Widescreen Gaming Forum

In the FAQ you can read about TFT myths, but the FAQ isn't really killing any myths, because the facts are incorrect.

The biggest myth is the refresh rate. CRT monitors worked with refresh rates because that was how the technology functioned, with the electron gun refreshing the screen rapidly, to cause a steady image to remain on the glass tube in front of you. However, with LCD monitors, this no longer applies. But I hear you say that the setting is still available in the Monitor preferences? Correct, but this is a way to fool your video card into thinking that your monitor isn't dead, and to continue functioning normally. If the LCD monitor told the video card told the video card there is no refresh rate, the video card would simply assume no monitor exists. Once again, there is no refresh rate on the LCD monitor, you would not notice a difference between 60hz and 200hz.

This is actually way wrong. A TFT-panel updates your screen in the same way as the CRT did. You can see difference on 60Hz and 75Hz on a TFT.
Before I begin to explain why, I need to say that it isn't the backlight and the flicker this is about. And yes in theory a TFT could update all pixels individually as the quoted text is informing about.
So what is it about? It is about how much information that gets transferred to your monitor, how fast it can refresh the image on screen.

VGA
First, let's look at the old TFT-panels as you may know they used VGA-connectors as the CRT did and had a built in Analog Digital Converter.
The information inside the cable was running at a given refresh rate, normally 60Hz but most TFT's could do 75Hz too (this is for DVI too).
What happends here is that the ADC is converting your signal and showing it on your TFT. The higher refresh rate, the more information can be shown.

DVI
Okay, let me continue, the case is actually the same with the digital DVI-cables. Even though you're running a DVI cable the signal is still using a refresh rate. The colors for each pixel is represented digitally but the whole screen is still updated in the same classic way as the vga-cable did.
Left to right, top to bottom.
For not making a flame war, check yourself at wikipedia;
http://en.wikipedia.org/wiki/Dvi#Digital

What does this really mean compared to a CRT
Well firstly it means that no TFT on the market can match a CRT running at anything above 75Hz refresh rate since no TFT accepts a faster refresh rate. Secondly it means that the full potential of the TFT isn't used at all.

Why use a refresh rate on a digital panel?
There are two main reasons, bandwidth and backward compability.

Bandwidth
Say for a minute that you had per pixel update and unlimited updates per second. How much throughput would the dvi-cable need? Infinite!

To just make it in raw numbers to you, say that you are running 1280x1024@32bit, this would turn out to 3.75MB per frame, now imagine you are moving around windows on your desktop, this could easily be 2000fps on a modern computer, making the poor dvi-cable output more than 1GB of data every second. Let's check out those DVI specs again;
http://en.wikipedia.org/wiki/Dvi#Digital
3.75Gbit of throughput, that is about 475MB/s.

Backward compability
In the old days when all monitors were CRT, applications (mainly games) heavily relied on timing with the refresh rate. A programmer could know exactly when the next frame were going to be on screen and time it with the output of the graphic card. When this became a standard it was called v-sync.

What is the point of syncing? With moving content on the screen you want every frame to be fully drawn before showing the next. V-sync tells the graphic card when it is okay to put out next frame to the monitor. Without a refresh rate to the monitor this wouldn't be possible.

So why does this matter?
For most users this doesn't matter at all, but for picky gamers this make a difference in speed and shown images per second.
It also applies how to count the TFT-speed. A TFT is at best running at the same speed as an CRT plus the response of the panel.

I don't believe the facts of DVI and VGA cables or your calculations, how do I prove it to myself?
A. Tearing
A monitor that could update per pixel data without any refresh rates wouldn't get tearing, play some games with v-sync forced off and look for tearings and vertical lines.

B. Mouse pointers
Just pull your mouse around in circles on your desktop, try to count how many you can see at the same time. Now increase the refresh rate to 75Hz. You will see less pointers, or rather the updates will be so fast that you can't see as many. If your eye isn't fast, make a friend take a photo on the screen.

To really prove this test, try with a crt and low resolution, this is best seen at 100Hz or 120Hz, there will be ONE pointer.

C. Low refresh rates
Some DVI-devices support lower refresh rates, for example TFT-based beamers and some regular panels. Install powerstrip, force a low refresh rate like 40Hz. Play some fast game like Quake 3 or similar and switch back to 60Hz, you will see the difference.

