{"id":66,"date":"2019-08-19T16:35:21","date_gmt":"2019-08-19T08:35:21","guid":{"rendered":"https:\/\/cgda.csie.ncnu.edu.tw\/wordpress\/?page_id=66"},"modified":"2019-08-19T16:37:08","modified_gmt":"2019-08-19T08:37:08","slug":"group-phonton-mapping","status":"publish","type":"page","link":"https:\/\/cgda.csie.ncnu.edu.tw\/wordpress\/?page_id=66","title":{"rendered":"Grouped Photon Mapping"},"content":{"rendered":"\n<p>For the purpose of cutting simulation and visualization of \ndiamonds, it is necessary to synthesize accurate images of diamonds. \nTherefore, several optical phenomena of diamonds such as the dispersion,\n total reflection, and caustics effects should be correctly represented.\n Besides, the very complicated illuminating and shadowing phenomena \ninside of diamonds have a great effect on a diamond\u2019s appearance. These \nphenomena are due to the optics properties, and the cutting shapes\u2019 \ngeometry of diamonds. Because rays of light do reflect off many times \nwithin a diamond, it is very difficult to predict how many indirect \nshadow rays will go to the eyes. Thus, the problem mentioned above can \nnot be handled correctly by adopting a standard single pass ray tracing \nmethod.<\/p>\n\n\n\n<figure class=\"wp-block-image\"><img decoding=\"async\" src=\"http:\/\/163.22.17.152\/cglab\/images\/cur_1_1.jpg\" alt=\"\"\/><\/figure>\n\n\n\n<figure class=\"wp-block-image\"><img decoding=\"async\" src=\"http:\/\/163.22.17.152\/cglab\/images\/cur_1_2.jpg\" alt=\"\"\/><\/figure>\n\n\n\n<p>Photon mapping is an efficient global illumination method. It can \nbe generally applied to simulate various visual or optical effects in \ncomplex scenes, especially caustics. However, photon mapping adopts the \nnearest-neighbor density estimation method, the result tends to generate\n systematic errors including proximity, boundary, and topological bias \nrespectively. In addition, for some special objects such as diamonds, \nthe transmission paths of light rays inside the object are so \ncomplicated that it would result in intolerable visual defects using \nstandard photon mapping method.\nIn this dissertation, we propose a novel architecture, grouped photon \nmapping, by combing standard photon mapping with the light-beam concept \nto improve the nearest-neighbor density estimation method. Based on the \nray coherence of a light-beam, we cluster all photons into different \nbeam-like groups of photons, where the photons in the same group have a \ncoherent intersection-history in their transmission paths. We store each\n photon group in an isolated photon map which is also used to maintain a\n polygonal boundary to rebuild a beam-like illuminated area by the \ndistribution of the photons. The illumination area forms a natural and \naccurate sampling area to filter the neighbor photons around the query \npoint in the nearest-neighbor query stage. In addition, we apply a Level\n of Detail technique and an intuitive strategy for managing the process \nof reorganizing groups to achieve a trade-off between bias and noise. \nFinally, in terms of efficiency, we construct a double-layer kd-tree \nconsisting of group and photon nodes respectively. This data structure \nis useful to first exclude most of unrelated photon groups and reduce \nthe time on the point-boundary intersection testing and searching for \nthe nearest-neighbor photons.\nThe experiment results prove that our method can successfully reduce \nnoise and bias,\nV\nand eliminate light leakage. Especially, for a gemstone object with \ncomplicated caustic effects, we can smoothly synthesize a high-quality \nimage.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>For the purpose of cutting simulation and visualization &hellip; <a href=\"https:\/\/cgda.csie.ncnu.edu.tw\/wordpress\/?page_id=66\" class=\"more-link\">\u95b1\u8b80\u5168\u6587 <span class=\"screen-reader-text\">Grouped Photon Mapping<\/span> <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":3,"featured_media":0,"parent":30,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"_links":{"self":[{"href":"https:\/\/cgda.csie.ncnu.edu.tw\/wordpress\/index.php?rest_route=\/wp\/v2\/pages\/66"}],"collection":[{"href":"https:\/\/cgda.csie.ncnu.edu.tw\/wordpress\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/cgda.csie.ncnu.edu.tw\/wordpress\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/cgda.csie.ncnu.edu.tw\/wordpress\/index.php?rest_route=\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/cgda.csie.ncnu.edu.tw\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=66"}],"version-history":[{"count":3,"href":"https:\/\/cgda.csie.ncnu.edu.tw\/wordpress\/index.php?rest_route=\/wp\/v2\/pages\/66\/revisions"}],"predecessor-version":[{"id":69,"href":"https:\/\/cgda.csie.ncnu.edu.tw\/wordpress\/index.php?rest_route=\/wp\/v2\/pages\/66\/revisions\/69"}],"up":[{"embeddable":true,"href":"https:\/\/cgda.csie.ncnu.edu.tw\/wordpress\/index.php?rest_route=\/wp\/v2\/pages\/30"}],"wp:attachment":[{"href":"https:\/\/cgda.csie.ncnu.edu.tw\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=66"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}