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Plasma display, native resolution and internal scaler: what happens to HD video?

817 Views 12 Replies 7 Participants Last post by  jlm
Let's say the panel has a native resolution of 1024 x 768 and a 1080i or 720p HD video is routed into the panel via the vga or component HD inputs. What happens to the HD video signal? Is it acted upon by the internal scaler of the plasma device that takes signals and scales it to the native resolution of 1024 x 768?

What would happen if the HD video is displayed as is without scaling algorithms? 1920 x 540p or 1280 x 720p into a fixed panel of 1024 x 768 or other type? What would happen as the native resolutions of these panels don't match the HD video resoluions?

It must not be a problem as there are plasma users watching HD TV!
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All inputs at all resolutions go through the internal scaler, irrespective. The search for the "magic" input resolution that perfectly matches the native number of pixels is a complete waste of time since the panels all scale all the time anyway!

Only when we have DVI outputs and DVI connected panels will there be any incentive to match up resolutions.


so chippy, is there a loss of resolution when one is sending a 1080i or 720p HDTV signal into a PDP at a native resolution of 1024 x 768? Howabout those 1024 x1024 panels or the 1366x 768 panels?

resolution for the display will always be the native res; for the pioneer, eg., that is 1280 x768. this is independent of input.

there are basically two situations regarding vertical resolution (number of horizontal lines of pixels)

if you send the plas an image that contains less than the native res, 480i or 480p or 540p for example, first the signal is de-interlaced if required and then the scaler in the plas executes its function which is to interpolate and create information to fill in the gaps between input points and display pixels. what is finally displayed is 768 lines of pixels

if you send the plas an image that contains more than the native res, 1080i for example, the plas first de-interlaces and then scales that to match the native res. If you had 720p for the HD signal, that would get scaled to the plas rate of 768 (for the pioneer) or 600? (for the 42" plasmas).

i think the 1024 line displays (Sony) don't really have 1024 lines but use some sort of trickery...they require a different measure for true resolution.

the goofy part is if you take a low res NTSC image, for example and blow it up to fill a 50" plas 1280x768, you have a lot of artificially created pixels in the image, so you get more of what is already poor enough.
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Which raises the question of what happens to 720p or 1080i HD when it is sent to a 42" plasma with a native resolution of 848x480 (like the Panny 42"). Obviously, the Panny's processor downconverts the image to the native resolution -- but how does this explain why the picture is so amazingly good?

One explanation I've heard is that the HD signal has much more information, particularly in terms of color depth, and that this extra information allows the panel to display a much better picture. In other words, there is much more information per pixel than with a standard-definition NTSC signal. It's analagous to adjusting your computer display from 16 bit color to 32 bit color.

Is this a gross simplification? Totally incorrect? Or close to the truth?

One thing is certain -- the HD image on my 42" Panny is simply amazing, nothwithstanding the low resolution.

Please step in here, video experts.


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As a non-scientific person, all I can comment is that I can tell the difference on my Panny 50" between the HD signal that comes in at 1080i and lower rez HD signal. It's quite obvious which stations are broadcasting an upconverted signal. CBS programs look sensational, while the few NBC HD broadcasts are inferior. Oddly enough, the PBS HD demo loop is gorgeous beyond belief, but The Ponder Heart looked upconverted to my eyes. I notice that some HBO/Showtime movies are broadcast in much better resolution that others. I've gotten so spoiled that I turn off the lower resolutions. Don't have much interest in any program not broadcast in HD.

I'm not completely certain how the Panny works as it supports both 1080i and 720p. The only time I can be certain that there is some scaling going on is during NYPD from ABC during which, sometimes, there is a slight delay in lip sync (easily rectified by my Integra Research RDC-7 preamp/surround processor).

Then to fully resolve HD shouldn't the native panel resolutions be 1920 x 540p (1080i samething?) or 1280 x 720p?

But a panel can't be optimised for both HD standards. Any ideas ??
nobody ever said the situation was optimized.

the point of scaling is to convert from an input resolution to a different, one assumes more appropriate, display resolution.

As far as image quality for up-scaled material, think of it this way:

if there are only 480 lines coming in, the nearest vertical spot of informtion is one of those lines away. if you scale that to 768 lines, the distance between those original spots is now 768/480 lines away, about a line and a half. You have more lines, but no more information to put on them, so the scaler invents more data and fills out the display. if the ratio was more like 1:2, the explantion would be easier...the scaler would be inventing 100% more data.

the pq problem is that the scaler's invented data is an approximation; that new data was never in the image and so might look fishy. Add moving images to the mix, then film and video sources with editing and cadence changes, etc. you can see why some scalers might be better than others and some material might scale better than other material.
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Then is the goal of a device like the native scaler which if available at the native resolution of a plasma panel, would be much better for sending interlaced NSTC video into the plasma display? This would then "bypass" the built in scaler as the video is already scaled to the progressive native rate of the display?

