LCD monitors frame rates

[akis]

I am trying to understand the concept of "screen refresh rate" on computer monitors. Most LCDs do not even mention a figure and they report 60Hz in Windows, what does that mean? Does it mean that each individual pixel on the screen can be switched on and off maximum 60 times per second? Or does it (also) mean that to set *all* the pixels together require a bandwidth which is limited by the rest of the electronics and that determines the effective "refresh rate" - a quick calculation says:

1920 x 1080 x 3 = 6,075 KB per frame

Assuming 60 frames per second, this is a ridiculous 365MB/sec bandwidth over the cable.

I have not looked at this problem before but some questions are:

1) when my monitor says "60 Hz" does this mean that at best there will be 60 frames painted on the screen per second regardless if the graphics card displays for example 100 FPS?
2) What do I gain by buying a monitor that claims 144Hz?

Thanks

[wraper]

Assuming 60 frames per second, this is a ridiculous 365MB/sec bandwidth over the cable.

Can be even more than that. On my 2560x1600@60Hz monitors there is almost 6 Gb/s of raw data bandwidth +25% overhead due to 8b/10b encoding used by DVI/HDMI. Needs dual link DVI cable to use full resolution or Displayport/HDMI 1.4 capable GPU. Twice that bandwidth if I daisy chain 2 monitors over Displayport.

1) when my monitor says "60 Hz" does this mean that at best there will be 60 frames painted on the screen per second regardless if the graphics card displays for example 100 FPS?

Exactly, thats why there is VSINC setting in the games. Otherwise one frame on monitor can contain parts of multiple rendered frames. http://en.wikipedia.org/wiki/Screen_tearing

2) What do I gain by buying a monitor that claims 144Hz?

Monitor which refreshes at such rate, therefore also higher bandwidth over the cable. But all such monitors are TN = crap color accuracy. Those are for gamers so they don't need to enable VSINC as it have some negative performance/lag effects.

[mariush]

The 60 Hz advertised is the maximum supported by the protocol DVI/HDMI AND the monitor at the native resolution.
For example, with single link DVI you can do a maximum of 1920x1200 @ 60 Hz, with dual link DVI you can do more framerate or higher resolution.

A LCD monitor doesn't have to constantly refresh the pixels to maintain them "alive" like CRT monitors used to have to do. However, for simplicity, the video card will stream the full data no matter if the pixels are the same or not.

Some monitors, in particular some very cheap ones with 6bit panels, use some tricks like flipping some pixels between back and forth between some values (dithering) to give your eyes the impresion of more colors .. while the panel can only do 6 bit or about 260k colors, by playing with pixels several times within a frame interval it can fake more colors.


Yes, you have  width x height x 24 bits per pixel x framerate  x  10/8     bits per second going through the cable.  10/8 because there's a error correction mechanism that converts 8 bits into 10, similar to how data is sent through sata cable.

Some 4k monitors recently advertise that they support 60 fps using hdmi or some cheap displayport but it's a trick -  hdmi is not capable of 4k @ 60fps with rgb, so they send yv12 instead of rgb to the panel.
RGB is read green blue, 3 x 8 bits... but it's possible to convert this color into a Luminosity and two chrominance values  which works better for some things because your eyes are more sensitive to luminosity and less to chrominance. With YV12, they take 4 pixels, send the luminosity info for each pixel separately and then do a sort of average of the chrominance information for those 4 pixels - so instead of  4 x 3 bytes = 12 bytes, they only send 4 + 2 = 6 bytes

[wraper]

Some monitors, in particular some very cheap ones with 6bit panels, use some tricks like flipping some pixels between back and forth between some values (dithering) to give your eyes the impresion of more colors .. while the panel can only do 6 bit or about 260k colors, by playing with p

Actually most of the monitors. Most if not all TN, even Low-middle class AH-IPS ones are 6bit + FRC in most cases.

[miguelvp]

Actually 1920 x 1080p @60Hz has a higher pixel clock than that.

There is a back porch then the 1920 pixels then a front porch and Hsync on the horizontal line. VESA standard makes the horizontal line to be equivalent to 2200 pixels across.

