# AskDBStalk: 480p down conversion



## paulcdavis (Jan 22, 2004)

When the 921 down converts 1080i or 720p to 480p, the number of horizontal lines is reduced, but what happens to the number of pixels in a line? Is it 480 as in OTA SD, or 720 like a DVD, or 1024 as in 720p or 1920 as in 1080i or some other number or varies with the source?


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## Mark Lamutt (Mar 24, 2002)

I have no idea, and don't have a good idea how to determine. Anyone else?


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## Mike123abc (Jul 19, 2002)

You would need the line count test pattern (I do not know its official name). It has a series of lines closer and closer together and finer and finer. They are labeled and you see where your TV/signal loses resolution. Does HDNET broadcast them in their test pattern show? I have never watched it.


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## Mike123abc (Jul 19, 2002)

To me it personally looks like 704 or 720, I use 480p all the time except when I want to seriously watch HD then I switch it to 1080i.


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## Richard Chalk (Jan 4, 2004)

paulcdavis said:


> When the 921 down converts 1080i or 720p to 480p, the number of horizontal lines is reduced, but what happens to the number of pixels in a line? Is it 480 as in OTA SD, or 720 like a DVD, or 1024 as in 720p or 1920 as in 1080i or some other number or varies with the source?


If the image starts out 16:9, and is down-converted by sampling, then the horizontal resolution has to decrease by the same proportion. Otherwise, the image will no longer be 16:9.
The same would be true of 4:3 images.

Remember the computer 4:3 ratios of 640 x 480, 800 x 600, 1024 x 768, etc.

For 16:9, they are 853 x 480, 1280 x 720, and 1920 x 1080.

These are the absolute values, but there are almost no TV displays that can actually show 1920 horizontal pixels. A typical projection TV with 7" CRTs is limited to about 1200, due to the spot size required to get sufficient brightness.

Richard

Richard


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## paulcdavis (Jan 22, 2004)

Thanks for the suggestions. I have a timer set to record the HDnet test pattern on Tuesday, so I'll try to see if I can get a readingfor resolution at both 480p and 1080i and report back.


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