With the HD video, the internal scaler of the plasma will still process that video and scale it down if the video was originally 1280 x 720p and the native resolution of the plasma display is, say, 1024 x 768? Will the processing of the 1080i signal also be scaled "down" or scaled "up" into 1024 x 768 with that type of panel? Is it the vertical resolution of the panel and the video signal that is important here, ie 540p and 720p into a 1024 x 768 native resolution plasma display?

Thanks, Mark
that is the theory, mark. however, in practice there appear to be substantial challenges to getting a PDP to not "process" an input.

either (a) the "dot-by-dot" input is in PC mode with different (usually sub-optimal) settings for video (ie: it expects a PC screen, not a movie); or (b) the unit still keeps its electronics in-line if it's not in PC mode so you can only hope it's "not doing too much".

i too am interested in learnign more about this, so if i'm wrong, please won't somebody more educated beat me over the head!!!!


ADDENDUM: btw, this is why the Runco units are theoretically interesting. one assumes that they rip out all the internal NEC video processing electronics and what you're left with is a raw matrix of pixels that the companion outboard box can feed with data. so if you're gonna buy a PDP and an NR maybe you're better off buying a Runco PDP system. i dunno.
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I'm by no means and expert doody, but I am sure that trying to match up input resolutions (well lines, anyway) and pixels (vertical) is a waste of time.

I don't know of any plasmas that bypass the internal scaler in any circumstances. The video output from your satellite box (or whatever) is overscanned so that you don't get black lines on any edge of the screen. And so you need the h-pos, v-pos, h-size and v-size controls to make sure the picture is centred etc. These control are always in circuit and the plasma is always scaling.

So to try to get it all to "match up" pixel for pixel would be virtually impossible and probably yield no benefit.

Only when you have a 848x480 *digital* output, feeding a 848x480 panel *digitally*, via VDI or SDI, will this make any sense.

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Good question. What does happen to a high-resolution 1080i signal on a 1024X768 plasma panel? Say you're looking at a live U.S. Open tennis broadcast and CBS's HDTV court camera has zoomed in on Anna Kournikova's ear for a second as she serves.

According to CBS engineer Bob Ross (his 8/10 post here ), the camera isn't filtered and should deliver full-resolution 1/30-sec frames with 1920X1080 active pixels. In bright sunlight the camera might capture an ultra-fine blond hair, say, 1 or 2 pixels wide near Anna's ear.

Say that Kournikova blond hair signal (KBHS) makes it all the way to your HDTV receiver, despite MPEG-2 compression. Since there's little movement during that one-second shot, MPEG-2 isn't filtering high-resolution details such as the KBHS.

But the KBHS may not make it past the next step. According to the mid-1990s FCC's experts committee , whose report I simplified here (8/22 post; forum conversion scrambled chronology), your receiver's built-in filtering will whack some 20 percent off the horizontal resolution to minimize interlace artifacts.

So, the FCC's experts measured 800 X 1638 pixels for a stationary black-and-white test pattern. No doubt they used CRT displays with a 1080 horizontal-line raster. But their 1080 X 1920 test pattern, after filtering, only displayed 800 lines by 1638 pixels (see the 8/22 post above). A 1080-line CRT raster remains constant, but an interlaced video signal on such a raster usually delivers about 70% of its static vertical resolution to viewers because of the so-called Kell factor.

Say the KBHS makes it through, taking up two of the 1536 horizontal pixels per line involved (1920 - 20%). Next, circuits in the plasma panel combine all the pixels in the two 1/60-sec fields making up each 1/30-sec frame into a single 1/60-sec progressive frame.

Then the scaler has to squeeze this image into the plasma panel's 1024X768 pixels. Numerous algorithms can be used to manipulate the HDTV pixels, but the KBHS undoubtedly won't survive in its original form. Perhaps adjacent pixels would be blended that create the appearance of a single hair. Perhaps the KBHS would be filtered out.

Higher-grade CRTs can display the resolutions provided with 1080i signals after receiver filtering. High-end monitors can display an unfiltered full-resolution 1080i signal. Also, D-ILA systems use a hybrid progressive/interlace technique outlined here (my 9/17 post). Notice not everyone favors this hybrid technique. -- John
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many of these issues were hot a month or so ago; try a search for: "not-so native rate" in the processor forum. I too was anticipating the grail of "1:1 pixel mapping", but like chippy have decided that was a fruitless search (not necessarily a waste of time...I learned a bit).

The issue was provoked by the Faroudja, who used the 1280x768 Pioneer to demo its so-called "Native Rate" scaler, but could only get the system to work when they sent the pioneer the near-miss rate of 1280x720.

ericbee and I tested this business out with our pioneers and native rates and finally gave up. We couldn't get Faroudja to make a 1280x768 scaler, we found the pioneer had pre-set problems when it was fed its native rate of 1280x768 (from the vigatec) or 1366x768 from a Faroudja. And finally, we felt the display simply looked great with the near-miss of 1280x720.

so much for the grail.

there was one interesting response (i forget from whom) which blew off the importance of a digital image anyway, claiming that once the number of vertical lines was set, it didn't matter if there were a discrete number of image points in the signal or a continuous analog signal.
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