LCD Video Quality - Whats the problem ?

[Heliospherez]

Having been in the PC industry for many years now.....I have seen a good few makes / models of CRT / LCD and Projection setups.

Recently, I was tidying our loft and found my old 19" Philips Flatscreen CRT - which I thought I would power up and test on my current system.

Once up and running at a decent resolution, I noticed how good various videos played - whether movies / youtube etc. Everything media related just looked so much better and smoother.

Now - I currently have a decent enough LCD (and a few decent video cards to test) - with a good refresh rate and it's running at it's native resolution. So why the problem ? I know it's related to various things - dot pitch/contrast ratio/refresh etc - but why are videos so poorly played on most LCDs in this day and age - when they can disply a still image with better colour / more vibrancy ? Even LED backlit LCD's don't seem to be any better..... videos just don't seem to be anywhere near as fluid or lifelike when compared to PC/web based videos played on a good old CRT.

Are there any settings I can change to improve my LCDs reproduction of moving video ?

 

[smilertoo]

crt is just a better technology for standard res video, the pixels blend into each other more and the phosphor persistance smooths motion out a bit; but its rubbish for high res text.

 

[fish99]

LCDs are very sharp and usually significantly brighter than CRT, and it just brings out all the **** on compressed video much more. They also don't handle motion as well.

TBH if you're talking purely about PQ I'd say a CRT would be ahead by most measures. The main reasons LCDs have become so popular is they're much lighter, they take up much less desk space and look better sat on your desk, the screens are bigger, they don't flicker (lots of stupid people would run their CRTs at 60Hz and complain of headaches), and people think brighter = better, all stuff that has nothing to do with the actual picture.

 

[titaniumx3]

The reason why videos look more fluid on CRTs is most likely to do with the higher pixel response times and higher refresh rates of CRT technology.

- The pixel response time is how long it takes for a pixel to change. LCDs have slower pixel response, and eventhough it has improved greatly in recent years, it is still not as good as CRT (though don't quote me on that). The effect of slow response times is frame blurring and ghosting, which makes it difficult to see what's going on when things are moving around quickly (e.g. fast action scenes in movies).

- The refresh rate is the maximum number of unique frames the screen can display per second. Most LCDs have a fixed 60hz refresh rate, where as CRTs can go a lot higher, up to 240hz or something like that, though most can manage about 100hz at decent resolutions.

The problem with a 60hz refresh rate (as with LCDs) is that movies are shot at 24fps, which means that in order to fit those 24 frames into 60 refreshes without changing the speed of the movie or having incomplete frames (screen tearing), they use something called "pull down", which essentially repeats certain frames of the movie, so that there are 60 frames instead of 24 frames every second. Unfortunately, 24 doesn't fit into 60 perfectly, hence what they have to do is repeat the 1st frame of the movie 2 times, the 2nd frame 3 times, the 3rd frame 2 times, the 4th frame 3 times, and so on - if you do the math, you'll see that 24 frames can be made into 60 frames using this method. As you can imagine though, this results in a constant 'juddering' effect, since the delay between frames is not constant (due to the 3,2,3,2,3, ... repeating pattern), which is especially noticeable in long panning shots in movies.

Because CRTS are capable of going to a higher refresh the juddering effects of "pull down" are significantly diminished or removed completely (depending on the CRT refresh rate).

Fortunately though, many new LCDs are coming out with a 120hz refresh rates and faster pixel response times. When it comes to movies, a 120hz rate is beneficial because 24 fits perfectly into 120 (120/24=5). What this means is that when fitting 24 frames of a movie into 120 sreen refreshes, all you have to do is repeat every frame 5 times (i.e. a 5,5,5,5,5,... repeating pattern). Because every frame is repeated the same number of times, the delay between every frame is the same, which means there is no juddering.

Lastly most LCD tvs can actually change their refresh rate to 24hz, so that you don't need any frame repeating at all, hence no juddering.