebble is limited.<\/p>\n<p>[Masa]<br \/>This is just a reminder, and a notification to Pascal, about the demo movies I made two and a half years ago.<br \/>From the pebble demo (Pebble.mp4), you will see quite different impression between the pebble submerged in water and the wet pebble.<br \/>Please download the files from the following link.\u00a0<a href=\"https:\/\/www.dropbox.com\/s\/3azbqcg78kc3lv8\/WetDemo20151222.zip?dl=0\">https:\/\/www.dropbox.com\/s\/3azbqcg78kc3lv8\/WetDemo20151222.zip?dl=0<\/a><\/p>\n<div>\u00a0<\/div>\n<div>[Pascal]<br \/>Interesting how the two cases (wet and submerged) can be so different when one pays attention!<\/div>\n<div>\n<p>The submerged pebble not only changes in terms of material at a micro-scale (due to water penetrating the porous material, and having an index higher than air), but it also changes the surrounding light-field as mentioned by Ted. It&#8217;s actually something one can easily observe by looking toward the water surface from below: the horizon is literally compressed due to refraction.<\/p>\n<p>For the wet pebble, the change in micro-scale material is the same as the submerged one, but on top of that the air-water interface brings an additional layer of reflections that will follow the pebble surface, but not perfectly since it might have its own relative fluctuations due to surface tension for instance. This is another meso-scale aspect of the appearance of wet surfaces that I think we&#8217;re quite sensitive to!<\/p>\n<p>One obvious example is that of a puddle, as in the attached image. Surface tension near the gravel locally distorts reflections and in several places brings out highlights that follow its contours. This does not only occur at the puddle boundaries, but also everywhere on the wet surface. Hence the relationship between the ground\/pebble surface and the water interface may also provide strong cues to wetness.<\/p>\n<p><a href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2018\/07\/puddle.jpg\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2018\/07\/puddle.jpg\" alt=\"\" width=\"960\" height=\"700\" \/><\/a><\/p>\n<\/div>\n<p>[Shin&#8217;ya]<br \/>I wonder how easy\/difficult to test the impact of these factors on human wetness perception using CG.<\/p>\n<p>[Pascal]<br \/>I think that it might be interesting to work with compositing techniques to create &#8220;wetness stimuli&#8221;. Most renderers permit to output different buffers: diffuse, reflections, but also shadows, depth and normals. These are often used at the compositing\/post-processing stage to adjust or add lighting or camera effects. I don&#8217;t think this has been used much (or at all) in psychophysics; but it could be interesting here.<\/p>\n<p>The idea would be to render a dry object on a uniform background (like a pebble of course). Then each of the visual factors we discussed in previous emails could be affected by compositing operations.<\/p>\n<p>First, a layer of water could be added on top, in ways that are more or less correlated to the object shape. This could be done by starting from the rendered normal buffer, distorting it to some extent, and using it to create reflections. We have already tried such &#8220;decorrelation&#8221; of image layers with a colleague to depict translucency. See this video where we took inspiration from a paper by Motoyoshi (around 3:30): <a href=\"https:\/\/vimeo.com\/41569166\">https:\/\/vimeo.com\/41569166<\/a><br \/>I think something similar but more subtle is at work in the perception of wetness, due to surface tension effects in particular. In contrast, with a pebble submerged in water, the water layer (flat or not) will not be correlated at all with the pebble surface shape.<\/p>\n<p>Second, the appearance of the original dry pebble should itself be affected, starting with colors of the diffuse buffer using your WET operator. But we could go farther by reducing the intensity of the reflection buffer coming from rendering to mimic index matching as I suggested. For meso-scale roughness, we could modify the shadow buffer (not sure how, maybe warping?) to affect vignetting as mentioned by Ted.<\/p>\n<p>All of these effects could be applied in a spatially-varying manner, as in Ted&#8217;s photos of half-dry \/ half-wet pebbles.<\/p>\n<p>I don&#8217;t know whether this would easily lend itself to a set of psychophysical experiments with a reasonable number of stimuli. What would be the main question(s) about? The amount of wetness or the difference between wetness and submersion?<\/p>\n\n\n<p><\/p>\n","protected":false},"excerpt":{"rendered":"<p>[Ted]I&#8217;m forwarding an email that I sent to Shin&#8217;ya and Masa showing some pebbles. The fact that color and contrast are enhanced is familiar to anyone who has collected pebbles on the beach. An additional effect is evident on the first pebble. The medium scale relief shows much less shading in the wet region. My &#8230; <a title=\"Wetness w\/ Ted, Masa &#038; Shin&#8217;ya\" class=\"read-more\" href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=39776\" aria-label=\"Read more about Wetness w\/ Ted, Masa &#038; Shin&#8217;ya\">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-39776","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\/39776","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=39776"}],"version-history":[{"count":9,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/39776\/revisions"}],"predecessor-version":[{"id":40136,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/39776\/revisions\/40136"}],"wp:attachment":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=39776"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=39776"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=39776"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}