If you bought a gallon of milk and found it half-empty, it’s a safe bet you’d raise heck with the store manager. Similarly, if you bought tickets to a basketball game that ended at halftime, you’d want a refund. So why settle for half the picture resolution on your HD monitor or projector?
There’s a lot of pixel information in each frame of a 1920x1080 image - over 2 million pixels, to be exact – and it stands to reason that display and interface manufacturers would bring to bear a commensurate amount of de-interlacing and adaptive motion correction before those images appear on your screen.
Guess what? It doesn’t. You’re getting cheated.
The average HDTV monitor, TV, or projector is taking the fast and easy way out by grabbing one of the two available interlaced image fields and performing all of the processing on that field. That means you wind up seeing just 540 of the available 1080i scan lines.
Now, the result isn’t so bad when viewed on a smaller CRT monitor or TV, where the resolution of the scanning CRT isn’t sufficient to show much more than 600 lines to begin with. And a display with 720p or 768p native resolution still masks this loss of image detail to a lesser degree.
However, when you view 1080i programs on a true 1920x1080 display, things begin to fall apart. At the recent Home Entertainment Show, Silicon Optix had a demo of their Realta HQV 1080i processing, using a JVC DLA-HD2K (1920x1080 LCOS) front projector.
Displaying several clips of live 1080i footage, they showed the difference between their intensive frame-based de-interlacing and the more common field-based de-interlacing used by probably 99 percent of the projector and monitor manufacturers, and even some name-brand video scalers. With the field-based process, there was a subtle but noticeable loss of detail evident in freeze frames, and plenty of residual scan line artifacts were observed across people’s faces, signs, and solid objects.
Some of us have known about this dirty little secret for some time. Remember RCA’s first satellite/broadcast DTV receiver, the DTC100? Using field-based deinterlacing, it converted 1080i signals to 540p to drive its companion TV set. Processing both field of a 1080i signal takes a lot of horsepower, but 540 lines? Heck, that’s child’s play.
With professional and consumer display markets starting to adopt true 1080p imaging, it’s becoming evident that field-based processing of 1080i just won’t cut it. And MPEG compression artifacts such as macroblocking and mosquito noise will only make matters worse.
As we sit around and debate the relative merits of the 720p vs. 1080i HD formats, one thing the 720p proponents can use as leverage is this emasculation of 1080i image quality at the display level. While Silicon Optix is hard at work on a solution, it remains to be seen how other manufacturers of 1080p displays will respond – or if they even realize there is a problem.
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