Similarly on the vertical, you have a vertical back porch then the 1080 lines then a vertical front porch and then the Vsync, making it 1125 lines worth of signal.

So the pixel clock is 2200 x 1125 x 60 (for the number of frames per second) equal to 148.500000 MHz and each pixel consisting of red, green and blue (sent in parallel via LVDS along with the clock sent via LVDS as well to the LCD.

Edit: Essentially pushing a bit under 425 MB/s (where MB is 1024x1024 bytes) worth of data (or 3.6Gbps if you think of it as network speed where Gbps is 1000x1000x1000 bits per second)

1) when my monitor says "60 Hz" does this mean that at best there will be 60 frames painted on the screen per second regardless if the graphics card displays for example 100 FPS?

Yeah, you won't see the difference, but for games (1st person shooters) an FPS is a game clock tick, so if the game updates 100 times per second your gameplay and reaction to others has more resolution, meaning you can shoot faster or react faster the more FPS the game runs at.

2) What do I gain by buying a monitor that claims 144Hz?

That will let you run 3D games (as in stereoscopic) at 60Hz since it has to draw double the frames plus in between eye blanking. Then again, that will half the game play so you are back to the response time of the game running at 60 Hz.

Some TVs can even do 400Hz and it seems it helps the color rendition but I'm not quite sold on that since I haven't seen one in person. I guess they can interpolate frames to give a smother and more fluid look.

Professional gamers do benefit from higher frame rates, and they develop good timing muscle memory that allows them to do repetitive sequences that gives them an edge, but that is after playing a lot, I mean like any NBA professional played B-Ball on every single waking moment. For your average gamer there is no difference.

[NiHaoMike]

I can tell the difference between 60Hz and 120Hz (both at 1080p) for gaming but it's not enough to improve gameplay by much. I can't imagine 240Hz actually giving a better experience than 120Hz unless you're using 3D glasses, which is probably the main use case. I haven't got to try 4K yet (too expensive) but I highly doubt it would make a real difference for gaming, though it would be excellent for photo editing and heavy multitasking. The GPU requirements to run 4K at 120Hz or more would be really high.

There is also an emerging technology ("time domain multiplexed") of making a very fast monochrome LCD and backlighting it with a RGB LED array, the idea is that by pulsing the colors in sequence and displaying the color subframes, it would theoretically be three times as efficient as regular LCD. (In practice, the power usage of the processing electronics currently makes it impractical for mobile applications where it has the greatest potential, but that's changing...)

[miguelvp]

4K signals are only 30Hz since there is a limitation on the HDMI specification, plus the video card would need to be able to render 8 times faster than 1080p at 60Hz to give you 4K at 120Hz.

Edit: nevermind HDMI 2.0 can do 4k at 60Hz, who knew!

[amyk]

A LCD monitor doesn't have to constantly refresh the pixels to maintain them "alive" like CRT monitors used to have to do.

They do need to be refreshed - each pixel is a capacitor, similar to DRAM. If the pixel clock is too slow the display will slowly fade away (although the timescale for this is far longer than phosphor persistence of a CRT), and there's risk of electrolysis damage to the LC since a DC voltage is being applied to the pixels for too long - this is the primary factor in determining the minimum frame rate. Even the simple non-multiplexed LCDs in things like 7-segment displays and indicators are driven with AC at a high frequency.

Lots of info on how LCDs work is here: http://lcdpanal.blogspot.ca/2008/04/liquid-crystal-was-discovered-by.html

[akis]

After a bit of search it appears that high frame rates (eg 120Hz +) are associated with TN panels. It also appears that TN panels are the worse in terms of viewing angles, colours, and white bleeding. BenQ has a technology called VA for its panels which is supposedly better than IPS.

I also learned that LED monitors use PWM for the backlight which can be perceived/cause headaches. BenQ have direct drive without PWM on some of their monitors.

I have settled on the GW2460HM. I would prefer it in vertical resolution of 1200 but we cannot have everything. This is to replace my ageing but beautiful BenQ 24" which my son destroyed a few days ago. I think BenQs are unpretentious, as other monitors are twice the price for the same or worse stuff. I also read very bad comments on Dell's Ultrasharp 24" and it seems Amazon UK are trying shove them down my throat on every search I do.

