intro
for starters, you should probably read this excellent page discussing the advanced tv problem that was most likely in context of around the mid-1990’s. i unquestionably side with the c.i.c.a.t.s. proposal. the same site also has good descriptions of interlacing and compression. i would also point out that the european pal format is superior to ntsc in every way. i am an american.
interlacing
let’s just go ahead and get this one out of the way. interlacing has got to go. unnecessary legacy analog crap. in the absence of digital compression technology it was a brilliant solution. however, those days are supposedly gone so it should no longer be present. i found a good write up about interlacing and digital compression. here’s the important snippet from the conclusion if you don’t want to read the whole thing:
Interlacing is a legacy compression technique developed in the days of vacuum tubes. With MPEG compression, not only is interlacing unnecessary, it’s actually undesirable because MPEG gives worse results with interlaced input for the same bit rate.
atsc’s supposed highest hd format is 1080/60i which is interlaced (that’s what the ‘i’ means). therefore, it should be ignored like the red-headed step-child it is. there are actually a 1080/24p and 1080/30p versions of 1080 which would be fine, but appear to be ignored by the broadcasters.
i should point out that there is a lot of non-sense going on right now about blu-ray and hd dvd and having 1080/60p output. this is totally irrelevant as the majority of content (movies) will have been shot in 24p (24 progressive frames per second) and then full frames encoded into 30 interlaced frames. therefore you will get the full resolution of someting shot on film without having 1080/60p. the xbox or playstation 3 is a different story since they couldn’t theoretically generate full 1920×1080 at 60 frames per second (fps).
the presence of interlacing for non-legacy formats in atsc is the first signs that the committee should have been fired.
high resolution
in their infinite wisdom, atsc thought it was a good idea to have multiple resolutions (clearly having never setup a tv for your average human). this is one of the key components of high definition. there’s 1280×720 and 1920×1080. these are the number of pixels (dots) that make up the screen. the 2 most well known forms are 720p and 1080i which are 60 progressive frames and 60 interlaced frames respectively. pretending for a second that interlaced and progressive scanning are equal (which they’re not), these resolutions are useless for most peoples televisions. supposedly your average home viewer is about 2 or 3 meters away from their display. i wear glasses so my vision should be effectively 20/20. at 2 meters, i question whether or not i can tell the difference between an hd picture and a dvd. for sure, you can tell a difference between hd and analog ntsc, but that is more due to the switch to digital than bumping the resolution. for most everyone with a 42″ display or smaller, they will not be able to tell the difference. the juice is not worth the squeeze.
i found this article from nhk called future prospects of hdtv: technical trends towards 1080p. it’s interesting and claims that the at 2 or 3 meters for a 33″ 1280×720 is sufficient and for 50″ 1920×1080. this is to sustain the appearance of reality. whatever that means. i used to watch dvds and hd on a 6′ wide projected image from approximately 3m using an 800×600 projector. i could make out the pixels, but only if i was looking for it. if you’re actually paying any attention to what you are watching, you don’t notice the pixels.
as a side note, most movies with special effects and all animated movies were generated at 2k resolution (that’s a computer ‘k’, so it’s a 2048 pixels wide image which is very close to 1920×1080). it’s only fairly recently that some movie production is done with 4k (4096 wide) images. that means if you saw something like “finding nemo” in the theater you were seeing an hd image projected at about 30′. don’t you think it’s enough on your 3′ screen? obviously, film has much higher color depth, but that’s a different issue that hd doesn’t even address.
framerates
films have been 24 fps for quite some time and yet we’re still stuck with 30 or 60 fps. wait, my bad, that’s actually 29.97 (30 * (1000/1001)) or 59.94 due to the addition of color to black and white back in the day. another, apparently unnecessary retardedness hoisted upon us by the ntsc. supposedly, it wasn’t even necessary to screw with the frame rate. who selects these government agencies? i digress.
basically, it’s slightly complicated to convert a 24fps movie to 30fps for tv. europe and other pal countries don’t have this problem. pal is 25fps. by speeding up the video and audio by 4%, they can show a movie. as a bonus, the movie is done 4% faster. the downside is that it’s conceivable to notice a slightly higher pitch to the audio. however, i believe i read somewhere that it’s not as big of a problem now using pitch correction software that makes all those pop stars’ cds sound so good. in my experience, it was noticable on older movies, but not on newer ones.
at any rate, the switch to digital was a great opportunity to either get back in sync with the movie industry or get in line with some other countries that have a better choice. unfortunately, atsc chose the same crap. actually, the framerates were apparently originally literal 30 and 60, but later accepted that 29.97 and 59.94 were ok too. show some fucking backbone.
compression
atsc uses mpeg-2 video compression. it’s just not sufficient for the chosen resolutions and bandwidth. especially since most broadcasters around here are sending out an hd channel and a sd channel. so from the already puny ~18Mbps, the alot ~14Mbps for the hd channel. btw, most dvds are ~9Mbps. higher resolutions never should have been attempted with out using better compression. granted, when a lot of this stuff was going on mpeg-4/h.264 or any of the other modern codecs didn’t really exist in any production capacity which is yet another reason why just switching to standard definition digital would have been a good idea.
across the pond
in england, they have digital broadcast television called freeview. the resolution is the same as a pal dvd (720×576 anamorphic widescreen which stretches to 1024×576) although with a slightly lower bandwidth of like 6.5Mbps. the quality was generally fairly good. they made the correct choice.
conclusion
it generally breaks down like this. the first phase of atsc should have been to broadcast the equal of 2 dvd quality channels. by now, everyone could be watching digital television). instead, not. the next phase could including upgrading the image quality and fixing the framerate issues. unfortunately, not. i would have been all for setting 1024×512 @ 25 and 50fps. the worry shouldn’t be with how old stuff is maintained, but looking to the future. we’ll get to that in another post.
i’m sure this is rambling and not very well organized. feel free to suggest edits.