Test pattern exposes more issues with dejudder processing, but does it matter?

Dejudder processing on 120Hz and 240Hz TVs can cause all kinds of artifacts.

We've often complained about the video-like look of dejudder processing circuits like Samsung's Auto Motion Plus (AMP), Sony's MotionFlow, and LG's TruMotion found on those and other companies' 120Hz and 240Hz equipped LCDs. Using a process called Motion Estimation/Motion Compensation (ME/MC), they remove some or all of the judder from 24-frame, film-based sources, producing a look some viewers prefer. For the record, we strongly prefer to leave these modes turned off.

But in addition to that videolike smoothing effect, the processing also causes further image degradation. We've documented numerous such instances, which often appear as halos, trails and other unnatural effects clearly visible in program material, especially during medium to fast movement, such as an actor turning his head quickly during a closeup.

Now a post at HDguru.com by reviewer and industry observer Gary Merson exposes additional artifacts caused by the processing. The artifacts are visible in a video of five LCD TV makers' dejudder-equipped LCD TVs (a sixth plasma TV's wedge lacks the flashing and much of the moire). They appear as unnatural flashes and tears in addition to extensive moire that looks like confused, curving lines. The test pattern in the video originated from a Blu-ray test disc by Spears and Munsil, a copy of which is included with the Oppo BD-P83.

Samsung's dejudder processing is highly adjustable.

Using a few of the 120Hz and 240Hz HDTVs I have in my lab at the moment, namely the the Samsung UN46B7000 and LN52B750, the Sony KDL-46VE5 and KDL-52XBR9, and LG 47LH50 and 47LH90, I was able to confirm the Guru's results using the Spears and Munsil disc played via a PS3 at 1080p/24. The flashing artifacts were indeed visible with the dejudder circuits turned on, and disappeared when they were turned off (the flashes and extra moire can appear subtle in the video, but in person the difference is much more obvious). Interestingly, Samsung's adjustable Custom dejudder shows significantly fewer flashing and extra moire artifacts, to the extent that we didn't notice them the first time around, when the judder reduction control is turned to zero.

The artifacts were entirely absent from a pair of plasmas I had on-hand, the Pioneer PRO-111FD and Panasonic TC-P50V10. From these results and the Guru's tests I think it's fair to speculate that other makers dejudder processing modes, such as Vizio, Sharp, and Toshiba, those of also exhibit these artifacts. I didn't have their TVs on-hand to test at the time of this writing, however.

But does it matter? As usual with test patterns, the most important question is how well their results translate to real world video. The Guru's article says "This translates to a loss of fine detail such as film grain and overall image alteration." I've never noticed such a loss when comparing video processing circuits, but that could be because I'm not looking hard enough.

To find out, I stared hard at a relatively grainy Blu-ray, "Silence of the Lambs," and compared the TVs in my lab with dejudder turned on and then turned off. Frankly, it was nearly impossible for me to tell the difference. In all of the sets I looked at, any given TV with dejudder engaged looked just as grainy and detailed as the same TV with the mode turned off. Perhaps a more stringent test, with more source material and especially larger screens, would yield more differences, but either way I feel safe pronouncing the effects of those flashing dejudder artifacts as "subtle" at best. The same can't be said for the halos, trails and other dejudder artifacts, not to mention the smoothing effect itself.

As the Guru rightly points out, one of the benefits of 120Hz and 240Hz HDTVs is improved motion resolution. Its effects are also quite subtle to our eyes--and those of other testers like DisplayMate founder Raymond Soneira--but assuming viewers want the extra resolution regardless of whether they can actually see it, we laud makers like Samsung, Sharp and Toshiba. Their 120Hz and 240Hz LCDs enable the viewer to disable dejudder and its attendant artifacts while keeping full motion resolution. Other makers, including Sony, LG and Vizio, cannot achieve full motion resolution without dejudder.

CNET's HDTV reviews don't currently incorporate tests from the Spears and Munsil disc, but I have seen these kinds of flashing artifacts before on other test patterns I use currently, such as the Film Resolution Loss Test from the HQV Benchmark Blu-ray and the moving monoscope from the FPD Benchmark Blu-ray used in our motion resolution test (for which the HDguru also deserves credit). I am considering revisions to CNET's HDTV testing procedure for 2010, however, and patterns from that Blu-ray could definitely make the cut.

So I'll ask the same question I asked of motion resolution: do you think tests like this are worthwhile to include as part of every TV review? Or are they just too esoteric, out-of-proportion and potentially confusing to be worthwhile? Let me know in comments.

[gefitz]

Unless you can measure it, it doesn't make any sense to me to present information about things the reviewer sees on such a subtle level. I understand that the word "review" implies "opinion". But, describing something that some viewers see and some don't only provides a level of noise to the factual information I'm looking for.

