How upscaling works

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With the advent of high definition television, the development of components to match the resolution capabilities of HDTV are becoming more important. As a solution, more and more DVD players are equipped with "upscaling" capability to better match the performance of the DVD player with the capabilities of the today's HDTV's.
However, the introduction of Blu-ray and HD-DVD has confused the issue regarding the difference between the upscaling of standard DVD and the true high definition capability of Blu-ray.
Standard DVD Resolution
A standard DVD player, without upscaling, can output video resolution at 720x480 (480i). A progressive scan DVD player, without upscaling, can output 720x480 (480p - progressive scan) video signals.
480i represents 720 pixels displayed across a screen horizontally and 480 pixels down a screen vertically. This arrangement yields 480 horizontal lines, which are, in turn, displayed alternately. In other words, all the odd lines are displayed, followed by all the even lines.
480p represents 720 pixels displayed across the screen horizontally and 480 pixels down the screen vertically. This arrangement yields 480 horizontal lines on the screen, which are, in turn, displayed progressively, or each line displayed following another.
The Upscaling Process
Upscaling is a process that mathematically matches the pixel count of the output of the DVD signal to the physical pixel count on an HDTV, which is typically 1280x720 (720p) or 1920x1080 (1080i - and, some cases, 1080p).
720p represents 1,280 pixels displayed across the screen horizontally and 720 pixels down the screen vertically. This arrangement yields 720 horizontal lines on the screen, which are, in turn, displayed progressively, or each line displayed following another.
1080i represents 1,920 pixels displayed across a screen horizontally and 1,080 pixels down a screen vertically. This arrangement yields 1,080 horizontal lines, which are, in turn, displayed alternately. In other words, all the odd lines are displayed, followed by all the even lines.
1080p, on the other hand, represents 1,080 horizontal lines displayed sequentially. This means all lines are displayed during the same pass. 1080p is the highest quality HD display format.
The Practical Effect Of DVD Upscaling
Visually, there is very little difference to the eye of the average consumer between 720p and 1080i. However, 720p can deliver a slightly smoother-looking image, due to the fact that lines and pixels are displayed in a consecutive pattern, rather than in an alternate pattern.
The upscaling process does a good job of matching the upscaled pixel output of a DVD player to the native pixel display resolution of an HDTV capable television, resulting in better detail and color consistency.
However, upscaling, as it is currently implemented, cannot convert standard DVD images into true high-definition images. In fact, although upscaling works well with fixed pixel displays, such as Plasma and LCD televisions, results are not always consistent on CRT-based high definition televisions.