LCDs and game frame rates

[Hender]

I've been shopping around for a nice 18" LCD for the last four years or so, watching the price drop from $3000 to $1500 to now under $1000, and next year I'll probably be ready to pick one up. Yeah, I plan ahead and do my research.

Anyway, I read an article over at Cnet today about the new Geforce4Go mobile chip, and in the article the author describes the chip as such:

"Now for the bad news: Most of that power's wasted on a notebook because the fastest LCDs have slothful response times of 25ms or so. Obviously, when you divide that into a second, you get a screen redraw rate of no more than 40 per second. Forget those 60Hz or 70Hz ratings you see in the specs for LCDs; that's the type of signal they can sync to (another great marketing practice from the industry that brought you 19-inch displays with an 18-inch viewable area). The bottom line: You'll never see those 140 frames per second (fps) except with an external CRT."

Now that just doesn't make sense. Is this indeed how an LCD works, that the screen can only be redrawn at the rate specified by the response time? I looked at the LCD I'm interested in (the LG Electronics L1800P 18.1" active matrix TFT display), and it has an average response time of 50 ms, which according to this author's math, means that no matter what I'm doing, whether it be a game or a movie, I'll be stuck at 20 fps (1000 ms = 1 second, 1000 / 50 = 20)? This doesn't sound right to me. Am I misinterpreting the author and getting my math wrong, or is he way off base with LCDs and response time?

FYI, the original article can be located here.

 

[Gunbuster]

Cnet is having a good day when the reviewer lists the laptop specs. without error

 

[Hender]

Yeah, I know that Cnet is frequently full of crap, but sometimes they get lucky.

Anyone?

 

[tornadobox]

i'm currently using a Samsung SyncMaster 570vTFT LCD on my computer...I'm sure it has a poor response time. Anyway, I play Half-Life and other games on it all the time, and I don't notice any difference from my CRT (except that the LCD has slight occasional ghosting and the CRT doesn't). Basically, my games aren't choppy at all (framerate displays at around 100fps when i ask the game to show it). Now, I know that I'm probably not getting 100fps shown on the LCD, but I can't really tell the difference (after about 60fps you can't really tell a difference anyhow).

i think i'd definately be able to see it if i were getting below 30fps, and frankly, it looks smooth as silk to me.

 

[gdawson6]

LCD's are only good for saving space. Flat Screen CRT's are still much nicer looking.

 

[andrey]

First of all, LCD monitors dont' exactly have the "refresh rate" which we associate CRT monitors with. LCD technology is mostly based on "pixel refresh rate".

In that case, the most important feature of an LCD monitor for gaming will be therefore the pixel refresh rate. Basically, the lower, the better. This will be very similar to refresh rate on monitors, except it has a twist. On standard CRT monitors, refresh rate applies to how many times per second the screen is updated with a new picture. For example, 85 Hz means the screen refreshes 85 times per second. The higher your refresh rate is set to, the smoother moving images will look on your screen.

Pixel refresh rate simply takes this concept and applies to each individual pixel of an LCD monitor. How fast each individual pixel can change its signal from red, green, or blue to another one of those three colors. If the pixel refresh rate is too low, you'll see "ghosting" on the screen, which gives the monitor a blurred effect. As there can be multiple million individual pixels on particular LCD screens, getting each pixel to switch faster can be a big task. Switching pixels called response time. Usually if monitor has response time less than 20ms, you will not see ghosting of images at all during fast moving games.

I hope this expains the situation.

 

[Yoshi]

I use a Planar 18.1" TFT LCD display with a PNY GeForce3 200 Ti video card with the DVI connection.

The Planar, like most other LCD's in its class, is rated for a 50ms pixel response time. The hardcore gamer might argue that this is too slow for high action FPS games. In my experiance things seem to move more than fast enough. I just recently finished the single player mode in Medal of Honor Allied Assault with no complaints. The Planar display shows no evidence of ghosting or choppy frames.

Besides that the Planar LCD is great for everyday use compared to my old CRT, not that I had a top of the line CRT. Anyways, text is sharp and colors are very rich and vivid.

No comment on the guys at CNet.

 

[Dufusyte]

"Response Time" is the time it takes for the pixel to turn from one shade to another. It varies depending on what shades you are switching to/from. The "spec" lists the case of turning from White to Black and back to White. Other shades might take longer or shorter. As you can see, "Response Time" is a somewhat fuzzy spec.

"Refresh Rate" measures how often the screen will provide new data to the pixel: "Pixel, you need to switch to White! Pixel, nowyou need to switch to Black! Etc." If the Refresh Rate is 60hz, it means the LCD is sending out these commands to a pixel 60 times per second.

As you can see, if the Response Time is slower than the Refresh Rate, then the pixel will receive commands faster than it is capable of acurately fulfilling them. For example, the pixel might receive the command to switch to White, then Black, then White, but if the response time is slow, then while it is in the process of executing the switch to black, it will receive the next command to switch to white, and so then it will start switching to white without ever having fully completed its switch to black. The result will be a moment of gray.

So, in some extreme cases, what you would get is "imperfect colors" or a muddied look during fast action. The pixels are receiving commands to switch to various shades but are not capable of correctly presenting that color fast enough before it receives the command to display the next color.

For games, you will still be able to see 60 fps if the refresh rate is 60hz., but if the response time is slow, the colors will look muddied during fast action.

 

[eno]

This might not be what you are looking for but with my CRT monitors I was wondering why the refresh rate of my monitor put a cap on my fps. They answered a "vertical sync" setting in OpenGL. It basically syncs every frame to every cycle of your monitor. Meaning if your card can get 140fps and your monitor only 85hz refresh then It would match it to 85fps. So i went into the NVmax program and turned it off. Now I got 99fps instead of 85fps. But the objects were looking weird and edgy. I believe the term is called "tearing" but what ever it is I turned VS back on and use only 85fps and looks much better. So I would think that since LCD monitors usually have less refresh per dollar ratio that if you wanted to use the "vertical sync" feature you would get less FPS. This is based only on my limited knowledge and my tests using the different settings. Forgive me if I am not correct to all you experts but its just how it looks and seems to me.

Did this help or did you already know this?