[ChrisLlana]

David -
Is your strong preference for 24 fps a desire to view a movie at the original frame rate, or do you simply prefer the judder look to a more realistic higher frame rate presentation? Or, in other words, if you were establishing a de-novo frame-rate standard for movies (given the capabilities of modern film and digital cameras, and pretending there is no existing standard), would you choose 24 fps over 30 fps? Do you think the pioneers of motion picture filming would choose 24 fps if not for the mechanical limitations of the cameras and slow lenses and film stock of their time, or do you think they would choose a more realistic higher frame rate given that option? If the motion picture industry completely switches over to digital cameras and projectors (all having multiple frame-rate capability), and decides to adopt a more realistic 30 fps (or 60) as the new standard for movies, would you be indignant? As more people view movies on HDTVs, there would be advantages to adopt a consistent frame rate standard for both movies and television (video), and thereby obviate any need for a dejudder feature in televisions.
Thanks.

[katzmaier]

Good question Chris. For me, it's simply the purist view of seeing the film as close as possible to what the director intended.

Objectively, it's entirely defensible to want to see as high a frame rate as possible--we routinely laud PC games for their high frame rates, for example. Reality itself occurs at a much higher frame rate. But subjectively, a film needs to be in 24p, with all of the judder intact, to seem like film to me.

Now that the technology is here to make and display films at higher frame rates, it's pretty interesting that nearly all directors insist on keeping 24p. I'm sure plenty of impassioned justifications for doing so, and perhaps for the opposite, can be found on the interwebs.

[katzmaier]

And I didn't really answer, but to the extent that I can speculate, yes, if creating a new film standard from whole cloth I would opt for a higher frame rate such as 30 or even 60 (hell, why not?). I don't think I'd be indignant if the industry went higher, but it would certainly take time to adjust.

[ChrisLlana]

Actually, I don't think it's so much directors insisting on 24 fps as production companies and studios wanting to make movies that can be shown in movie theaters with film projectors that only work at 24 fps. For directors, the choice is whether to shoot using film (expensive but traditional) versus digital video cameras run at 24 fps (with each video frame then transferred to one frame of film for distribution to theaters); more and more directors are opting for the latter, which digital cameras are becoming extremely capable. More and more theaters are buying digital projectors, thereby skipping the film step. The studios would like to get rid of film altogether; the cost of making hundreds of prints and shipping them to theaters all across the country (and world) is hugely expensive.

[sav1981]

"Do you think tests like this are worthwhile to include as part of every TV review? Or are they just too esoteric, out-of-proportion and potentially confusing to be worthwhile? Let me know in comments."

In my opinion, tests like this are worthwhile for buyers because of one thing...

Money.

HDTV's are expensive and are considered in investment in entertainment. You want something that you can afford with as many "bells and whistle" included as possible. You may not like dejuddering but I find it that it is one of the deciding factors in purchasing a HDTV. Just go to Best Buy and look at all the people who are hypnotized by this feature. In all honesty, it helps set your TV apart from other TV's that your family or friends may have. I guess you can call it "bragging rights". So if a TV has a feature such as MotionFlow, or TruMotion, or CinemaMotion, or whatever you want to call it, of course a review of this feature is important. Like I said before, MONEY, plays a big part of this. So of course you want to make sure that every feature that is offered be reviewed whether it is dejuddering, internet capable, or 3D.

I hope this helps.

[stynkfysh]

I relied heavily on CNet's review of my LN46B750 before purchasing it and I can tell you I can care less about artifacts visible in test patterns or periodic artifacts that you have to get close and really concentrate on - especially if it can be turned off. It would become a blah blah blah part of the review that would likely make me move on. And I am a tech nerd.

[katzmaier]

gefitz, stinkyfish and sav1981: Thanks a million for your feedback. It's a big help to me to know what actual readers and shoppers care about when I'm deciding what and what not to include in my reviews. I'm always leery of extra tests that don't seem to really matter, and conversely always on the lookout for real-world tests that do.

It get me thinking...maybe it's time for a sort of survey of CNET readers' desires as to what to keep in, what to drop from and what to add to my TV testing. I'll think it over.

[chopin952]

I agree completely that we should strive to reproduce exactly what the director intended. When the source is modified either by lower/raising resolution, sharpening, motion interpolation, color manipulation, audio downsampling, etc.. I feel like I'm missing out on the original intent. That's why I looked for a TV with proper 24Hz implementation, the most natural colors, and motion resolution, with the great help of CNet reviews.

However, one test is missing. For example, the Sony XBR6 (and perhaps XBR9) had a significant problem when in 24p video mode. The image was blurred in box-filter fashion practically cutting the resolution in half. It almost seemed intentional, to perhaps provide a "softer" more natural look (i.e. remove "jaggies"). This greatly turned me off to this TV and I had to return it in exchange for an XBR8 which did not have that problem. This test was missing from the review. Connecting a PC and checking for every line of 1080p is good, but it also must be done for BluRay 24p video. Who wants a blurred image when the source is already perfect digital 1080p?

Thanks for the great reviews David.

[joshdeboer]

Yes, include it in the reviews. Also, maybe include the off-angle degrees at which black level drops off and you lose white level on the LCD panel. I think its crazy how popular LCD's have become, considering they look aweful at even the next seat cushion form center.