Input Lag, Or Why Faster Isn't Always Better

mr_sifter writes "LCD monitor manufacturers have constantly pushed panel response times down with a technique called 'overdrive,' which increases the voltage to force the liquid crystals to change color states faster. Sadly, there are some side effects such as input lag and inverse ghosting associated with this — although the manufacturers themselves are very quiet about the subject. This feature (with video) looks at the problem in detail. The upshot is, you may want to test drive very carefully any display boasting low integer millisecond pixel response times."

Comments

Another thing to look out for

[Hyppy]

First, we have to look for monitors with 6bit or 7bit color instead of 8 per channel, now we have to start testing for overdrive voltages? Buying an LCD is becoming a real pain in the arse.

Re:Another thing to look out for

[Elledan]

6-bit TN panels don't seem like such a good idea to me, as the interpolation (rapid cycling of pixels to get the desired colour) used to compensate for the lack of full 16.7 million colours other screens have is (together with the flickering of CCFL backlights) responsible for most of the complaints about LCD screens giving people a headache.

As for the article topic, any screen with an input lag of >1 ms will never be 'good' at displaying rapidly changing images, and will be nearly worthless for rapidly-paced games. Plasma, CRT, SED, FED, OLED... all technologies with sub-1 ms latency. Getting that 15" OLED screen LG will be releasing this year as a monitor may not be such a bad idea. Sure, it's not as big as your 24" LCD, but it will have perfect colours and blacks, extremely low-latency, low power-usage, weigh even less than an LCD, and so on.

Let's admit it, LCDs were just an intermediate technology for displays as margins in the CRT market got lower and lower, while new display technologies which could match or beat CRTs in IQ and other factors were still a while off.

Re:Another thing to look out for

[elrous0]

I've got a LCD panel with 5 ms latency and I don't notice problems when gaming. If you're quick enough to say anything over 1 ms is too slow, you're a pretty hardcore (and quick) gamer. And if you're that good, you're probably best served by a pro setup anyway, not low-level consumer grade shit. But I'm not as twitch quick as I used to be, and my gamertag certainly isn't "Fatal1ty," so 5 ms seems fine to me.

Re:Another thing to look out for

[Cowclops]

I knew somebody would make some gross misstatement like "The human eye only sees at 25 fps anyway"

And for that, here is the obligatory link to 100fps.com

In short, the shortest flash a human eye can see depends on a lot of things. These factors are explained thoroughly on that web site. The tl;dr version is this: The human eye can discern A LOT MORE than 25 fps.

Re:Another thing to look out for

[Mprx]

The refresh rate needed to avoid flicker with an impulse light characteristic display is unrelated to the frame rate needed for perfectly realistic motion quality. Note however that non-flicking sample and hold displays such as LCDs will produce lower motion quality than impulse response displays of the same refresh rate because of the temporal smearing. (see http://www.microsoft.com/whdc/archive/TempRate.mspx for explanation).

Re:Another thing to look out for

[poot_rootbeer]

Buying an LCD is becoming a real pain in the arse.

Perhaps, but buying a CRT was a real pain in the back.

Re:Another thing to look out for

[karnal]

Actually, the issue here is probably more due to the fact that movies are shot at 24 frames per second. 24 doesn't fit into 60 properly, so there will be times where the scene repeats more in one set of refreshes than another. See wiki entry on Telecine, notably telecine judder: http://en.wikipedia.org/wiki/Telecine

With a 120hz refresh, 24 can go into 120 evenly, so you won't see any choppiness.

Response time, contrast ratio, etc.

[morgan_greywolf]

These terms 'response time' and 'contrast ratio' are checklist items. What matters is how the display looks and feels. As long as we continue to insist on checklists as a means of determining what to buy, manufacturers are going to keep using tricks like overdrive to make their checklists look better and better.

At the end of the day, sadly, this means that you can't just look at a checklist when buying an LCD display. You must test drive a model live before considering its purchase.

huh?

[Lord Ender]

The upshot is, you may want to test drive very carefully any display boasting low integer millisecond pixel response times.

First of all, I'm not really sure why that's considered a "upshot." But more importantly, I baffled by the submitters implication that I would have to carefully test an 8ms lag screen but not a 7.5 or 8.2ms screen. Huh?

Re:huh?

[blueg3]

What you really have to watch out for is those -4 ms screens.

same old...

[apodyopsis]

reminds of my time making CDROM drives when we ere chasing 4x, then 8x, then 16x, then...

never mind the fact that the interface at the time could not handle the high speeds were were getting too so they were totally pointless, the effort was still to physically read some data off the outer edge of the disc at the quoted speed so we could sell the unit and keep up with the arms race.

