Hello, > *"Adam M. Costello" <opendtv.amc+0+@xxxxxxxxxxxx>* > Sorry if it reappears and you get both.] I got both, but I can not reply from home now. I am on leave because we have a newborn baby girl. I'll also use my vacation to prepare my presentation on wide color gamut for ***The Tech Retreat***. > Mr. Stessen, thank you for your very informative posts to the opendtv > list. I am intrigued by ClearLCD, and especially by a tantalizing > remark you made a while back that we can "have our cake and eat it too", > referring to the tradeoff between 60 Hz flicker and 120 Hz judder. Okay, but 120 Hz (frame repetition) is not perceived as judder, it is perceived as a double image. And a double backlight pulse is equivalent to frame repetition, so it is not the desired mode of operation for moving images. > I'm not in the business, just an interested consumer who is hesitant > to "upgrade" my CRT TV to a display technology with superior spatial > resolution but inferior motion portrayal. Inferior to CRT TV, but still far superior to the movie theater... That is, if at least the frame rate is increased to 50 or 60 Hz. Then the further improvement (to movies) by flashing the image, or by further increase of the frame rate, is modest. It is very noticeable on certain selected images, but not quite so visible on movies that were shot with a long shutter time. > ClearLCD is the only non-CRT TV technology I've heard of that > even attempts to retain the impulse characteristic of CRTs. Well, some plasmas come reasonably close, but not quite, and OLED could do it, and SED certainly promises to do it too. And then there are many variants of motion-improved LCDs: scanning backlight, blinking backlight, black field insertion, grey field insertion, and increased frame rate (to 120 Hz). The latter development is happening very fast, because it is the only solution that does not create a flicker problem. ClearLCD for Europe is a combination of frame rate conversion to 75 Hz and a scanning backlight, but it can also be implemented by 75 Hz and black field insertion. 75 Hz is high enough to suppress flicker, and low enough for existing signal processing. For USA 75 Hz is not a good choice, and 120 Hz is still out of reach, so that is where the adaptive backlight comes in as an easy solution. It does not require any change to the signal processing or the display panel, but it does require a different backlight technology (for higher peak power) and is thus a big inconvenience to the rigid supply chain. > (Is anyone developing scanning LED backlights? > I haven't found anything on the web beyond speculation.) It is not a preferred choice for LEDs, because the required peak power (i.e. average power divided by the duty cycle) makes the LED backlight too expensive. With HCFL the peak power reserve came naturally, so it was an easy choice. This reserve can also be exploited for backlight boosting, as I have explained in our paper 26.4 on the SID 2006. > I guess ClearLCD's solution to the flicker/judder problem is related to > something called "adaptive dual-pulse" backlighting, but I have been > unable to find any details about it. Can you (yet) tell us anything > about that? Have you read paper 54.4 from the same SID 2006 ?! It was presented by Pierre de Greef, who is now with NXP. Pierre has also published an on-line paper in Journal of the SID. > From the name, it sounds like the backlight switches between 60 Hz > scanning (one pulse per refresh) and 120 Hz scanning (two pulses per > refresh, 180 degrees out of phase, so that two horizontal stripes are > illuminated at a time, 1/2 screen height apart), depending on whether > the video currently contains any moving objects that the eye might > track. Not "switching". It is a continuous transition. And in principle it can be done for each of the lamps individually. You'll find my name near the bottom of the list on a recent patent that goes into the details. Wait until it comes out... > When switching from 60 Hz to 120 Hz, does the duty cycle remain > the same (the pulse width is cut in half), or does the pulse width > remain the same (the duty cycle doubles, and the lamp is dimmed to > 1/2 intensity)? The former, because in general analog dimming of fluorecent tubes is not so popular. Even more so for CCFL lamps, analog dimming leads to non-uniformity over the length of the tube. > What is the pulse width (in milliseconds)? At 100% nominal output, the pulse width is approx. 35% of the frame period of 17 ms, so it's approx. 6 ms. Less when dimmed. > When the backlight is dimmed for dark scenes, is that accomplished > by reducing the duty cycle or the intensity? I am so far removed from the end product that I can not make any statements with certainty. But based on the above, you can guess. > If the pulse width is 4ms (I'm guessing based on various imprecise > statements I've found), that's a lot better than a full frame time of > 17ms, but still a far cry from a CRT, where the phosphors have largely > decayed after 0.1 ms and almost completely decayed after 1ms (right?). Reasonably correct, yes, but you are assuming that less is always better. The same assumption is generally made for the response time (2 ms is better than 4 ms, etc.), but due to the sample-and-hold effect that this discussion is about, a shorter response time is irrelevant until you introduce a shorter on-time first. Then, making rhe on-time shorter is only relevant to the point where the motion smear due to integration on the retina of the tracking eye becomes insignificant compared to the motion blur due to integration of moving objects on the light sensitive surface of the camera. Because the typical camera uses a long shutter time (I think typically between 5 and 16 ms), the images themselves are already blurred. That blur does not go away with better displays. So there is a point where the law of diminishing returns applies. > If something moves the full width of the screen in two seconds (which I > wouldn't call especially fast), that's one pixel per ms, so a 4ms pulse > would blur away about 3/4 of the horizontal resolution of the moving > object (versus 16/17 for an always-on backlight, versus almost no blur > for a CRT). Is work underway to further reduce the duty cycle? See above. Further reduction is only relevant for moving images that are sharper than what the typical movie producer delivers. But then you'll also get strobing artefacts, so I doubt that you can convince Mr. Spielberg to go further than in Private Ryan. Cinematographers use motion blur and camera tracking, and depth of focus, as a tool for focussing the viewers' attention on foreground objects. We don't want to deny them the use of their own tools ! So, for the typical moving images, you would have to judge for yourself how large the gap is between the best LCD and a CRT, and whether it is worth to further reduce this gap. I think that with an on-time of 8 ms, the improvement is already the proverbial 80% (of the 80-20 rule). This is probably why we are seeing an explosion of 120 Hz panels (being offered by the panel makers to the setmakers), with static backlights. The signs were all there on the SID, and will probably also be at the next CES. > By the way, why is 60 Hz flicker a problem? I've been watching NTSC TV > all my life, and never noticed a flicker (and still don't). But I can > see the flicker on a CRT computer monitor set to 60 Hz refresh. What's > the difference? Probably viewing angle. Your peripheral vision is much more sensitive to flicker than your central vision, and you are sitting very close to a monitor. Possibly also (peak) brightness, though monitors are usually dimmer than TVs. And content... Good content can make you forget about all the artefacts. Especially moving content. Greetings, -- Jeroen +-------------------------------+------------------------------------------+ | From: Jeroen H. Stessen | E-mail: Jeroen.Stessen@xxxxxxxxxxx | | Building: SFJ-5.22 Eindhoven | Deptmt.: Philips Applied Technologies | | Phone: ++31.40.2732739 | Visiting & mail address: Glaslaan 2 | | Mobile: ++31.6.44680021 | NL 5616 LW Eindhoven, the Netherlands | | Skype: callto:jeroen.stessen | Website: http://www.apptech.philips.com/ | +-------------------------------+------------------------------------------+