Talk:480i

message: Does the 480i standard prescribe square or rectangular pixels for the image?  Perhaps this should be tossed in the article.  Daniel.Cardenas 20:17, 10 June 2007 (UTC)
thread_title:  Are the pixels Square or Rectangular? 

message: The article quotes someone who probably has an illustration of systems A and E. This line should be removed, unless you have the illustration.
720 samples minus 16 is not 704 pixels but 704 samples.  —Preceding unsigned comment added by 97.93.100.36 (talk) 17:45, 28 January 2011 (UTC)
thread_title:  Systems A and E even  

message: So this means analog TV max resolution is either 400*480 interlaced (interlaced means 30 Hz horizontal odd lines and 30 Hz horizontal even lines; this means 240 odd lines @ 30Hz and 240 even lines @ 30 Hz and total 240*30+240*30=28800 horizontal lines per second) or  400*480 progressive (480 horizontal lines * 60 Hz = 28800 horizontal lines per second). I only know, that there is about 3(RGB) * ~411 colums. I imagine what is problem because very hard to find information about number of vertical lines (I calculated about 400*3, because 3 colours, so about 400 vertical red lines).  — Preceding unsigned comment added by Versatranitsonlywaytofly (talk • contribs) 11:07, 14 June 2012 (UTC)
thread_title:  what is number of vertical lines for analog televizors? 

message: Over and over we read the myth that 704 out of 720 leaves room for horizontal blanking--it does not.  Digitization of NTSC is covered in BT.601 and makes it clear that there are exactly 858 samples taken per line at a 13.5 MHz sample rate.  The digital frame starts 'logically' at sample number 0 which is the first of the 720 samples of active content.  Following the final sample number 719, samples numbered 720 through 857 contain the horizontal blanking, color burst, and so forth.  The entire 720 samples are active content, zero of those samples are for blanking or "nominal blanking" or any other non-picture-sampling purpose.  The reason there are 720 is that the analog input signal is expected to be 710.85 samples wide, and it's not entirely certain when it will start.  So a fudge area of 8-ish samples on either side will likely be at black or blacker-than-black level.  This is not imposed, it is an artifact.
All 525 lines per frame are sampled.  Some specs say there are 485 active lines (20 lines of vertical blanking per field) and others 483 active lines (21 lines of vertical blanking per field).  There is a half line at the top of one field and a half line at the bottom of the other field, but an entire line of samples need to be recorded, thus the D1 frame is 720 samples wide and 486 lines tall.  The 4:3 visible picture area is defined as the total line length of 63.555...  microseconds minus the horizontal blanking length of 10.9 microseconds, that being 52.6555...  Therefore, the 4:3 visible picture area is defined as 710.85 samples wide and 485 lines tall.  Not 704, not 720.
It's uncertain why 704 was chosen.  But it's based on post-sampling handling of content to put it on media, it's not related at all to capture of analog NTSC video.  704 is the nearest modulo 16 number to 710.85.  And it is unclear about what to do about the discrepancy between 480 lines (the nearest modulo 16 number to 485/486 lines).  Is it merely coincidence that 704x480 times a PAR of 10:11 is 640x480, i.e. 4:3 DAR?  Is the "true" visible area literally 704x480 for digitally-sampled content, or is the "true" visible area actually the slightly larger box of 710.85x485 (of which the top and bottom have been cropped away)?  It's not that important, really.
What is important is that whatever the content of the DV specification, the reality is that most or all consumer camcorders (but I don't know about consumer DV VTRs recording video line-in) use the ENTIRE 720x480 window as their 4:3 display area box.  So if one transcodes 720x480 DV straight to MPEG2 to make a DVD, it will be stretched horizontally as appearing to the viewer.  Empirical tests with actual consumer cameras and consumer DVD players demonstrates that 720x480 DV rescaled to 704x480 MPEG2 plays with the correct aspect ratio.  (Converting the 8:9 PAR of recorded DV to the 10:11 PAR of recorded DVD MPEG2.)  Since I've not seen the actual DV spec, I don't know whether this is by spec, or incorrect by spec.  
146.115.66.42 (talk) 18:04, 27 May 2013 (UTC)
thread_title:  Pixels and Samples and Blanking