[wraper]

After a bit of search it appears that high frame rates (eg 120Hz +) are associated with TN panels. It also appears that TN panels are the worse in terms of viewing angles, colours, and white bleeding. BenQ has a technology called VA for its panels which is supposedly better than IPS.

It have only better contrast than IPS (darker blacks), otherwise it is worse in all aspects. It suffers from "gamma shifting" and "black crush" effects with viewing angle. Can consider it as a budget IPS alternative.

[akis]

I m now reading even more! Luckily I have not yet "checked out" my Amazon Basket. But for IPS, I read in many places about the "yellow tint" that affects them. I also had an IPS NEC at work and IIRC it had some sort of a visible grid on it ?

[wraper]

About 2 weeks ago I searched for cheap non TN ~24" monitor for my father so did some research on current models. That BENQ model is not any better than dell U2412 compared with + dell is in different league as is in more expensive 16:10 aspect rate. Dell often have problems (like software bugs) in early revisions but they are fixed later. BTW that dell is 2 years old model, likely removed from production. New models are P2414H and U2414H. U2414H have wide color gamut backlight and better dead pixel warranty like whole U series. BTW those 'true' 8 bit of that BENQ is bullshit , tests proved that it is 6 pit + FRC panel. New DELLs are PWM free as I know. Anyway it needs to be verified for exact model.
About dell bugs:
I had a custom color setting software bug in my two U3011 rev 01 monitors. Exchanged both of them at the end of the warranty. Recieved U3014 instead. One new and one refub. Free upgrade 
Edit: actually U2414H is standard gamut monitor with WLED backlight but almost covers sRGB color space while most of the alternatives do not. U2413 has GB-LED backlight

[wraper]

Yellow tint on IPS is defect if covers only part of the screen. Otherwise it is a crap calibration from the factory. Second can be tuned by custom color adjustments.

[akis]

The one I was referring to is the U2412M. I have always found Dell, like Compaq (in the 80s) to be very pretentious: very high prices for very little extra in the case of Compaq and for nothing extra in the case of Dell. Those were the days we were receiving crates full of Iyama monitors of which only one in five might work. The days where the Compaq "laptop" was actually the size of a suitcase which I remember had to lug and carry in Paris...

Back to reality, what monitor should I get for my son? Needs to be 24", 1200 vertical would be better, but IPS is £100 extra on VA, and have read so many bad comments. My son is picky and will notice, for example the other day he commented that the expensive Logitech M560 was badly made, because there is no separator slit on the cover for the two buttons so it is harder to click one button while the other one is also pressed down... I would have never noticed that. But I tried it just now and he is right, and depends where you put your finger they can also get stuck.

[wraper]

Well, IPS would be cheap only if sticking with 23.8" 16:9 models. In the result I just bought cheapest 23.8" AH-IPS Phillips for 125 Eur, no reviews were available. Except lousy stand it appeared to be pretty good. With photodiode + oscilloscope measured that PWM has 245Hz frequency. Dells have pretty robust construction along with all possible bells and whistles compared to others. With bung per buck in 24" dell might be not the best. However it greatly changes with 27 2560x1440 and 30 inch monitors (if not considering cheap ones on ebay sent from Korea). Actually there is not so much difference in all 23.8" AH-IPS models as all panels are made by LG and only like 2 models of those panels exists. So Main difference will be mechanical, PWM/No PWM, panel grade (possibility of dead pixels, light bleed), color calibration.

[gxti]

I've had a U2412M since shortly after it came out. It looks amazing, but like many things in life once you find out you can never go back and maybe it's better for your wallet to never find out.

About a year ago I got a ASUS VG248QE 144Hz as my second monitor for gaming, and I love the high framerate, but the colors are so bad next to the IPS. The framerate is really really nice though, even just moving the mouse cursor around feels better. Of course then I needed an expensive video card to actually have any hope of achieving that framerate, so there goes another wad of cash...

One thing I never noticed until I got a 144Hz monitor is that 60Hz displays, even nice ones, have hiccups in their update rate. If you try scrolling continuously at a medium speed through a long document, see if you notice it hitching once per second or so. That's the display, not the software.

