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HR20 Video Scaler


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10 replies to this topic

#1 OFFLINE   ericlhyman

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Posted 11 May 2007 - 01:09 PM

What video scaler chip does the HR20 use and how well does it handle scaling compared to sending out the native signal and letting a recent Sony HDTV do the scaling?

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#2 OFFLINE   davring

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Posted 11 May 2007 - 01:17 PM

What video scaler chip does the HR20 use and how well does it handle scaling compared to sending out the native signal and letting a recent Sony HDTV do the scaling?



I'm not certain what chip it uses but I think it does a good job as I really can't see much difference between the TV and the HR20 functions. I think my Sony does a tad bit better. Considering what I paid for the set it makes me feel better to think it does anyway...:lol:
HR20-700(2.0TB)>Sony XBR-55HX929
HR20-700>Sony KDL40V2500
OTA RS outdoor ant
Hardwire networked to Cysco Router 6.0 AT&T DSL
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R15-500>Samsung LNT2342H
DirecTV customer since 1997

#3 OFFLINE   techntrek

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Posted 11 May 2007 - 01:27 PM

Theoretically the DVR would do a better job since it has access to more behind-the-scenes info as its decompressing the MPEG signal.

#4 OFFLINE   rminsk

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Posted 11 May 2007 - 03:28 PM

Theoretically the DVR would do a better job since it has access to more behind-the-scenes info as its decompressing the MPEG signal.

If you are feeding a digital signal to the TV the TV has the exact same information that the HR20 has at the time the scaling is done.

#5 OFFLINE   veryoldschool

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Posted 11 May 2007 - 03:35 PM

If you are feeding a digital signal to the TV the TV has the exact same information that the HR20 has at the time the scaling is done.

I think this is true for MPEG-2, but not for de-interlacing, where there is more data available to the HR-20 than is sent over the HDMI
A.K.A VOS

#6 OFFLINE   rminsk

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Posted 11 May 2007 - 05:34 PM

I think this is true for MPEG-2, but not for de-interlacing, where there is more data available to the HR-20 than is sent over the HDMI

You do not need any extra information to deinterlace a 60i image.

#7 OFFLINE   veryoldschool

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Posted 11 May 2007 - 05:44 PM

You do not need any extra information to deinterlace a 60i image.

This is not my "field" but from someone that does seem to know: there is motion vectoring data that the HR-20 receives that can improve "i or p" convertion, that isn't sent through the HDMI.
I will stop now & let those that know more on the topic debate this.
I've kicked it enough to know there was some truth to what they posted about it.
A.K.A VOS

#8 OFFLINE   skaeight

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Posted 12 May 2007 - 07:12 AM

Anyone else have any thoughts on this? I just did a quick comparison of native 480i vs upconverted 480p, 720p and 1080i, and honestly saw no difference. I think I'm going to continue to run the HR20 in native mode. I like the idea of seeing things in their orignal format (especially HD).

I ended up buying an Aquos, which as far as I know has a pretty good upscaller, so maybe that's why I don't see a difference. I was originally looking at Vizios which have lousy upscallers, so I wasn't planning on using native mode if I had bought one of those.

#9 OFFLINE   veryoldschool

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Posted 12 May 2007 - 08:20 AM

Anyone else have any thoughts on this? I just did a quick comparison of native 480i vs upconverted 480p, 720p and 1080i, and honestly saw no difference. I think I'm going to continue to run the HR20 in native mode. I like the idea of seeing things in their orignal format (especially HD).

I ended up buying an Aquos, which as far as I know has a pretty good upscaller, so maybe that's why I don't see a difference. I was originally looking at Vizios which have lousy upscallers, so I wasn't planning on using native mode if I had bought one of those.

The whole using native on or off thing has been & will be debated for...well forever.
Here is some more on it: http://www.dbstalk.c...ead.php?t=81801
A.K.A VOS

#10 OFFLINE   Diana C

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Posted 12 May 2007 - 08:35 AM

We've had this discussion a bunch of times already, and after the last one, I did some research. Here is what I have found so far...

