Are You Getting All the Resolution You are Paying For? More Tests
In the November 2006 issue of Home Theater Magazine the HD Guru tested 61 new HDTVs using the 1080i HDTV format that most of the HDTV channels use (including CBS, NBC, CW, MTV HD, and Wealth HD), as well as the current HD DVD and Blu-ray disc players. The question was, does the latest crop of HDTVs retain all of the detail in the broadcast or HD disc and send it to the screens at its native resolution? Or do they fail to properly handle the signal, cutting the image resolution down by as much as 50 percent?
The 1080i SMPTE 133 test pattern from the disc contains an image. In the corners and to the right of the middle of the image are boxes with alternating horizontal black and white lines a single pixel high. (See the illustration at the website listed at the end – note: some detail was lost shrinking the image to fit the web) The TV sends the white lines (odd numbered) to the first field, and the second field contains the black lines (even numbered). To add a motion component (proper deinterlace of still frames doesn’t count since we are dealing with “motion” pictures, not a slide show), a clockwise rotating white line is positioned on the left side of the pattern. If a given display properly processes all of the lines, the pattern’s alternating horizontal lines should remain intact. If the display only shows single 540-line fields (all odd- or all even-numbered lines) and up converts to the TV’s native resolution, the boxes will strobe all black and then all white. If this occurs at any time, I give the display a “fail,” because the display only works with half of the available information as it strobes.
Many scripted television and all film-based movies that telecast in 1080i HD are recorded at 24 frames per second. For broadcast, this is converted from film or 1080p/24 video to 1080i/30 using a telexing conversion. A good internal processor should use a method called HD inverse telexing to recognize like frames and reconstruct them for a 60-frame-per-second display using a 3:2 cadence. If the processor reconstructs the image properly, you’ll see all 2-million-plus pixels of information in the original source material (on a 1080p display). A 720p display will down convert the full 1,920-by-1, 080 images to 1,280 by 720. Without HD inverse telexing, the television’s processor may discard up to half of the image resolution (prior to conversion in 720p displays) during horizontal pans. So, regardless of what you may have read elsewhere-or what your local TV-store sales clerk has told you-if a 1080p display’s processor is capable of content based on HD 3:2 inverse telexing (and properly deinterlace, as well), you can see all of the content in full 1080p resolution. You don’t need to wait for 1080p broadcast or HD DVD disc players with 1080p output to do so. This test also uses the SMPTE 133 pattern (without the addition of the rotating white line) panned right to left and back again at 24 frames per second. The Silicon Optix 1080i HQV HD DVD is mastered at 1080i/30 with a 3:2 cadence inserted, like any 24-frame film transfer to video. If the processor properly handles the signal, the boxes with the horizontal lines described above will remain intact. If not, either the boxes will strobe between all black and all white (as with the deinterlace test), or you will see vertical bands on the sides of the box. (See image directly below) Stroking or banding constitutes a “fail,” as resolution will drop during motion.
I performed this test on the 1080p displays. The SMPTE 133 pattern has boxes with alternating black and white vertical lines. The lines in five of the boxes in the test signal are one pixel wide, representing the finest detail in a 1080i signal. If the display passes the full bandwidth, you’ll see vertical black and white stripes. If there is an attenuation of the signal-which may translate into a loss of some fine detail in actual content-the lines will appear as dark gray alternating with light gray. If you can’t see any lines, the display is not passing any fine detail to the screen. This means that a display can be native 1080p, with 1,920 pixels across, but no detail that is one pixel wide will make it to the screen. I’ve noted the sets that showed some signal attenuation with “some.”
The 14 2006 models came from eight vendors and include new brands such as Visio and Olivia. All results are based on factory default settings. Please note the new Sharp 62 series models tested omit a menu button on the television. These were in-store tests. The major retailers no longer provide remote controls on the sales floor, preventing an opportunity for the HD Guru or anyone else from changing the picture settings from factory default.First up was the deinterlace test. The bad news, only 7 of the 14, 50% latest 2006 models passed the test a fraction of a percent less than passed the tests of the 61 2006 models. The good news is all the Mitsubishi and the Vizio plasma passed this tests. The 3:2 test were a disaster, with only 14.28% of the 14 (2 of 14) sets tested passed. With 85.72% failing this is higher percentage than the 80.33% fail rate of the last go around. . The two passing models were the Vizio plasma and one Sony LCD flat panel. See the previous tests for more Sony results. The 1080 bandwidth test applies only to the seven models with 1080p resolution. I would have preferred to see some of the sets pass single pixel on/off test pattern without attenuation, but Ã¢â‚¬Å“some Ã¢â‚¬Â is better than none of the test signal. While good signal processing for proper deinterlacing, 3:2 conversion, and bandwidth is extremely important to obtain a superb high-definition picture, there are some other factors-including contrast ratio, motion lag, and black level-that make big differences in picture quality. Use the chart to find the sets that pass, and then compare the passing sets with other displays. If the other factors are about the same, the HDTV with the proper signal processing will produce the better image.
768p= the 768 line resolution
Parts of this article are reprinted with permission of Home Theater magazine. For the complete version including earlier test results of 61 displays go to http://www.hometheatermag.com/hookmeup/1106hook/index.html
|Olevia||227V 27″||LCD||Fail||Fail||NA 720p|
|Samsung||4676S 46″||DLP||Fail||Fail||NA 720p|
|Sony||KDL32S2010 32″||LCD||Fail||Pass||NA 768p|
|Sylvania||6637LCT 37″||LCD||Fail||Fail||NA 768p|
|Sylvania||842THG 42″||Plasma||Fail||Fail||NA 768p|
|Visio||P50HDTV10A 50″||Plasma||Pass||Pass||NA 768p|