HDTV Resolution and Pixel Count?

Q. Regarding Alan Lofft's column entitled ““Standard or High Definition: It's All in the Pixel Count,”” if I have a Samsung DLP HDTV that has a native resolution of 1280 x 720p and I'm watching HDNet, which uses a 1080i signal, there is no way I'm going to get the number of pixels that come with that 1920 x 1080i format . . . right? The native resolution on a set is the maximum number of pixels that can possibly be displayed? Also, do the 720p and 1080i figures refer to the horizontal or vertical number lines? Thanks for answering my questions on pixel count. - Patrick

A. The 720p and 1080i figures refer to the number of horizontal lines stacked vertically from top to bottom of the screen. Those are also called ““vertical resolution.”” The 1280 and 1920 figures (called ““horizontal resolution””) are the total number of individual pixels (picture elements) across each of the horizontal lines for the 720p and 1080i formats, respectively. So it's true that in your example you won't get all 1920 pixels of HDNet's horizontal resolution from your Samsung's 1280 x 720p display. The Samsung DLP, a plasma, or an LCD panel are all "fixed-pixel arrays,”” and the Samsung's micro-mirror DLP chip has a native resolution of 1280 x 720p. Likewise, a plasma or LCD flat-panel will have a fixed number of pixels across each of its horizontal lines which may or may not exactly correspond with the transmission standard, just as the 1920 pixels that HDNet uses aren't an exact fit for the 1280 pixels of the Samsung DLP chip. But that doesn't matter because the Samsung or plasma set's internal digital scaler will automatically convert all incoming video to ““fit”” its native resolution. And in my experience the differences, if at all visible, are very tiny. The really visible differences occur at a pixel count between 480p and 720p, or between 480i and 1080i, the differences between Standard Definition and High Definition.

TV Resolutions

Moreover, the overall clarity of a DVD displayed on an HD set is affected by the original movie or program's aspect ratio, which may not be identical to the 16:9 (1:85:1) widescreen standard adopted for HD. If you watch some extremely widescreen movies such as ““Lawrence of Arabia”” (2:35:1), not all the pixels are used by the scanner during the digital transfer to DVD. Consequently, when you watch playback on your HD widescreen set, there will be black bars at the top and bottom of the image, even on a 16 x 9 display. This lessens overall resolution, because all the pixels used to display the black bars are not used for image display. Fewer pixels used for picture content equals lessened resolution. It's visible, but in my opinion this variation in pixel count is not a big deal.

Now that you know all about pixel count, check out my tips on tweaking your tv!

Alan Lofft

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