Lastly I would like to say that this isn't complaints from my side, I really like this site and just want to contribute.
When you write facts you have a great responsibility, don't write "facts" without any sources of information. We need to kill myths!

Thanks a ton for the feedback. We're working right now to overhaul the FAQ, but this information would be good for it's own article.

In this post I just made in another thread...

http://www.widescreengamingforum.com/node/8076#comment-160511

... I pointed to a new FAQ that is being worked on. It largely drops the discussions about TFT vs. CRT and "TFT Myths" as LCD panels are largely considered the default monitor choice.

You can see the new draft here:

http://www.widescreengamingforum.com/wiki/index.php/FAQ_v2

I'd certainly appreciate your input to this new revision, specifically the last section on "Choosing a Widescreen Display." I've already received some feedback that too much focus is placed on response time, since the listed response times are often not credible, and because there is no standard definition of response time or measuring protocol.

Well even though TFT is the default choice I think that consumers should know that a higher refresh rate really is something that would make the TFT better, especially with the lower response rates.

From the latest FAQ

Refresh rate
Unlike CRT which need a constant redrawing of the picture, the TFT's refresh rate isn't so much of importance. This is because the pixels stands still until they are asked to be moved. On TFT you need to look for lower response time instead of higher refresh rates.

As I stated above the refresh rate is at the same importance on TFT as CRT, with the difference that the TFT doesn't flicker at lower refresh rates.

This is actually way wrong. A TFT-panel updates your screen in the same way as the CRT did. You can see difference on 60Hz and 75Hz on a TFT.
Before I begin to explain why, I need to say that it isn't the backlight and the flicker this is about. And yes in theory a TFT could update all pixels individually as the quoted text is informing about.
So what is it about? It is about how much information that gets transferred to your monitor, how fast it can refresh the image on screen.

Lastly I would like to say that this isn't complaints from my side, I really like this site and just want to contribute.
When you write facts you have a great responsibility, don't write "facts" without any sources of information. We need to kill myths!

We appreciate your constructive input and I also agree it needs to be specified more. :)

It was written at a time where framerate was capped at 60hz and its still capped as of today on most screens. Even if you can select a refresh rate at 75hz, it droppes frames still. Some have higher refresh rates, but instead of increased framerate, it uses black frame insertion.
Running a screen at 75 hz can even have a bad effect on your overdrive:
http://www.tftcentral.co.uk/articles/overdrive_at_75hz.htm
75hz refresh rate = 75 fps = false on most TFT screens.

Having a higher framerate as the result of a higher refresh rate would be noticable though. On moving pictures that is.

Unlike CRT's, you don't see that constant redrawing of screen. So you wouldn't see a difference between 60hz and 200hz as long as framerate doesn't come into play.
http://en.wikipedia.org/wiki/Refresh_rate

I agree though, we should clearify this, because a higher framerate on LCD's would be benificial to gamers. But, we also need to have it clear that selecting higher refresh doesn't nessesarily give you higher framerate. In most cases, the screen drops the extra frames generated by the GFX.


Edit: I just notised... :welcome

Actually you can see the higher refresh rate selected on every TFT I've tested so far. Just do my "test" with the mousepointers.

Of course many screens can have negative effects due to faster refresh rates, even without overdrive. I have both displays with and without overdrive at home, still I can see that most displays are able to actually display 75Hz.

Frame rate is not capped at most games mainly because it's a real bad way of programming. Normally it is synced with v-sync in OpenGL or Direct3D-applications. This way it's locked to your current refresh rate, nothing else. Frame rate locking without correct syncing just leads to artifacts and a stuttering game.

If 75Hz equals 75fps depends mostly on your hardware but 75Hz at least enables your hardware to show 75fps at peaks instead of 60.
The screen doesn't drop frames, there is no such thing.
Either you run synced and your graphic card renders at synced speed or less. If you don't run synced your card will output as fast as it can and your display will render parts of each frame instead of a whole. For instance if you are running at 60Hz unsynced and having 120fps, your display will show one half frame at the top and next half frame at the bottom (with some tearing in the middle).

As you said you can't notice the difference between 60Hz and 200Hz on a non moving picture. But in that case we could run 0Hz too without seeing a difference ;)


By the way, the test you linked to:
http://www.tftcentral.co.uk/articles/overdrive_at_75hz.htm
Shows that the panel reacts slower but on the other hand with less artifacts. Still reaction speed is nothing without a fast enough refresh rate.
Overshooting errors is not more fun than ghosting.