If we are talking about film original material delivered in 1080ix60 then, theoretically, there is information in the MPEG data that can aid in the deinterlace process. This is because most such content is really 1080px30 tagged at 1080ix60. Video original content is actual 1080ix60. The result of this is that each field in a video source is taken 1/60 of a second after the previous one. But in film original material every other field is taken at the same moment as the previous field and the pair are 1/30 of a second later than the previous pair.

NOTE: This is somewhat simplified...3:2 pulldown complicates this analysis since the 1/30 of a second field groups really come in groups of 3 and 2, since the film is really 24 frames per second, not 30. Reversing this process, called "reverse telecine" is another factor, but VERY few TVs do it correctly, and the HR20 is unlikely to do it correctly either.

This has an influence on how the fields are de-interlaced back into a single frame of prograssive scan data. If the scan convertor has access to the "true" encoding information it can handle each differently, and correctly. If not, it must rely upon some sophisticated analysis of the video field to determine what is moving, and how that movement is represented in the data. In MPEG4, this movement data is provided as part of the vector analysis done as part of the compression process.

However, since all MPEG data we get via DirecTV has been re-encoded by DirecTV from MPEG2 sources, it is unclear how much of this information, even if available, is accurate. Further, even if it is available and accurate, it is unknown whether or not the HR20 decoders are capable of feeding it to the scan convertor.

The only way to be sure is to run a series of tests with a TV known to NOT do reverse telecine and scan conversions correctly, and then feed a test signal through the HR20 to see if the problems are corrected by the HR20. This is obviously not something that can be done unless DirecTV broadcasts such a test. The HDNet test pattern can only test resolution conversion, it can't test the other points since there is no movement to speak of.

#11 OFFLINE   techntrek

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Posted 14 May 2007 - 06:24 AM

Titan25 basically says what I was getting at. There is a lot of guesswork/prediction encoded into both 2 and 4, much more in MPEG-4. With MPEG-4 this includes things like dropping chroma info from many frames, expanding its prediction routine to look many more frames ahead, and dividing the screen up into a smaller grid (MPEG applies its routines to each part of a grid, not the whole screen at once). Thus the additional compression achieved over MPEG-2.

The TV does not have access to any of this info. Once you send the signal via HDMI or component, you are getting a raw video feed and not the compressed file format. All of the prediction has been done and any upscaling/downscaling that your TV does is guesswork on top of guesswork. Now if your TV has its own OTA tuner (fed direcly with coax from an antenna), whether the TV's own decoding of the MPEG-2 stream is any better than the HR-20's will definitely be different from model to model, and from one software version (both the TV's and the HR-20's) to the next. But for the MPEG-4 streams coming from the sat, the HR-20 just has more info to work with from the start and can target the decompression for the resolution you have selected. Theoretically. I'm a programmer, but not for DirecTV or for video processors, so in reality the HR-20 may be much more loose in how it processes its sat signal.

Its kind of like a JPEG picture file on your computer. JPEG is a lot like MPEG - both use lossy picture compression algorithms. If the original picture is a 10" X 10" picture, you can shrink it in half one of two ways. The best way is to use Photoshop. Open the file, change the picture size to 5" X 5" and then print it out. It stays digital all the way until the final analog photo on paper. Photoshop has all the original data so it can interpolate the new pixels very accurately. Or you can print out the 10" X 10" picure and then use a photocopier to shrink it. Then its getting converted to an analog picture, scanned back into a digital file, then interpolated, then converted back to an analog print on paper. The first way is like how the HR-20 would do it, and the later is like how your TV must do it. Granted, there is no analog conversion - this is an analogy, so don't dogpile me over that detail! :grin: (postscript - however, all signals sent over component really ARE converted to analog, so there is some truth to the analogy that would apply to both scenarios, I just don't want to introduce that variable to the equation for the sake of this discussion)




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