Picking the right HDTV to purchase is difficult. An important consideration for a potential buyer is knowing how much resolution a particular HDTV extracts from a 1080i high definition signal. The HD Guru (Gary Merson), put 75 2007 HDTVs through a series of test signals to learn how different brands and models really perform. The specific results will appear in the November 2007 issue of Home Theater magazine (on newsstands around 10/7/07). Below is a synopsis of the findings.
All LCD flat panels, microdisplay rear projectors and most plasma HDTVs are progressive displays, meaning they (should) process all 1080 lines within a 1080i signal and display it at a set’s native resolution. (1080i is the broadcast standard for most HDTV networks including CBS, NBC, CW and HBO.) This is accomplished by deinterlacing the broadcast signal into progressive one. An HDTV that does not properly deinterlace the signal will only process a single field of 540 lines. Last year I tested 61 2006 models and discovered over half the sets failed to process all 1080 lines within the signal, reducing resolution up to fifty percent (depending on screenÃ¢â‚¬â„¢s native resolution). The 2007 sets fared better with slightly over 65 percent passing. This test was conducted using the Silicon Optix HQV HD test disc. (You can purchase this disc in the Blu-ray or HD DVD format, at a 25% discount at hdguru.com/?p=153).
Most scripted televisions programs and almost all movies are filmed 24 frames per second. For 1080i broadcasts, the 24 frames must be split into two fields. An HDTV’s ability to restore the split signals in the proper sequence by recombining the 1080i fields into 1080p frames is essential. Failure to do so can produce artifacts or a loss of resolution. This test is also on the Silicon Optix HD HQV test disc. The results of this test were disappointing with only 14 out of 75 sets (just 18.66%) properly handling the signal!
Can a 1080p HDTV resolve all horizontal detail down to a single pixel (out of 1920 pixels across)? To perform this test, I used a Sencore 403 HDTV signal generator with a pattern that has vertical alternating black and white lines, one pixel wide. If a set passes this test every vertical line should be clearly visible (as black and white). If there is some roll off in bandwidth, the lines appeared as dark gray and light gray and if the set was unable to resolve down to a single pixel the area of the screen would appear blank. Out of the twenty 1080p sets tested, 17 (85%) had full bandwidth, with the remainder exhibiting some signal roll off.
Static and Motion Resolution
A particular HDTV may resolve a stationary test signal at full bandwidth, but what happens when motion is introduced? The answer, the on-screen resolution drops. This can have a significant affect on your viewing experience, especially if you tastes tend toward sports and action. How much resolution loss occurs? To find out I used a new test tool called the FPD Benchmark Software for the Professional. This Blu-ray disc contains a pattern called a monoscope pattern (pictured above) which is made up of a series of four black lines drawn so they gradually come together in a wedge like pattern that appears at the top, bottom and sides. There are numbers adjacent to the lines indicating resolution. One section of the disc has the pattern stationary (static resolution), in the following section, the same Ã¢â‚¬Å“monoscopeÃ¢â‚¬Â pattern moves from left to right (motion resolution). The stationary number where all four lines could be distinguished was recorded and then the test was repeated with the motion pattern with the area where the four lines could still be discerned as separate and not blurred together was noted. These numbers were then compared.
The result, three distinct groups emerged from this test of the twenty 1080p displays. All displays in the top group were plasma HDTVs. They all had a static resolution of 1080 lines and a measured motion resolution of 830-880 lines, depending on the specific display. The next group consisted of microdisplay rear projectors, static measured 1050-1080 (depending on the display) while motion resolution ranged of 610-780 lines. The bottom group were all the LCD flat panels, with a static resolution of 400 (one panel) to 1080 lines and motion rez coming in at 360 lines (one set tested) to 600 lines. Three of the LCDs tested were 120 Hz models (one was the Sony KDL-46XBR4 reviewed here), all 120 Hz models had 600 lines of motion resolution.
The FPD test disc is currently not available to the public. However, the top industry HDTV reviewers have received copies of the disc and I expect this test to be included in reviews by others soon.
Copyright Ã‚Â©2007 Gary Merson/HD GuruÃ¢â€žÂ¢. All rights reserved. The content and photos within may not be distributed electronically or copied mechanically without specific written permission.