Maybe yet another victim of a somewhat less than honest sales pitch?Are You Getting All the HDTV Resolution You Expected?
Gary Merson, May, 2006
Which displays have it and which don't.
The current top HDTV broadcast resolution is 1080i (interlaced). Most television and cable networks use it, including CBS, NBC, the WB, HBO, Showtime, HDNet, The Movie Channel, Starz HDTV, and others. What happens to this HDTV signal when one of the latest digital HDTVs processes it? Does it take the full 1,080 lines of transmitted resolution, change the signal from interlaced to progressive (called deinterlacing), detect and compensate for motion, and send it to the screen, as it should? Or does the display's processor cheat you out of seeing all the detail within the broadcast?
I tested 54 of the 2005 model year's high-definition digital displays, including some of the latest 1080p TVs, to determine which manufacturers' internal scalers process all 1,080 lines and which do not. More than 48 percent of the displays I tested failed to process and deinterlace the 1080i signal properly, losing up to one-half of the vertical resolution. How is this possible?
A number of TV vendors opt to use a simpler and cheaper way to process 1080i signals. They do it by handling one 540-line field at a time and upconverting the one-half-resolution picture to the given digital HD set's native resolution. To get a sense of how askew this is, note that HD displays have 720, 768, or, in the case of the highest-resolution HDTVs, 1,080 horizontal lines.
Why Does This Occur?
Almost all digital displays are progressive, whether they be flat-panel (LCD, plasma) or microdisplay front- or rear-projection (DLP, LCD, and LCOS-also known as D-ILA and SXRD by certain manufacturers). This means that, every 1/60 of a second, they create a complete image in which all lines of resolution appear on the screen at once. With a 1080i broadcast signal, a full 1,080-line image frame is broken into two halves, and each is sent to your display in an alternating fashion. The first half contains 540 odd-numbered lines (called a field) of resolution (lines 1,3,5, etc.). This field is sent during the first 1/60 of a second. The second field is sent during the next 1/60 of a second. It contains the even-numbered lines (lines 2,4,6, etc.; see illustrations). The process repeats itself over and over. To get all 1,080 interlaced lines to appear on the screen at the same time on a progressive high-definition display, the processor within the HD set has to weave together both 540-line segments to form the full-resolution frame (like the image below).
It does so by holding the first field in its memory, receiving the next field, then electronically knitting the two fields together. These processors should also compensate for motion within the image by detecting the specific moving areas of the image. A good-quality processor should also incorporate advanced filtering to prevent digital artifacts such as jaggies. (For more info on this, check our November and December 2005 issues or here and here.)
Cheap, unsophisticated signal processors simply take a single 540-line field and synthesize all the missing lines of information to create the number of lines of the display, which can be 720, 768, or 1,080, depending on the display's native resolution. This method of scaling results in a softer picture accompanied by motion artifacts. Seeing as little as half of a display's full resolution is not all that desirable. This method is sometimes referred to as bobbing (Illustrated in the image below).
That four consumer electronics companies (JVC, Hitachi, Pioneer, and Toshiba) have been boasting for the last couple of years that their displays properly process all the 1,080 broadcast lines at once should help further illustrate the importance of proper signal processing of 1080i broadcasts. According to our tests, these displays really do.
I conducted the testing by connecting a PC with a MyHD video card to each display. The test pattern I used to determine how the processor functions is called SMPTE 133. The pattern is a 1080i file that was output from the video card's component video output, set at 1080i. This image has five boxes with alternating horizontal black and white lines, each occupying a single scan line. A white line that rotates 360 degrees is overlaid on the pattern, to simulate motion. Displays that properly deinterlace and pass this test continue to show the boxes with the horizontal black and white lines. The ones that fail flicker instead, making the boxes switch from white to black to white continuously. This is because they double the first field that
A number of factors determine how sharp and clear an HD display appears. Among them are bandwidth, contrast ratio, black level, and optics (in projectors). Good signal processing is very important, and, all things being equal, a display that properly deinterlaces and processes 1080i will yield a better picture than one that doesn't. Check our chart to determine if the displays you are considering pass or fail.
Make/Model Technology Native Resolution Pass/Fail
Audiovox FP-3705 LCD FP 768p Fail
Epson LS65HD1 3LCD RP 1080p Pass
Hitachi 60VX915 3LCD RP 720p Pass
JVC LT32X576 LCD FP 768p Pass
JVC LT-40X776 LCD FP 768p Pass
JVC HD526886 LCOS RP 720p Pass
LG DU37LZ30 LCD FP 768p Fail
LG DU42PX12X Plasma FP 768p Fail
Mitsubishi WD-62627 DLP RP 1080p Fail
Mitsubishi WD-73927 DLP RP 1080p Fail
Mitsubishi WD-52627 DLP RP 1080p Fail
Mitsubishi WD-52527 3LCD RP 720p Fail
Mitsubishi LC-3780 LCD FP 1080p Pass
Mitsubishi PD-4265 Plasma FP 768p Pass
Mitsubishi PD-5050 Plasma FP 768p Pass
Panasonic PJ44LCX65 3LCD RP 720p Fail
Panasonic PJ52LCX65 3LCD RP 720p Fail
Panasonic TH-37PX50 Plasma 768p Pass
Panasonic TH-50PX50 Plasma 768p Pass
Philips 37PF7320A LCD FP 768p Fail
Philips 32PF7320 LCD FP 768p Fail
Philips 26PF5320 LCD FP 768p Pass
Philips 37PF7320 LCD FP 768p Fail
Philips 427230A Plasma 768p Fail
Philips 429630A Plasma 768p Fail
Philips 50PF9630A Plasma FP 768p Fail
Pioneer Pro 930 Plasma FP 768p Pass
RCA HD50LPW164 DLP RP 720p Fail
RCA HD50LPW175 DLP RP 720p Fail
Samsung HL-R5668 DLP RP 1080p Pass
Samsung HL-R5067 DLP RP 720p Fail
Samsung HL-R5667 DLP RP 720p Fail
Samsung HL-R6167 DLP RP 720p Fail
Samsung HL-R4667 DLP RP 720p Fail
Samsung LNR408D LCD FP 768P Pass
Samsung LNR268W LCD FP 768p Pass
Samsung HPR-5052 Plasma FP 768p Pass
Samsung HPR-4252 Plasma FP 768p Pass
Sharp LC-45GD5U LCD FP 1080p Fail
Sharp LC-32GB5U LCD FP 768p Fail
Sharp LC-32D5U LCD FP 768p Fail
Sony KDF-55A20 LCD RP 768p Fail
Sony KDSR60XBR1 LCOS RP 1080p Pass
Sony KDSR50XBR1 LCOS RP 1080p Pass
Sony KDFE-42A10 3LCD RP 720p Pass
Sony KDFE-50A10 3LCD RP 720p Pass
Sony KLVS32A10 LCD FP 768p Fail
Sony KLV32XBR1 LCD FP 768p Pass
Sony KDL26XBR1 LCD FP 768p Pass
Toshiba 46HM95 DLP RP 720p Pass
Toshiba 52HM95 DLP RP 720p Pass
Toshiba 37HL95 LCD FP 768p Pass
Westinghouse LVM-37W1 LCD FP 1080p Pass
Yamaha DPX-1300 DLP FP 720p Pass
Total Sets: 54
Passed: 28
Fail: 26
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