Fast refresh rates on a TFT would also be useful to game with VSYNC enabled without killing performance. Do the 100hz/120hz hacks help any on those? or are they fake refresh improvement, as in, not visible from the computer's point of view?

Fast refresh rates on a TFT would also be useful to game with VSYNC enabled without killing performance. Do the 100hz/120hz hacks help any on those? or are they fake refresh improvement, as in, not visible from the computer's point of view?

As far as I've tested no TFT allows forcing refresh rates beyond 75Hz. This is real sad in my opinion.

Actually you can see the higher refresh rate selected on every TFT I've tested so far. Just do my "test" with the mousepointers.

Of course many screens can have negative effects due to faster refresh rates, even without overdrive. I have both displays with and without overdrive at home, still I can see that most displays are able to actually display 75Hz.

Frame rate is not capped at most games mainly because it's a real bad way of programming. Normally it is synced with v-sync in OpenGL or Direct3D-applications. This way it's locked to your current refresh rate, nothing else. Frame rate locking without correct syncing just leads to artifacts and a stuttering game.

I wish this was true, but it isn't. We are not talking about capping framerate in games (though thats what Vsync do), but on the screen itself.

If 75Hz equals 75fps depends mostly on your hardware but 75Hz at least enables your hardware to show 75fps at peaks instead of 60.
The screen doesn't drop frames, there is no such thing.
Either you run synced and your graphic card renders at synced speed or less. If you don't run synced your card will output as fast as it can and your display will render parts of each frame instead of a whole. For instance if you are running at 60Hz unsynced and having 120fps, your display will show one half frame at the top and next half frame at the bottom (with some tearing in the middle).

Follow the links from tftcentral and you can read about the framedrops:

"We found the following:
2 didn´t support 75 Hz and we would have a black or unstable image.
2 said that they supported 75 Hz, but when we measured the time between images we realised that they were in fact at 60 Hz.
Finally, the last two really ran at 75 Hz…partially. In fact the monitors really displayed four images and then skipped the fifth. The sixth one was displayed normally. When we looked at the results, we realised that this skipped 5th image was to resynchronise the monitor at 60Hz. In fact, it really displayed 4 images in 67 ms whether it was at 60 or 75 Hz."
http://www.behardware.com/articles/641-5/1rst-lcd-at-100-hz-the-end-of-afterglow.html

As you said you can't notice the difference between 60Hz and 200Hz on a non moving picture. But in that case we could run 0Hz too without seeing a difference ;)

At 0 hz, the GFX card wouldn't transmit a single picture, so you'll see nothing. At 60hz with a non moving picture, you will not notice any change to 200hz (provided that your screen would accept that refresh and not display out of sync). This is because a LCD doesn't need to constantly draw the picture (CRT's redraw the picture at given refresh rate per second). A LCD, even though it scans progressively, it doesn't change the pixels state as long as there is no change in shade.

By the way, the test you linked to:
http://www.tftcentral.co.uk/articles/overdrive_at_75hz.htm
Shows that the panel reacts slower but on the other hand with less artifacts. Still reaction speed is nothing without a fast enough refresh rate.
Overshooting errors is not more fun than ghosting.

Thats true. Overdrive artifacts (overshooting, wrong shades, negative motion blur etc) are not a pretty sight. :)

Fast refresh rates on a TFT would also be useful to game with VSYNC enabled without killing performance. Do the 100hz/120hz hacks help any on those? or are they fake refresh improvement, as in, not visible from the computer's point of view?

You can get real performance by this. If your machine doesn't achieve 60fps, and you use Vsync, it will be capped at half (30fps). Since Vsync is governed by the given refresh rate, I would think that having a larger refresh rate should make Vsync cap the refresh rate at 50hz (from 100hz).

The black frame insertion given by some of the "100hz" screen have a function. The black frame inbetween the regular frames helps "clearing" your eyes retina, so movment seems smoother to the eye. :)

Yeah that's why I said fake, it helps the viewer just not the hardware. If having vsync on capped it at 30fps and kept it always at 30fps it would be fine to me, probleme is it doesn't, it goes much lower as far as I can tell, even with sli ultra's.