[wraper]

I've had a U2412M since shortly after it came out. It looks amazing, but like many things in life once you find out you can never go back and maybe it's better for your wallet to never find out.

So true, sometimes I think it is just ridiculous to have $3k worth of monitors standing on my desk (my mistake was buying LG 30 incher in 2007). And I just feel pain when I forced to use my notebook on trips.

[wraper]

One thing I never noticed until I got a 144Hz monitor is that 60Hz displays, even nice ones, have hiccups in their update rate. If you try scrolling continuously at a medium speed through a long document, see if you notice it hitching once per second or so. That's the display, not the software.

It cannot be monitor just for the reason that GPU outputs constant frame rate. To be true, monitor need to drop frames. About even nice ones, Did you try this monitor on different computer? I've seen such a thing multiple times and all this was because of the computer / particular program issues (especially true for browsers, adobe reader). You can for example use tearing test built in the MPC-HC to verify that problem is not in the monitor, or verify that you have some problem with the computer if tearing will be present. Thou it might require to play with render setting as that test is to troubleshoot MPC own problems.

[akis]

I have tried the "shades of black" test on my 17" laptop Sony Vaio and it seems I cannot see two rows of blacks almost But I know the Vaio screen is not exactly the best.

For me the most obvious problems on the LCD screens are in this order : (1) viewing angles - moving or tilting my head and the colours/brightness changes. (2) Blacks are really darkish greys. (3) White light on the edges of the screen (which develops after a while, months even)

I have posted a question on the hard forums : http://hardforum.com/showthread.php?t=1827766

The reality is that for a 24" the prices are:

TN panel = £110 (around $180)
VA panel = £150 (around $255)
IPS panel = £250 (around $425) excluding the Dell U2412M which has received some very , very bad comments on Amazon (the whole Dell company actually and their shoddy practices).

I know my OP was about frame rates but this is immaterial for us, as the other problems I mentioned above are so much more prominent and important.

[wraper]

TN panel = £110 (around $180)
VA panel = £150 (around $255)
IPS panel = £250 (around $425) excluding the Dell U2412M which has received some very , very bad comments on Amazon (the whole Dell

First of all those amazon prices are ridiculous. Second you compare 16:9 1920x1080 VA with 16:10 1920x1200 IPS according to the price difference (16:10 actually have bigger display area). While direct comparison is 16:9 23.8" IPS (only 5 mm difference) with the same resolution as VA.
Again what bad comments, 4.5 out of 5 stars rating? Or you count bad comments in absolute quantity, not relative to total number?
http://www.amazon.co.uk/Dell-UltraSharp-U2412M-inch-Monitor/dp/B005JN9310/ref=sr_1_1?ie=UTF8&qid=1406419185&sr=8-1&keywords=u2412
And if you are concerned about light bleed or dead pixels, you have more chances to get those in other brands.

For example 24MB35PM 23.8 IPS (even models number says that it is 24 inch class) http://www.amazon.co.uk/LG-Electronics-24MB35PM-23-8-Monitor/dp/B00JKNORQG/ref=sr_1_1?ie=UTF8&qid=1406419899&sr=8-1&keywords=24MB35PM

10 pounds cleaper at ccl http://www.cclonline.com/product/147992/24MB35PM/Monitors/LG-24MB35PM-24-inch-IPS-LED-Monitor-1000-1-250cd/m2-1920x1080-5ms-DVI-D/MON2920/
and that 162/153 GBP price actually is expensive, as here in Latvia I can buy such monitor for 153 EUR = 123 GBP.

or for example 132 pounds http://www.cclonline.com/product/133408/i2470Swq/Monitors/AOC-Professional-i2470SWQ-23-8-inch-LED-Monitor-with-Speakers-250-cd/m2-1920-x-1080-DVI-HDMI-DisplayPort-VGA/MON2598/

[akis]

