{"id":8,"date":"2024-04-03T23:31:26","date_gmt":"2024-04-03T20:31:26","guid":{"rendered":"https:\/\/sisu.ut.ee\/imageprocessing\/4-2\/"},"modified":"2024-04-03T23:31:31","modified_gmt":"2024-04-03T20:31:31","slug":"4-2","status":"publish","type":"page","link":"https:\/\/sisu.ut.ee\/imageprocessing\/4-2\/","title":{"rendered":"4. Aliasing and image enhancement"},"content":{"rendered":"<p><span style=\"color: #000000\">Digital sampling of any signal, whether sound, digital photographs, or other, can result in apparent signals at frequencies well below anything present in the original. Aliasing occurs when a signal is sampled at a less than twice the highest frequency present in the signal.\u00a0Signals at frequencies above half the sampling rate\u00a0must\u00a0be filtered out to avoid the creation of signals at frequencies not present in the original sound. Thus digital sound recording equipment contains low-pass filters that remove any signals above half the sampling frequency.<\/span><\/p><p><span style=\"color: #000000\">Since a sampler is a linear system, then if an input is a sum of sinusoids, the output will be a sum of sampled sinusoids. This suggests that if the input contains no frequencies above the Nyquist frequency, then it will be possible to reconstruct each of the sinusoidal components from the samples. This is an intuitive statement of the\u00a0Nyquist-Shannon\u00a0sampling theorem.<\/span><\/p><p><span style=\"color: #000000\">Anti-aliasing is a process which attempts to minimize the appearance of aliased diagonal edges. Anti-aliasing gives the appearance of smoother edges and higher resolution. It works by taking into account how much an ideal edge overlaps adjacent pixels.<\/span><\/p><p><span style=\"color: #000000\">In this lecture we will talk about spatial aliasing and anti-aliasing. Also we will start to talk about image enhancement. Two main categories of image enhancement will be introduced. Point process and neighbour process will be defined. Finally we will give an introduction on definition of contrast.<\/span><\/p><p style=\"text-align: center\"><span style=\"color: #000000\"><div class=\"ratio ratio-16x9 mb-3\"><div class=\"video-placeholder-wrapper video-placeholder-wrapper--16x9\">\n\t\t\t    <div class=\"video-placeholder d-flex justify-content-center align-items-center\">\n\t\t\t        <div class=\"overlay text-white p-2 w-100 text-center d-block justify-content-center align-items-center\">\n\t\t\t            <div>To view third-party content, please accept cookies.<\/div>\n\t\t\t            <button class=\"btn btn-secondary btn-sm mt-1 consent-change\">Change consent<\/button>\n\t\t\t        <\/div>\n\t\t\t    <\/div>\n\t\t\t<\/div>\n<\/div><\/span><\/p><p style=\"text-align: center\"><\/p><p style=\"text-align: center\"><a href=\"http:\/\/www.uttv.ee\/naita?id=20094\" target=\"_blank\" rel=\"noopener\">http:\/\/www.uttv.ee\/naita?id=20094<\/a>\u00a0<\/p><p style=\"text-align: center\"><a href=\"http:\/\/youtu.be\/SwRYL_fk_DA?list=UU-ETlxdihAaw8Pn6_Zz10lg\" target=\"_blank\" rel=\"noopener\">http:\/\/youtu.be\/SwRYL_fk_DA?list=UU-ETlxdihAaw8Pn6_Zz10lg<\/a><\/p><p style=\"text-align: justify\"><span style=\"color: #000000\">Review the attached document.<\/span><\/p><br><div class=\"wp-block-group attached-files-group is-layout-constrained wp-block-group-is-layout-constrained\"><div class=\"wp-block-file\"><a href=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/105\/aliasing.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">aliasing.pdf<\/a><\/div><div class=\"wp-block-file\"><a href=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/105\/vid_lecture04fin.ppt\" target=\"_blank\" rel=\"noreferrer noopener\">Lecture_04.ppt<\/a><\/div><\/div>","protected":false},"excerpt":{"rendered":"<p>Digital sampling of any signal, whether sound, digital photographs, or other, can result in apparent signals at frequencies well below anything present in the original. Aliasing occurs when a signal is sampled at a less than twice the highest frequency &#8230;<\/p>\n","protected":false},"author":40,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":""},"class_list":["post-8","page","type-page","status-publish","hentry"],"acf":[],"_links":{"self":[{"href":"https:\/\/sisu.ut.ee\/imageprocessing\/wp-json\/wp\/v2\/pages\/8","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sisu.ut.ee\/imageprocessing\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/sisu.ut.ee\/imageprocessing\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/sisu.ut.ee\/imageprocessing\/wp-json\/wp\/v2\/users\/40"}],"replies":[{"embeddable":true,"href":"https:\/\/sisu.ut.ee\/imageprocessing\/wp-json\/wp\/v2\/comments?post=8"}],"version-history":[{"count":2,"href":"https:\/\/sisu.ut.ee\/imageprocessing\/wp-json\/wp\/v2\/pages\/8\/revisions"}],"predecessor-version":[{"id":73,"href":"https:\/\/sisu.ut.ee\/imageprocessing\/wp-json\/wp\/v2\/pages\/8\/revisions\/73"}],"wp:attachment":[{"href":"https:\/\/sisu.ut.ee\/imageprocessing\/wp-json\/wp\/v2\/media?parent=8"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}