{"id":1580,"date":"2011-10-03T16:00:58","date_gmt":"2011-10-03T23:00:58","guid":{"rendered":"https:\/\/www.reenigne.org\/blog\/?p=1580"},"modified":"2011-09-28T14:09:34","modified_gmt":"2011-09-28T21:09:34","slug":"what-is-the-cga-aspect-ratio-exactly","status":"publish","type":"post","link":"https:\/\/www.reenigne.org\/blog\/what-is-the-cga-aspect-ratio-exactly\/","title":{"rendered":"What is the CGA aspect ratio exactly?"},"content":{"rendered":"<p>Somebody asked on the <a href=\"http:\/\/www.vintage-computer.com\/vcforum\/showthread.php?26772-Proper-Aspect-Ratio-Measurements-on-an-RGB-Monitor\">Vintage Computer Forums<\/a> about what the CGA aspect ratio is supposed to be. The answer is usually given as 4:3 (pixel aspect ratio of 5:6), but I was inspired me to find out what the relevant standards say it ought to be, exactly.<\/p>\n<p>The relevant standard in question is SMPTE 170M - composite analogue video signal (upon which CGA is based). This gives an aspect ratio of 4:3, but that is for the full composite picture which 242.5 lines rather than the CGA's 200. The width is given in terms of timings - 63.556 microseconds per scanline total minus 1.5+9.2 microseconds for the blanking period, with a tolerance of +0.3\/-0.2 microseconds, so between 52.556 and 53.056 microseconds altogether. Since the full horizontal period consists of 455 CGA low-res pixels horizontally, the full NTSC active area is the equivalent of (376.25-379.83)x242.5 CGA pixels. Re-arranging, that gives us a screen aspect ratio for CGA of between 1.362 and 1.375 - slightly wider than the usually quoted value.<\/p>\n<p>However, no TV or composite monitor of the time was manufactured to have aspect ratio tolerances as precise as 3% - 4:3 would have been well inside the error bars.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Somebody asked on the Vintage Computer Forums about what the CGA aspect ratio is supposed to be. The answer is usually given as 4:3 (pixel aspect ratio of 5:6), but I was inspired me to find out what the relevant standards say it ought to be, exactly. The relevant standard in question is SMPTE 170M [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4,38,23],"tags":[],"class_list":["post-1580","post","type-post","status-publish","format-standard","hentry","category-computer","category-emulation","category-video"],"_links":{"self":[{"href":"https:\/\/www.reenigne.org\/blog\/wp-json\/wp\/v2\/posts\/1580","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.reenigne.org\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.reenigne.org\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.reenigne.org\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.reenigne.org\/blog\/wp-json\/wp\/v2\/comments?post=1580"}],"version-history":[{"count":1,"href":"https:\/\/www.reenigne.org\/blog\/wp-json\/wp\/v2\/posts\/1580\/revisions"}],"predecessor-version":[{"id":1581,"href":"https:\/\/www.reenigne.org\/blog\/wp-json\/wp\/v2\/posts\/1580\/revisions\/1581"}],"wp:attachment":[{"href":"https:\/\/www.reenigne.org\/blog\/wp-json\/wp\/v2\/media?parent=1580"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.reenigne.org\/blog\/wp-json\/wp\/v2\/categories?post=1580"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.reenigne.org\/blog\/wp-json\/wp\/v2\/tags?post=1580"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}