2.35:1 And HD Resolution
Dear Gary: Great job with Widescreen Review—it’s the best magazine out there. I look forward to it every month. Please help clear up confusion I’m having regarding HD movie aspect ratios’ impact on resolution. Specifically, I own Pioneer’s Elite 610 and JVC’s new HM-DH30000U HD VCR. As you know, the shape of the screen on the 610 is 1.85:1, as is the standard for HD. What is the impact on HD’s 1080i resolution when the aspect ratio of the movie is different than 1.85:1? For example, if the aspect ratio is 2.35:1, e.g., Terminator 2: Judgment Day, a narrower picture, are some resolution lines wasted with the black bars above and below the picture? If so, can there ever be true HD with films that have an aspect ratio other than 1.85:1?
Bruce Dimler
Video Technical Editor Greg Rogers Comments:
Although I haven’t measured the screen dimensions of the Pioneer Elite Pro-610HD, I believe it has a 16:9 (1.78:1) display in accordance with HDTV standards, rather than 1.85:1. This is a minor difference and in many cases movies with a 1.85:1 aspect ratio will be cropped by 2 percent on each side to create a 1.78:1 picture when transferring the movie from film to HDTV video. An alternative is to letterbox the 1.85:1 image within the 1.78:1 HDTV frame with very small (2 percent of the height) black bars at the top and bottom of the frame. These bars won’t normally be visible on a rear projection display because picture overscan is usually set at 3 to 5 percent on each edge, but the difference is noticeable on most front projection systems. Whenever the complete image of a film with an aspect ratio wider than 1.78:1 is transferred to HDTV, the image must be letterboxed. A 2.35:1 image will occupy only 76 percent of the 1.78:1 frame height, with black bars filling the remaining area above and below the film image. In that sense, 24 percent of the scan lines (or pixels) are “wasted” in the black bars. But the great advantage of HDTV is that 819 scan lines still remain in a 1080i frame to represent a 2.35:1 image, compared to only 365 scan lines in a 1.78:1 format DVD frame for the same image. You ask if this is “true HD?” The pixel resolution of the 2.35:1 image is 1920 x 819, which is more than 1.5 million pixels. So by just about anyone’s measure, this is still high-definition TV. Of course another alternative is to crop the sides of a 2.35:1 film to fit a 1.78:1 screen. Several broadcasters are doing this to avoid black letterbox bars, rather than to preserve resolution. But this throws away 24 percent of the film image and is unacceptable to most of us movie enthusiasts.
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