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Chilling_Silence
08-04-2008, 01:56 PM
Hey all,

At Uni we were told that apparently CRT-type displays are best for viewing High-Definition movies because they have a higher refresh rate.

I would have gone personally in the LCD direction over CRT or Plasma for picture sharpness and whatnot, plus I personally find it much easier to look at an LCD or Plasma over a CRT for 3-4+ hours.

Anyways, apparently the Refresh Rate is supposed to be whats best for High-Def movies and whatnot.
AFAIK the refresh rate of an LCD is 60Hz +
The framerate of most NTSC High-Def movies is 29.97 fps (half the refresh rate?)

Does this then throw that theory out the window? Or have I missed something a little bit here in-class?

Keen for all opinions / comments / technical input :)

Cheers


Chill.

dugimodo
08-04-2008, 02:09 PM
it's actually a very complicated subject, NZ PAL standard TV's refresh at 50 hz or 100 hz for the better models. CRT monitors refresh at typically up to 85 hz. LCD & Plasma monitors are typical 60 or sometimes 75 hz.

CRT draw the picture across the screen from one side to the other, LCD & Plasma draw the whole screen at once. More important for moving pictures on LCD's is the response time, in milliseconds. If it's too high and the motion on screen is too fast the screen won't keep up and will blur the image - particularly apparent on sports broadcasts.

Also CRT are generally thought to have better colour & contrast ratio's. LCD's are getting better all the time though, and you can't buy a 40" CRT - and couldn't move it without a forklift if you could.

In real life you'd just go into a store and look at the sets in action and choose what you liked better. I have a 40" sony LCD and I'm never going back, but my old 32" widescreen philips CRT TV which I sold to a friend still impresse me when I visit.

GeneralKanos
08-04-2008, 02:33 PM
Yea I agree. And like the lecturer said its all about the refresh rate, tho after playing lans for like 4 hours on a crt, I can use my face as a car headlight and it feels about 40 degrees!

CYaBro
08-04-2008, 09:51 PM
Surely when it comes to HD movies it's all about the resolution that the screen can display?
The dot pitch on a CRT screen (from memory this was .26 or .25 or something and maybe less on a very expensive CRT) would make an HD movie look not so great I would have thought?

Chilling_Silence
08-04-2008, 10:51 PM
I wonder if Uni would let me bring in my Desktop, my 22" widescreen LCD, track down a CRT to use, then play back a short movie trailer on each and compare

Deathwish
08-04-2008, 11:34 PM
Aha! You are that biker dude with the EeePC in my class. I won't say where/what since thats almost too much info online, but does stream 1540 ring a bell? I was the guy that said something like "CRT but its very hard to find and it depends how much you spend" because she did specifically ask what is best for HDTV.

I think the way she said it was a bit confusing but basically, you already know what a frame is. But might be confusing the refresh rate with this a little bit. Refresh rate is when those electrons are shot back onto the screen to provide an updated image. The more times this happens inbetween frames, the brighter and smoother our video looks. EG: If you have say a Blu-ray source which is now recorded in true cinematic rates (which I believe is at 24fps and resolution of 1920*1080p), and play that back on a screen which has 50 hz, each frame will be refreshed twice (well, little more since 50/24 is not equal to 2 but you get the point!). I do believe the lecturer mentioned something about the pixels fading and thats why they get duller when refreshed not as often, that is 100% correct. If you took that same source and played it back on a 100hz crt panel (provided you could find one that will have hdmi inputs and support that resolution - but its beside the point) where each frame is refreshed 4 times before it is changed over, then you will find your video will look alot smoother/brighter, if you had maybe a rugby or soccer dvd, you will see that there is less of that dragging effect when that ball is kicked very fast. I also noticed that text gets a hell of a lot easier to read (especially when its flowing horizontally like on news channels or in credits at the end of a movie etc.).

If you want to see this in effect, pop by to your local hdtv retailer store and ask the salesperson to demonstrate the effects of the 'Motionflow' technology found in the Sony D series panel or in one of Panasonics newer (well its probably a bit old now) Vierra LCDs.

I've been able to play around with this kind of stuff at work/home over the years and have learnt it practically which makes it a hell of alot easier to understand, I suggest you try playing the same movie, maybe from your dvd which might be 25/30 fps and play with your refresh rate on your monitor if you can adjust that. If not, atleast see the effects (hopefully you'll have a sports dvd or action movie) it has with the different panels.

* also I noticed the LCD vs. Plasma data/slides were very outdated. I don't even get why they had on that slide that LCD had to be kept on a table where Plasma was mounted. From what I know, Plasma has always been heavier, and LCD (televisions) have always had some form of mounting system available.