I now purposely buy technology a few years old, just so they can work the bugs out and I can ensure it is fully supported under all operating systems, it is rare indeed that I adopt early.

any technology arms race will promote one specific feature above all others and rarely end up with a device that is fit for market and a well rounded balance of features - though I grant that there are some exceptions.

Re:same old...

[ivan256]

CD-ROMs don't. They use "Zone CAV". It's much cheaper and easier to make a drive spin at a constant angular velocity. Unfortunately that results in higher data rates at the outer edges of the disc, so what drives do is they split the disc up into zones. The disc is spun faster for a zone closer to the center of the disc.

Older CD-ROM drives used straight constant-angular-velocity, and would advertise the fastest data rate (which was at the outer edge of the disc).

The only time a modern CD drive will spin with constant linear velocity is when it's playing back audio in real-time. And even then, many players buffer now, so they use the Zone CAV method anyway.

Reason for input lag

[Rotaluclac]

The reason for input lag is that manufacturers want the on-screen image to quickly change without ghosting. Here, quickly means "in as few ms as possible", not "without delay". So if you see a change only two seconds later, but the change is instantaneous, that's considered good.

To achieve this, the display electronics must know what the next frames look like. So they buffer two or three frames, then adapt the overdrive on a per-pixel basis to the contents of the next few frames.

Pro: smoother video playing
Con: a delay of two or three frames

Rotaluclac

Re:How about plasma displays?

[Who Is The Drizzle]

No, plasmas have near instantaneous response times that are pretty much identical to what you get on a CRT. The issues you get with a plasma is called "phosphor lag" which has to do with the three colors not quite lining up perfectly and it gives you a trailing image of the colors. It's especially noticeable on high contrast edges or if things are moving really quickly. It can be especially noticeable in gaming, but at least IMO it's much less annoying an artifact than the ghosting, smearing, and horrible motion resolution you get with LCDs (and yes they are present even on 120hz LCDs before someone brings that up).

Overdrive only slightly related to input lag

[A Friendly Troll]

Overdrive is commonly used on all types of panels - TN, *VA, *IPS.

It isn't related to input lag as much as the summary would like you to believe. Somewhat, yes, but not that much; also, PVA panels are generally the ones with biggest input lag.

Some *VA panels have an input lag of 3-4 frames, some have only 1; some TN panels have a lag of 1 frame, some have 3. Some panels have overdrive that you cannot even notice, some - like the Dell 2407WHP-HC - will make you want to poke your eyes out.

What's much worse than input lag and ghosting are the eternal marketing races for MOAR BRIGHTNESS!!!11 and MOAR GAMUT!!1ONE, eventually leaving you with a monitor with a *minimum* brightness of 250 cd/m2, happily roasting your eyes out in anything but daylight, and with a gamut so large that skin tones heavily shift towards red, wildly inaccurate colours, and easily-visible fringing when you turn ClearType on (surprisingly, Windows Se7en will have proper low-level wide gamut management and will tone it down to sRGB on request, eliminating all issues; probably one of the few things that are actually good enough in that OS).

When it comes to monitors, HardForum is generally the place you want to thoroughly check out: http://www.hardforum.com/forumdisplay.php?f=78

I'm a CRT holdout (rant)

[Bobtree]

This is one of the reasons why I refuse to buy LCDs for gaming, both on my desktop and for consoles. Other factors include refresh rates, variable resolution, and numerous quality problems (dead or stuck pixels, color reproduction, viewing angle, brightness uniformity, etc).

Given a choice, nobody would prefer to play on a laggy ISP, so it's really awful that manufacturers don't inform about multiple-frame image processing delays on 60hz monitors.

CRT technology is so mature and LCD so comparatively half baked that I'm totally revolted by the general consensus to throw out completely superior performance in favor of smaller form factor (it's not like they're moved often).

I spent months last year looking for a flat panel to buy that I would want to game on, and came up empty handed, so I simply abstain.

I'm currently using a ViewSonic P220f from a friend after my 8 year old Sony GDM f500r was recently retired, both 21". My consoles are on a 34" Sony WEGA KV-34HS510.

When my tubes finally give out in a few years, I'll be looking for something far better than LCDs to replace them with.

OLED to the rescue

[Twinbee]

Ugh, input lagging. To me, this would be an even worse issue than blurring or flicker. Lagging (at least above 30ms) means a 'soupy' cursor, and an end to games which require quick reactions.

I hope this becomes another stat to put on advertising. It's very hard to see unless you hook up a computer and do some testing, so joe public won't care... :(

It's exactly this kind of thing which will make OLED technology win in the end. All the problems associated with LCD (response time, blurring, lagging, contrast levels) will be gone in an instant.