Input Lag and Response Times
We've heard frequent complaints about input lag on various LCDs, particularly after our last review of the Samsung 245T. We decided it was time to take a closer look at the subject and see if we could come up with a repeatable test. We ended up settling on a test similar to what we were using to show response times, with a few changes.
We run the Wings of Fury benchmark in 3DMark03, with the resolution set to the native LCDs resolution -- in this case 1920x1200. Our test system is an overclocked quad-core Q6600 (3.30 GHz) running two Radeon HD 3870 cards in CrossFire on a Gigabyte GA-X38-DQ6 motherboard. (This is the same system used in our initial testing of 3DMark vantage.) We connect the test LCD and a reference LCD to two outputs from the Radeon 3870 and set the monitors to run in clone mode.
The reference Monitor is an HP LP3065, which we have found to be one of the best LCDs we currently possess in terms of not having input lag. (The lack of a built-in scaler probably has something to do with this.) [Ed: Before you ask, no, I do not have any CRTs around that I can use as a reference monitor, and frankly I don't want any. They're huge, heavy, and require more power, and the best ones were made over five years ago. Sorry - LCDs are where everything is heading. R.I.P. CRT.]
While the benchmark is looping, we snap a bunch of pictures of the two LCDs sitting side-by-side. We set our camera to f/2.2, ISO-400, and a 1/400 sec exposure in order to get a clear snapshot of the on screen action. (Note that these settings have changed from previous articles.) 3DMark03 lists a runtime with a resolution of 10 ms at the bottom of the display, and we can use this to estimate whether a particular LCD has more or less input lag in our reference LCD. We then sort through the images and discard any where the times shown on the LCDs are not clearly legible, until we are left with 10 images for each test LCD. We record the difference in time relative to the HP LP3065 and average the 10 results to come up with an estimated input lag value.
It's important to note that this is merely an estimate -- whatever the reference Monitor happens to be, there are some inherent limitations. For one, LCDs only refresh their display 60 times per second, so any measurement less than approximately 17 ms is not 100% accurate. Second, the two LCDs can have mismatched vertical synchronization, so it's entirely possible to end up with a one frame difference on the time readout purely because of this. That's why we average the results of 10 images, and we are confident that our test procedure can at least show when there is a consistent input lag/internal processing delay.
Here is a summary of our results, followed by a sample image chosen to highlight the pixel response time of the LCDs. Despite what the manufacturers might advertise as their average response time, we found most of the LCDs were equal in this area -- they all show roughly a one frame "lag", which equates to a response time of around 16 ms.
| Display Input/Processing Lag vs. HP LP3065 | |||||||||||
| One | Two | Three | Four | Five | Six | Seven | Eight | Nine | Ten | Average (ms) | |
| ASUS MK241H | 10 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
| Dell 2407WFP | 10 | 20 | 30 | 20 | 10 | 10 | 30 | 30 | 10 | 20 | 19 |
| Dell 2408WFP | 30 | 40 | 40 | 40 | 30 | 30 | 40 | 30 | 50 | 50 | 38 |
| Gateway FHD2400 | -10 | -10 | 0 | 10 | 10 | 10 | 0 | 10 | 10 | 0 | 3 |
| Gateway FPD2485W | 30 | 10 | 20 | 20 | 20 | 10 | 0 | 30 | 20 | 20 | 18 |
| HP w2408 | 10 | 10 | 0 | 0 | 0 | 0 | 0 | 10 | 0 | 0 | 3 |
| LaCie 324 | 40 | 30 | 40 | 30 | 40 | 50 | 40 | 50 | 50 | 30 | 40 |
| Samsung 245T | 30 | 30 | 30 | 30 | 30 | 20 | 30 | 30 | 20 | 20 | 27 |
| Samsung 2493HM | 0 | 10 | 0 | 0 | 0 | 10 | 0 | -10 | 0 | 10 | 2 |
 ASUS MK241H |
 Dell 2407WFP |
 Dell 2408WFP |
 Gateway FHD2400 |
 Gateway FPD2485W |
 HP w2408 |
 LaCie 324 |
 Samsung 245T |
 Samsung 2493HM |
The table tells a clear story: all of the S-PVA panels as we mentioned clearly have more input lag/internal processing lag than all of the TN panels. This is a pretty shocking result, as it indicates that the problem may actually be inherent in S-PVA technology, although there are still panels that do better in this area. The Gateway FPD2485W and Dell 2407WFP both have an input lag just under 20 ms -- or a one frame delay on average. The Samsung 245T has a 27 ms delay on average, indicating it would be one or two frames behind what is actually happening. Worst of all are the Dell 2408WFP in the LaCie 324, which have a two or three frame lag. (This is discounting any other lag that is present between the user and what they are seeing on the display; there's also a slight amount of lag associated with reading input from your mouse/keyboard, processing that input, rendering the resulting image, and sending that to your display.) In contrast, the four 24" TN panel LCDs all more or less match the HP LP3065.
Thus, we have no choice but to conclude that if you are seriously concerned about input lag, you will have to sacrifice viewing angles, color accuracy, and/or overall display quality in order to avoid this on the current 24" offerings. On the other hand, we have played games on all of the test LCDs, and we honestly can't say that we noticed any difference in our overall performance. But we weren't hopped up on Bawls and we don't have a 1337 name like Fatal1ty. Competitive gamers will probably feel differently.
