Film-Tech Forum ARCHIVE: 720p to 1080i conversion for CRT-based displays

This is topic 720p to 1080i conversion for CRT-based displays in forum The Afterlife at Film-Tech Forum ARCHIVE.

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Posted by Evans A Criswell (Member # 381) on 03-13-2003, 03:18 PM:

Many HDTVs these days are capable of displaying 720p, but convert it to 1080i for display. My Sony 57" 16:9 set is one that does this.

Does anyone know the details of how most CRT-based HDTVs perform this conversion, and how "lossy" in terms of resolution lost or artifacts (motion, resampling) are introduced in the process? I've had a difficult time finding detailed information on this topic.

Posted by Brad Miller (Member # 2) on 03-13-2003, 03:20 PM:

Probably the best site for this is www.avscience.com Be forewarned though that the members there use LOTS of abbreviations in their posts and you may have to dedicate some time on the forums just figuring out what equipment some of their abbreviations are referring to. Other than that one beef, it's a very lively forum for home theater systems.

Posted by Mark Gulbrandsen (Member # 72) on 03-13-2003, 07:43 PM:

I have an original Mitsubishi DTV with seperate tuner. All conversion is done inside the tuiner itself and my set does switch between the two scanning frequencies, or what ever to display them. All of this goes over a big computer type cable to the TV set for data and system type. The video and sync pulses are via a seperate garden hose diameter RGBYVH cable, thats red, Green, Blue, Y, or luminance, Verticle, Horizontal (sync pulses). Deep in the TV's setup features accessed from the remote, are the adjustments for all the different formats for the different HDTV systems that it can decode. 720p looks considerably worse that 1080i does. The apparent resolution is about the same but there are alot more artifacts that can be seen....whilst 1080i is like watching a first generation Kodachrome 16mm film projected on a 50" screen!! Not nearly as many visible...and annoying......artifacts. Even my dog Miko loves to watch TV now......Animal Planets funniest pet videos is her favorite show!
we also now have 14 channels that are transmitting DTV signals here in SLC.

Mark

Posted by Evans A Criswell (Member # 381) on 03-14-2003, 02:09 PM:

Thanks for the link to that Home Theatre forum site, Brad. It looks like at some point I'll be going through that since I'm sure there's a ton of good information in there.

To summarize, it seems that the conversion is done using one of two methods:

1. Convert every other 720p (1280x720) frame to 1080p (1920x1080) by resampling (30 per second), then make 1080i frames out of the 1080p ones (straightforward, but it loses the information in every other 720p frame).

2. Convert every 720p frame to 1080p by resampling (60 per second), then construct 1080i images from each pair of 1080p frames by taking every other scan line from the first 1080p image and the remaining scan lines from the second 1080p image.

The second method probably has much smoother motion portrayal than the first. The first method is probably much easier and cheaper to implement.

Posted by Evans A Criswell (Member # 381) on 03-24-2003, 03:20 PM:

Guess this thread should be moved to afterlife?

Posted by Brad Miller (Member # 2) on 03-24-2003, 06:38 PM:

Just drop me an email whenever you see an old thread that belongs in one of the new forums please. [Smile]