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Discussion Starter · #1 ·
Could someone kindly give me a better understanding of what a scaler does? There seems to be some confusion about this (on my part for sure, but also others), an assumption perhaps that a scaler is a line-doubler or de-interlacer, but I take it to be something different. I'm thinking about getting an iScan for 480i-480p conversion, but I understand it does not function as a scaler. Help please.
 

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What people refer to as a "scaler" is typically a deinterlacer and scaler in one box. In order to scale an image properly, it must be progressive, so a deinterlacer is required to scale an interlaced image. Even if the input is interlaced (like 480i) and the output is interlaced (like 1080i) internally the signal must be converted to progressive to do the scaling.


Since the deinterlacer is basically implied, people refer to these boxes as "scalers" and not generally "deinterlacer/scalers."


An iScan is not a scaler, but is just a deinterlacer. It takes 480i in and outputs 480p. Some call deinterlacers "line doublers" but that's a misleading term that I don't like to use. The number of vertical lines visible on screen is not being doubled. A 480-line interlaced image is just being converted to a 480-line progressive image. This does double the total number of lines being sent to the display, because the 480 lines are being drawn twice as fast, but visually the result is not equivalent to doubling the displayed resolution.


Does that help?


Don
 

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You might also want to start reading the "Video Processors" section of AVS Forum, which is where they discuss deinterlacers and scalers.


Don
 

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Discussion Starter · #5 ·
Seems I'm often wandering around in the wrong forum. Thanks, Don, for spotting me in the these thickets inhabited by Denons and a Sonic Pan and steering me in the right direction. That was Food Processors, right? Must be scalers are people watching their weight. (I'd put a winking smiley here but I'm too old for that sort of thing). Cheers
 

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Scaling is changing the nominal resolution of an image. For example, changing a 640x480 image to a 1024x768 image would be a scaling operation. Because there are more pixels in the 1024x768 image, the scaler must interpolate the new pixels by mathematically averaging the nearby pixels in the original image (roughly speaking). Going the other way, from 1024x768 to 640x480 for example, requires the scaler to selectively remove information by lowpass filtering the spacial frequencies and then resampling the image at the new resolution.


It's important to note that scaling can't create real information. Even when a scaler makes the nominal resolution higher, there is still only as much information in the image as the original pixels could represent. So a 720x480 image scaled up to 1280x720 will never look as good as an image that was created at 1280x720 in the first place from a camera or scanner.


Beyond that, I think you'd better just hit Google and start reading. :)


Best,

Don
 

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Discussion Starter · #7 ·
Don, I edited just after your response. Looks like the "right" forum has the answers I'm looking for. As with a few others who've been helpful to me (Rich Harkness, MrGonk, Adu, others), I'm sometimes amazed at the patience and willingness to help I encounter here. Thanks.
 
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