Deathwish
08-04-2008, 11:53 PM
I wonder if Uni would let me bring in my Desktop, my 22" widescreen LCD, track down a CRT to use, then play back a short movie trailer on each and compare

Would like to see that ;) Oh yeah, forgot to mention, there is something called a Response time on LCD's which I can't quite figure out how it relates to the topic, I am sure this also has a major factor in the CRT vs. LCD/Plasma for best quality HD viewing. I know that on LCD monitors it can get as low as around 2ms which apparently completely eliminates the ghosting effect which is very undesirable (blurring images and oddities around edges of images on the screen) , and that LCD Tv's have 8~12ms response rates. Im going to have to do more reading on this topic though. It could be that by now, some of the better LCD's (thinking Sony X series) have pretty much caught up (except I think they still cant do the colour range CRT can) but its just difficult because we cannot compare those two side by side since a comparable crt is almost impossible to find in the NZ market.

gary67
09-04-2008, 06:48 AM
Decent article in this months consumer mag on LCD versus Plasma TV's, although not out in the shops yet.

Chilling_Silence
09-04-2008, 09:04 AM
Yeah my families Samsung LCD-TV has a refresh rate of 50Hz. Am yet to see a TV myself that's not Plasma / LCD that takes High-Def input (But I dont look behind every single TV screen), and most of the CRT monitors that Ive used cant get up to 1920x1080, maybe 1600x1200?

So basically, because its being refresh roughly four times per-frame if we're looking at a 100Hz device, or twice per-frame if we're looking at a 50Hz device, it looks better than the LCD which doesnt?

Yeah you're right about response times, our TV has 8ms AFAIK, and my PCs LCD is 5ms.

Off to go download a movie trailer I think :D

Sadly, I doubt my EeePC can play High-Def resolution movies :(

handya
09-04-2008, 10:19 AM
is there even a crt screen that can display 1920*1080 other wise the refresh rate is point less

Chilling_Silence
09-04-2008, 11:11 AM
Im sure that some can. When I was working for IDG back in the day there was some 23" CRTs (HUGE buggers...) and they could do some insanely high res that the graphic designers used. Not sure on exact specs though, but a quick Google should show that some can :)

riscpc
10-04-2008, 04:17 PM
Perhaps I can put my 2 cents worth in. The new Zealand Standard for the PAL system we have is transmitted at 25 frames per second. Each Frame is scanned twice to give a 50 cycle flicker rate. The motion Picture industry show all films on the screen at 24 frames per second. However a dual bladed shutter in the projector shows each frame twice thus making the flicker rate 48 cycles. In New Zealand PAL 625 line system, the film which was shot 24 frames per second, is simply speeded up to 25 frame per second. The reason is Historical in as much our Main frequency is 50 Hertz (cycles per second) and early TV stations used to use the mains frequency to lock their synchronizing pulses to and hence we got a 25 frame 50 field rate. The scanning method used is called inerlaced scanning. As each frame is scanned twice, it is broken into the two fields. Field one scanes lines 1, then 3 then 5 etc and at the end of the scan, the spot flys back (hence the term flyback) to the top of the picture then begins to scan all of the even lines. ie lines 2, 4, 6, 8 etc. At the end of the two fields, one complete frame has been scanned.

Now while it is a 625 line TV system, in New Zealand, 50 of those lines are used for what is known as blanking and contain all manner of signals such as sync pulses and teletext information. That leaves 575 lines left for picture. In fact, the maximum real resolution you can get from a Digital picture as transmitted from Freeview Satellite or from Terestrial Analogue transmitters is 575 pixels and that is all you can get from a standard TV signal digital or analogue.

Hi Definition pictures are different and use a different method of obtaining a better and clearer image and higher definition. Also, there are two types of image displays. Ther is 1080i which is an interlaced picture, usualy with a 100 hertz flicker rate and the 1080p which is a progressive scan. The interlaced one is the same as for the analogue one except that instead of there being 576 lines, all told, there are 1080 lines. I am unsure if any are used for blanking in that HD system. However the interlaced picture is at a 100 HZ flicker or field rate.

Remember the film has to be shown into the telecine machine (for dubbing film to TV recorders) at the film frame rate of 24 or 25 FPS (frames per second). This is translated to whatever frame/filed rate necessary to display the picture at the desired rate on the panel. CRT receivers do have 100Hert'z technology too of course as invented by Philips some years ago.

Now the americans use 60Hertz for their mains supply and historically their TV system used their mains for sync generation too. and so they got left with TV sets that run at 30 frames per second and a field rate of 60 fields. To do that a special projector was needed to show one frame twice and the next frame three times then teice so they could build up the frame rate from the 24 of the film to 30 of the TV system. It sort of worked.

But with LCDs, they still have to convert it to the new frame rate but using frame stores and memory chips, they can do it easily. The film is still projected at 24 frames per second if the show is originating from film but in America, they are able to use something called Progressive scanning. This is where each frame is scanned in sequence of line 1,2,3,4 and so on to the full frame. ie. It is not interlaced and hence a 1080p HD display is denoting that it is a progressive scan.

There are other considerations too when playing from DVD. Standard DVD players still only produce a maximum line rate of 576 in our PAL system. Blue ray 1080 lines. The line rate for HD from TVNZ High Def is 720. I don't know if they are doing it as 720p or 720 i or allowing the receiver to sus out which as most HD receivers can display either. That is the basics of it all, the detail might differ a little.

Hope this helps,

John