Hi. thanks for the link, I did not know of that company before. I also had not seen IPS at 1080 and 24", I assumed they were all at 1200, but his one lists as 23.8" so it must have been escaping my filters. And it seems that the IPS price is very close to the VA price. In terms of prices in the UK, especially when we compare with the US, there is a term "rip off britain". Well deserved. There was a time where we used to pay in pounds what the americans paid in dollars for the same items made in Asia somewhere. In terms of Amazon ratings, I have learnt from experience to read the most negative comments even for items that have 4.5 stars, and there you most often find the truth. Always read the negative comments. For exxample I can direct you to two different mice, both of which have 4.5 stars and 1000s of feedbacks. But both mice suffer specific faults, and I had to return all three of them (2 of one type and one of the other). Most of the negative comments had covered those faults, had I bothered to read them. I think that LG monitor looks great, price wise.

[wraper]

In terms of Amazon ratings, I have learnt from experience to read the most negative comments even for items that have 4.5 stars, and there you most often find the truth. Always read the negative comments. For exxample I can direct you to two different mice, both of which have 4.5 stars and 1000s of feedbacks. But both mice suffer specific faults, and I had to return all three of them (2 of one type and one of the other). Most of the negative comments had covered those faults, had I bothered to read them. I think that LG monitor looks great, price wise.

Yet dell will have much more comments than LG for example, therefore there there may be no bad feedback even if issues sometimes exist.
With LCD displays it is hit and miss how good exemplar you will get. It might be perfect or with a huge backlight bleed. Two U3011 + two replacement U3014 had zero dead pixels and only minor backlight bleed in one corner of the one U3014. Otherwise they all were perfect (except firmware bug which were not show stopper).

[akis]

Yes of course you are right. I usually expect to find a 10% of "1 star" comments out of the "5 star" comments. For example if an item has 345 "5 stars" I also expect it to have around 34 "1 star". Try shopping for a HDMI or DisplayPort cable for example. Some items however exceed the 10% so in the above example you'd have 345 "5 stars" and say, 60 "1 stars". Now we are approaching 20%, and this is above the "norm" so you have to read and be careful. The LG http://www.amazon.co.uk/gp/product/B00JKNORQG/ref=ox_sc_act_title_1?ie=UTF8&psc=1&smid=A3P5ROKL5A1OLE whose price has just gone up as I am typing this!!! has no ratings so it is hit and miss. Then I was reading on the Eizo FG2421 http://www.amazon.co.uk/product-reviews/B00GBBDHY8/ref=cm_cr_pr_hist_2?ie=UTF8&filterBy=addTwoStar&showViewpoints=0&sortBy=bySubmissionDateDescending -- I mean would you ever buy this regardless how many positives it might have?

[wraper]

http://www.amazon.co.uk/product-reviews/B00GBBDHY8/ref=cm_cr_pr_hist_2?ie=UTF8&filterBy=addTwoStar&showViewpoints=0&sortBy=bySubmissionDateDescending -- I mean would you ever buy this regardless how many positives it might have?

Why not? I would try to find as much info as I can in other places of course.

Now as an engineer myself, I'm aware how hard it is to get the quality of these larger screens right, and I'd be prepared to cut any manufacturer some slack over subtle display issues, but this was really noticeable, all of the time, no matter what I was doing. It's a shame Amazon doesn't let one post images or I'd attach some of the photos I took of the screens prior to return.

This is applicable to every single LCD display model. Guy just had a bad luck. Of course chance of such bad luck highly depends on LCD panel used and it's grade. And again there are only some real manufacturers of the LCD panels, therefore you buy the same candy in the different wrapping anyway.

[akis]

A friend of mine has brought over his Dell U2412M which he wants to sell to me cheaply, it is old and has no warranty.

I ran some tests and everything is absolutely perfect except : on a totally black background there is a "glow" from the left and from the right. The glow is at its minimum when I am looking head on (but still very noticeable) ; if I move slightly up or down there is more glow coming in from both sides and approaching the centre. This is not white bleeding at the edges, of which there is none.

Everything else seems to be perfect, no "yellow tint" (I am not sure how to look for it but all the colours looked OK).

So the only snag here is the "glow" or reflection if you like, it is as if someone is shining a light onto the screen, depending on where my position is. On my laptop there is none of this, blacks look like blacks.

Do all IPS panels behave like this or do I have a dud?