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Inconsistent Interlace Artifacts

post #1 of 6
4/9/09 at 5:12pm
Thread Starter 
I've got a Samsung 1368x760 LCD flat panel connected via HDMI to a DirecTV HD DVR.

What I have noticed is that the 720p content usually looks great. But the 1080i content varies from channel to channel. In particular, some channels have fantastic 1080i pictures that make me extremely happy I did not spend more money for a 1080p set. Others have pretty obvious interlace artifacts, clear stair stepping and discernible horizontal lines with a square-wave effect on the edges of objects.

What is the cause of this? Is it the way different broadcasters transmit their 1080i signal? Or is it DirecTV in they way they broadcast certain channels? Or is it the original source material? I would accuse the TV, except it handles some 1080i channels perfectly.
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post #2 of 6
4/9/09 at 5:28pm
Probably has to do with content that originates at 24p and undergoes 2:3 pulldown to get to 30i vs. content that is shot natively at 30i. The former can have the pulldown reversed to recover progressive frames (which should look great on a 768p set), while the latter needs to be deinterlaced, which can vary widely in quality from device to device. You might try setting your DVR to only output in 720p mode to determine if it has a better deinterlacer than the one in your set.
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post #3 of 6
4/10/09 at 7:56am
Mac,
Do you notice a difference between 1080i content filmed with SD cameras instead of HD resolution cameras?
I also suggest outputing 720p to your TV since any quality problems are much less in the TV up scaling from 720p to 1366x768 then they are in downscaling 1080i to 1366x768.
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post #4 of 6
4/11/09 at 3:30pm
Thread Starter 
Quote:
Originally Posted by walford View Post

Mac,
Do you notice a difference between 1080i content filmed with SD cameras instead of HD resolution cameras?
I also suggest outputing 720p to your TV since any quality problems are much less in the TV up scaling from 720p to 1366x768 then they are in downscaling 1080i to 1366x768.

Thanks guys. Switching my DVR output to 720p eliminated all of the interface artifacts. So I guess it's the TV (Samsung A450)? It is odd however, that it handles off-air 1080i broadcasts OK without any interlace artifacts. So perhaps it is something inherent to the DirectTV/DVR signal? I've heard DirecTV actually uses 1440, or even 1280, so perhaps that also results in a lower quality signal for the TV to process vs. off-air.

As to the SD cameras (4:3 720x480), yes those seem to show the most obvious artifacts over the HD (16:9).

I will note that there seems to be a subtle loss of quality between the 1080i and 720p downscaled content out of the DVR. Though I prefer that to the interlace artifacts. It seems to me that there is an actual loss of resolution by having the DVR output 1080x720. Since the TV is capable of 1366x768, It seems like downscaling 1920x1080 to the set's native resolution would result in more overall detail rather than downscaling to 1080x720 and then back up to 1366x768. Or, is that what the TV scaler is doing as well?
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post #5 of 6
4/11/09 at 6:20pm
720p is 1280x720p not 1080x720.
I don't think your TV is creaating any artifacts. I think your STB is.
Every scaling operation causes a loss of PQ. I reccomended 720p since you would have less PQ scaling loss with 720p broadcasts from a minor upscaling then you would have from much more significant scaling up scaling and downscaling of 720p broadcasts by sending them from your STB at 1080i.
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post #6 of 6
4/11/09 at 8:52pm
Quote:
Originally Posted by Mac128 View Post

Thanks guys. Switching my DVR output to 720p eliminated all of the interface artifacts. So I guess it's the TV (Samsung A450)? It is odd however, that it handles off-air 1080i broadcasts OK without any interlace artifacts. So perhaps it is something inherent to the DirectTV/DVR signal? I've heard DirecTV actually uses 1440, or even 1280, so perhaps that also results in a lower quality signal for the TV to process vs. off-air.

There's really not a in the way of 30i HD content on the broadcast nets beyond sports and late night shows like SNL and Leno. Most primetime shows are 24p pulled down to 30i, while two of the big three HD reality shows, Idol and Dancing with the Stars, air on 720p networks. The other big HD reality show, Survivor, is mostly 30p with only a few short segments of 30i. On the other hand, a good portion of the cheap HD shows on cable nets are done 30i. It's simply a matter of how the shows are shot, rather than any real difference between D* and OTA.

Quote:


I will note that there seems to be a subtle loss of quality between the 1080i and 720p downscaled content out of the DVR. Though I prefer that to the interlace artifacts. It seems to me that there is an actual loss of resolution by having the DVR output 1080x720. Since the TV is capable of 1366x768, It seems like downscaling 1920x1080 to the set's native resolution would result in more overall detail rather than downscaling to 1080x720 and then back up to 1366x768. Or, is that what the TV scaler is doing as well?

There will be always be some loss of quality when converting between 720p and 1080i. Native is often the best choice (if available), but if the TV doesn't handle interlaced content very well, then 720p is the superior choice.
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