Showing posts from November, 2020

Dell E198FPb review: input lag and upscaling tested using the piLagTesterPRO

This TN 1280x1024 LCD from 2008 comes from the era of 4:3 aspect ratios and was probably intended for office work. But as it turns out it has very low lag and pretty good response time, showing that display technology has not advanced anything like CPUs or GPUs over the same timespan.  

Overview/Image quality

At native resolution viewed from straight on this LCD looks fine. Because it's a TN display viewing angles are poor when viewed from below, but are fine from the side or above. At native resolution it's pixel perfect, with zero cropping or aliasing, as you'd expect for a desktop monitor. 

Because of it's desktop focus it doesn't support interlaced modes or very many modes at all, really. There's no reason to run it at anything other than native resolution. 

It only accepts VGA input. Because my tests device only outputs HDMI I used an adapter but it didn't seem to hurt the image quality at all, even a checkerboard with 1 pixel squares was displayed with no issues.

Input Lag

This display does not have a game mode. I used a piLagTesterPRO to measure input lag. This device sends a frame of video over HDMI and measures how long it takes to display it.

It supports both 60hz and 75hz. I tested both at a few different resolutions.

Full Test Results 

I report two kinds of values. 1st response measures how long it takes for the TV to start responding (I use a 5% change in display brightness). This overly optimistic value doesn't tell how long it takes to see anything useful, but matches what other reviewers call input lag. full response is a more realistic measure of lag, and requires the display to reach 80% of it's final brightness. This combines both input lag and response time, and is closer to what you would actually experience in a game.

Resolution1st responsefull response1st responsefull responsescan outresponse timert full
1280x1024 60hz3.08.418.622.315.65.43.7
1280x1024 75hz2.77.315.419.712.74.64.3

The input lag is excellent, as is often seen for TN panels, even ancient ones like this, ranging from 2.7 to 4ms. The response time is a more complex story. If you look at the native resolution it's about 4ms, which is very good. But it drops to about 18ms in the other traditional TV modes. The pi encodes those modes for TV output, using a limited range of intensities, ie black=16 and white=240 (out of 255). The LCD is much slower when switching from dark gray to dim white than from 0 to 255. You might think it would be the opposite (faster transitions for smaller brightness changes) but the hardware is optimized for the biggest change, perhaps because that's a common benchmark. In any case, it's hard to say what the "true" reaction time is in the situation that it depends on the precise luminance of the pixels, but it's safe to say that the 5ms black to white transition overstates what you would see in regular use. You can even see this in action: a bar drifting across a gray background leaves a longer trail than on a black (or white) background; see photo taken with a 1ms exposure at right. The white bar persists for almost 3 frames. 

The final thing to notice is that the full response at the bottom of the screen is a good bit faster in 75hz mode than 60hz. This means the LCD really can refresh at 75hz, as reflected in the significantly faster scan out time in 75hz mode. Some displays are advertised as 75hz compatible but actually draw at 60hz and drop frames in order to keep up. Another win for a very old LCD.

Results compared to other displays

To allow quick comparison between many display I've summarized the results across all the displays I've personally tested with the piLagTester Pro.  Min lag is the first response at the top of the screen, real lag is the full response at the bottom. 

DisplayYear madeNative Resnative min lag480i real lag480p real lag720p real lag1080p real lagnative response timenative scan out
Dell U2410 (game)20101080p4.062.228.326.526.56.0016.20
Dell U2410 (sRGB)20101080p20.562.445.
Sony 40VL130 (game)20081080p22.866.349.047.347.39.0815.43
Sony 40S20L12007720p48.490.172.973.49.6014.00
Emprex HD 32022007720p27.0126.
LG 42LC2D2006720p28.354.650.850.46.3015.95
Vizio VO370M20101080p2.583.
Philips 42PFL3603D/F720091080p29.
Samsung S27C23020141080p2.936.636.137.018.2514.97
LG 47LW6500-UA20121080p66.6149.7149.081.780.92.2711.83
Vizio VO22L FHDTV10A2008720p28.
Dell E198FPb20081024p2.739.035.05.0012.70

You can see this display is quite competitive, with best of class input lag. Under ideal circumstances the response time is also excellent. Even when using the more pessimistic values for response time (the "real" lag values for 480p and 720p) it's still one the fastest displays I've tested.  It seems that TN has been a good choice for fast displays for a long time. 


I strongly prefer IPS panels for their accurate color over wide viewing angles. A good IPS display will cost more than a TN display, and will almost certainly be slower. If you are primarily concerned with gaming, however, TN might be the way to go, though of course not every TN display is optimized for low lag and fast response.

Other models

I tested the Dell E198FPb model, which is the 19" version. There appears to be two versions of this panel: the E198FPb and the E178FPb .  Based similarities in their names, specs and release date I suspect that they would perform similarly. 

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