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Rasterman - Friday, May 9, 2008 - link
Yeah the figures reported are meaningless, if they were actually useful we wouldn't even need reviews :) I can't believe that a company as big as Viewsonic doesn't send a review site as big as Anandtech a review model, that is just ridiculous, they should be sending you guys a new model of every new monitor without even asking, maybe you aren't emailing the right person. BTW its awesome to see a reviewer actually answer questions and critics to a review, awesome job Jarred!JarredWalton - Friday, May 9, 2008 - link
I'm sure I'm not getting the right person at Viewsonic (and other companies as well), but that's the trick: *finding* the right person. Without an inside contact, it can be tough to get started.Generic PR Person: "AnandTech? What kind of a name is that? http://www.homestarrunner.com/sbemail50.html">Baleeted!" I'll try to meet with them next CES or something....
PS - Anyone from Viewsonic read this? If so, email me! :-)
10e - Tuesday, May 6, 2008 - link
Great review. This is what multifunction fans are looking for. I had this issue a year ago trying to find "THE" multifunction.You may want to mention that in terms of 720p and 1080p the Samsung stretches both to 16:10 with A/V mode off. I tested this and found that problem recently, which was unfortunate due to the fact that I liked it as a high quality TN.
JarredWalton - Tuesday, May 6, 2008 - link
I mentioned this on page 11, but I have highlighted (italicized) the pertinent text. I also clarified by indicating that 16:9 modes will always have the wrong AR. Thanks for reading and commenting!xerces8 - Monday, May 5, 2008 - link
A picture says more than 1000 words :http://www.digitalversus.com/duels.php?ty=6&ma...">http://www.digitalversus.com/duels.php?...2=49&...
(I can't create a link, seems the post javascript is broken, I cant make bold or italics text either, tried FF and IE7)
JarredWalton - Monday, May 5, 2008 - link
You mean, http://www.digitalversus.com/duels.php?ty=6&ma...">pictures like this one? I don't see any large blowups of their comparisons available for download, so I have no idea exactly how they're testing. What I do know is that I provided images showing LaCie 324 and Dell 2408WFP clearly displaying a 40ms delay relative to an HP LP3065, and I've also provided a picture of the ASUS MK241H with a relative delay of 0ms relative to the same LCD.I've got nine other sample images from each of the tested monitors showing the evidence for my "input lag" conclusions. That's about as close to full disclosure as you'll get. All I get on that comparison you linked is a chart that apparently "proves" the ASUS MK241H has a 54ms average delay compared to a CRT, but then the same site lists the Dell 2408WFP as 69ms, the 2407WFP as 24ms, the LaCie as 41ms, and the Samsung 245T at 59ms. I got more or less the same result on the Dell 2407WFP and the LaCie 324, but nowhere near the same result on the MK241H, 2408WFP, and the 2493HM.
Again, you've got at least one clear sample of my results for each LCD. Sorry, but I have to question their results without better evidence.
Dashel - Monday, May 5, 2008 - link
Hi Jarred,Not sure if this is based on the same test or what but there is this:
http://www.behardware.com/art/imprimer/712/">http://www.behardware.com/art/imprimer/712/
Which looks to be the same graph and results. To me your results seem to make the most sense if the 2408 is very similar to the 2407WFP-HC, then the input lag should be close too I would guess. I'm hardly an expert just tryint to be logical.
The thing is I also see anecdotal claims of lag and people who have tested it getting in the 60ms range as well which leads me to wonder if there isnt some sort of defect or difference in some of the panels vrs others.
Example of a test by an owner:
http://www.hardforum.com/showpost.php?p=1032124531...">http://www.hardforum.com/showpost.php?p=1032124531...
I'd love to hear Dells thoughts on it as well as what and when their revision is due to hit.
JarredWalton - Monday, May 5, 2008 - link
I'd like to know what software people are using as timers. I tried about 10 different "timers" and discovered that a bunch are limited to the Windows default timing resolution - about 54ms. So they either scored "0ms" or "54ms" on the delay. I know this because I had screen refreshes where the timer was split in half; the top half would show for example 40.067 and the bottom would show 50.121.3DMark03 at least looks to be accurate down to 10ms - there are again pictures where the timer is cut in half, only in such cases I would see 20.23 and 20.24, so I can be sure that the timer is updated in .01s increments rather than in something larger.
Without a lot more details about what software people use and large images showing the results, I must say that I'm very skeptical. I feel "input lag" testing needs several things to be even remotely acceptable:
1) Run at native LCD resolution in clone mode (because built-in scalers could have an impact)
2) Disclosure of the test software that manages better than 54ms accuracy.
3) You need a high-end camera with a fast shutter speed to capture the results. Simply choosing "Auto" mode and snapping a picture doesn't tell the whole story.
4) Provide at least one sample image at a high resolution that clearly shows what the camera captured.
I met all of those criteria I think. In looking around at other reviews, I have not been able to clearly answer any of those questions. Perhaps that's why some of the other results are so different. I also tested at 2560x1600 to verify that I wasn't hurting the HP LP3065 by running at a lower resolution; since the scaling is handled by the GPU rather than the LCD (the LP3065 doesn't have a scaler), there was no penalty.
DangerousQ - Monday, May 5, 2008 - link
I cant believe this set of reviews is so one sided, why no P-MVA panels, I bought a BenQ FP241W about 3 monyths ago and the 6ms response time plus unbelievable colours make this panel really hard to beat, but you try finding any reviews on it. The one review I did find, a long time ago and have lost it now compared it to the 2407 dell and found it a better panel for less money! I know this cos I was going to buy the dell before I saw the review.JarredWalton - Monday, May 5, 2008 - link
Send me an MVA panel - or get one of the manufacturers to send me one - and I will be more than happy to review it. I don't have the means to go out and purchase $500+ test LCDs, so I review what I get sent. Dell, Gateway, Samsung, ASUS, and other major companies are great about working with review sites like ours. Other companies are not. Thus, I take what I can get.