Samsung HP-T4254 Plasma TV: input lag and upscaling review tested using the piLagTesterPRO

This 720p Plasma TV from 2008 is pretty unique and has a mix of good and bad features; unfortunately the lag is pretty high. It used to retail for about $1500. 

Overview/Image quality

720p 1x1 checkerboard

This is a plasma TV, which generally means at least the following: nearly infinite viewing angles and jaw dropping weight. Both are true in this case as well. The 42" model weights 73lbs. 

At the supposed native resolution (720p) this TV crops 20 pixels off the top/bottom and 40 off the sides. 480p/i crops 20 pixels off all sides. Both modes have aliasing too, particularly 720p, though I've seen worse (see example at right). There's really no excuse for aliasing on a plasma TV: you know the panel was designed specifically to be a TV. Why not hit 720p exactly?  In fact there's only one mode that is pixel perfect: 1024x768, over the VGA connector. So I suspect that's the actual native resolution. 

As for 480p/i, with 42" to play with they could have at least offered a zoomed out mode with black borders and 1:1 pixel mapping. But no such luck. There are zoom/stretch options to crop and/or stretch but none that give zero aliasing and cropping.

Burn in is a common concern on plasma TVs but I saw absolutely no evidence of it on this set, so I'm guessing Samsung solved that problem.

It has all the standard inputs, including 3 HDMI, VGA, and 2 yPbPr. HDMI does not support 480i, only 480p. 

Measuring Input Lag

This display does a game mode, accessed under general settings, not picture. But it does not change the lag any, so I guess it's just for marketing. In fact I toggled all quality settings and none changed the lag. 

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. I measure at the top and bottom of the screen, but as it turns out these produce the same results: the entire frame updates at the nearly same moment, top to bottom. Complicating things significantly, this TV is yet another display that does not actually sync to the input signal - instead it fills its own internal frame buffer from the video input and then draws that when it feels like it. If that sounds glib, it's not entirely: Over HDMI it doesn't seem to draw at 60hz or even 59.94hz, but perhaps a couple hz slower. Thus the amount of lag is constantly varying, for instance in 720p it ranges from 66ms to 74ms, and every second or so it drops an entire frame. I consider this to be a very poor design choice, especially since it only behaves this way over HDMI. If you plug it in over VGA it seems to come close to 59.94hz, which means that that it "only" drops a frame every 4 or 5 seconds. I say only but this is pretty disappointing for a TV that was sold as a premium set. 

Interestingly, the range over which lag varies is only 8ms when plugged in over HDMI; for most TVs that don't sync the variability is a full 16ms (one frame). Meanwhile, when plugged into VGA it is 16ms, what you see, for instance 1024x768 gives lag values that drift from 60ms to 76ms. So VGA input is treated very differently.  Note that the average lag is no better in VGA vs HDMI, and only a few video modes are supported, so I wouldn't recommend it.

Because lag varies over time, I've elected to report the average lag values here, since that seems fairest, but there's no right answer; for more discussion of this issue see the above link.  

Full Input Lag 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 full brightness. This combines both input lag and response time, and is closer to what you would actually experience in a game.

	top		bottom
Resolution	1st response	full response	1st response	full response
480i	88.1	93.1	89.1	94.1
480p	70.0	75.0	71.0	76.0
720p	69.7	74.7	70.7	75.7

This TV updates every pixel nearly simultaneously, from top to bottom, with at most 1ms more lag at the bottom - but due to the drifting lag it's hard to tell, it could be truly simultaneous. That's one the neat things about plasma displays, and why you really need to compare lag at the bottom of the screen to see how a plasma compares to a traditional LCD. The response time is also very low, around 5ms. 

Unfortunately, all that unique plasma tech can't make up for the fact that the set has a very long lag before it starts drawing at all - 70 ms. So this isn't a good gamer set, unless you just play RPGs and the like. 

Results compared to other displays

To allow quick comparison between many displays 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. The min lag value is really unfair to this set, because it ignores the instantaneous update of the whole screen. I'm sorting here by 720p real lag; but even so this set is near the bottom of the list. 

Display	Year made	Native Res	native min lag	480i real lag	480p real lag	720p real lag	1080p real lag	native response time	native scan out
Dell U2410 (game)	2010	1080p	4.0	62.2	28.3	26.5	26.5	6.00	16.20
Panasonic TH-58PE75U	2008	720p	28.0	34.0	34.0	34.0	34.0	6.00	0.00
Dell E198FPb	2008	1024p	2.7		39.0	35.0		5.00	12.70
Samsung S27C230	2014	1080p	2.9		36.6	36.1	37.0	18.25	14.97
Vizio E470VL (vga)	2011	1080p	22.0		39.0	39.0	39.0	9.00	8.00
Dell U2410 (sRGB)	2010	1080p	20.5	62.4	45.0	43.1	43.1	6.13	16.13
Vizio VO370M	2010	1080p	2.5	83.0	49.0	47.0	24.3	5.47	15.67
RCA L40FHD41	2010	1080p	20.3	65.0	48.0	47.0	46.0	9.68	16.63
Sony 40VL130 (game)	2008	1080p	22.8	66.3	49.0	47.3	47.3	9.08	15.43
Polaroid FLM-373B	2007	720p	28.0	82.0	49.0	49.0	49.0	7.00	14.00
Emprex HD 3202	2007	720p	27.0	126.0	51.0	50.0		8.50	15.00
Philips 42PFL3603D/F7	2009	1080p	29.0	84.0	50.0	50.0	50.0	5.00	16.00
LG 42LC2D	2006	720p	28.3	54.6	50.8	50.4		6.30	15.95
GPX TDE3245W	2016	720p	28.0	102.0	51.0	51.0	51.0	8.00	15.00
Sony KDL-46EX400	2010	1080p	28.0	87.0	52.0	52.0	52.0	8.00	16.00
Vizio VO22L FHDTV10A	2008	720p	28.0	94.0	61.0	61.0	61.0	18.00	15.00
Sony 40S20L1	2007	720p	48.4	90.1	72.9	73.4		9.60	14.00
Samsung HP-T4254	2011	1080p	69.7	94.1	76.0	75.7		5.00	1.00
LG 47LW6500-UA	2012	1080p	66.6	149.7	149.0	81.7	80.9	2.27	11.83
Vizio E470VL (hdmi)	2011	1080p	69.0	128.0	95.0	95.0	86.0	9.00	8.00

It's interesting to consider that the top performing TV on this list is also a plasma TV, and meanwhile this one is near the bottom. So don't get obsessed with the tech; pay attention to the empirical measurements instead!

Conclusion

These days there are a lot of cheap plasma TVs on the used market. But all plasma's are not the same. This one in particular is to be avoided. I don't have any other Samsung LCDs to compare against, but it's not a good sign that a $1500 TV of theirs performed so poorly, so I'd avoid other sets from that era as well unless there are published lag numbers. 

Other models  

I only tested the HP-T4254. There's also a HP-T5054, which is probably the same set but with bigger pixels, but I've made no effort to confirm that. A single service manual covers those two models and also the HP-S4253, which suggest significant shared hardware, and perhaps similar input lag as well.