The simplest description of a scaler is "an electronic device that changes a signal from one
resolution into another resolution." All projectors, plasma screens, LCD screens and rear
projection displays have built in scalers. They must, since all displays accept multiple
types of video signals at various resolutions, yet only display one resolution. These types
of displays are known as "fixed resolution displays" because no matter what resolution signal
is sent to them, they can only display a finite fixed resolution known as the display's "native"
resolution. Video displays input multiple resolutions like SXGA, XGA, SVGA, NTSC and HDTV, and
convert those signals to the native resolution of the display. It might sound simple, but it's not.
Let's take a look at a few examples so we can get an idea of what is involved. Let's say we want
to take a picture of a circle that was recorded in XGA (1024 x 768) resolution and fed that image
to a display that has a native resolution of SVGA (800 x 600). The XGA image is originally
comprised of 786,432 individual pixels, but that number has to be reduced to 480,000 pixels.
That's a reduction of nearly 40%. The scaler uses a mathematical algorithm to best figure out
how to drop individual pixels, but still make the image look the same as the original.
If this is performed well, it should look like this:
A perfect circle, but smaller in size than the original. But if the scaler isn't of a high caliber,
it could turn out like this:
Notice that the edges aren't quite what they should be. They are uneven and rough in appearance.
Now imagine a much more complex object, like humans, or moving scenery. Scaling complex images
can be much harder and more important to be done with precision.
The scaler's hardest task is to scale down an image like we just described, such as scaling down
a 720p HDTV image to display on a 854 x 480 resolution display. In that scenario, the scaler is
throwing away 55.5% of the available information. Loss of detail is inevitable. To combat this,
out advice is to try to choose a display device that best matches the resolution of the majority
of the source material you'll be watching.
It is much harder to take away information from the original image — and still make it look like
an exact copy of the original image — than it is to add information to that original image
(blow it up in size) and still have it look like the original.
The scaling of an image is the last step of image processing that is done to actually create
the image on your screen. For the best image possible, look for name brand scalers that are
incorporated into your display device such as PixelWorks and Faroudja.
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