Questions about de-interlacing 1080i - AVS Forum
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post #1 of 8 Old 01-12-2010, 10:30 PM - Thread Starter
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I'm not sure if this is the right place but I had a few question about de-interlacing 1080i.

1. I talked to a 3 different best buy reps and they all told me that no LCD TV will take a 1080i tv signal and de-interlace it to 1080p. Is that true, because for the longest I thought samsungs, sony's etc video processor in their newer LCD TV's were able to do so.

2. When de-interlacing 1080i 30 fps to 1080p, does it result in 1080p30fps, or by combining the separate odd and even fields, do you get 1080p 60fps?

3. If it does de-interlace to 1080p 30fps, what do you need to have to change the scan type from 30fps to 60fps.

4. Is there a difference between sourced 1080p compared 1080i that has been deinterlaced to 1080p.


I have done some research but I can't find any clear answers to these. If someone is able to help me out with these questions, I would really appreciate it. Thx in advance.
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post #2 of 8 Old 01-13-2010, 12:59 AM
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no LCD TV will take a 1080i tv signal and de-interlace it to 1080p.

That's crap, since the LCDs are running natively in 1080p, the 1080i is definitely being deinterlaced - one way or the other. Also all newer LCDs will do this quite good on movie material. Video material is a bummer though on most displays.

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When de-interlacing 1080i 30 fps to 1080p, does it result in 1080p30fps, or by combining the separate odd and even fields, do you get 1080p 60fps?

To be exact there's no 1080i30, only 1080i60. For movie material it gets deinterlacing to 1080p60 with 24 genuine pictures iterated in a 3:2 cadence. For video material (sports) you get 1080p60 with 60 genuine phases of movement. Don't think of the "wrong" p30 deinterlacing which is usually done using PC software.

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Is there a difference between sourced 1080p compared 1080i that has been deinterlaced to 1080p.

for movie material there is no difference since the 1080i60 stream contains all full frame imagine. For live video material, you get double the vertical resolution per 1/60sec. Think of the 1080i60 stream of 540p60 instead. Good video deinterlacers (external processors) will calculate an amazing amount of detail out of this signal, while TVs themselves often just upscale the 540p fields without adding any detail - that's likely what your sales reps meant in the first place.


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post #3 of 8 Old 01-13-2010, 12:16 PM
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for movie material there is no difference since the 1080i60 stream contains all full frame imagine. For live video material, you get double the vertical resolution per 1/60sec. Think of the 1080i60 stream of 540p60 instead. Good video deinterlacers (external processors) will calculate an amazing amount of detail out of this signal, while TVs themselves often just upscale the 540p fields without adding any detail - that's likely what your sales reps meant in the first place.

To clarify, for progressive source material shot on film or progressive digital cams- each 1920x1080 camera progressive frame is split into an odd field containing rows 1,3,5...,1079 and an even field (half frame) containing rows 2,4,6,...,1080. These fields are displayed sequentially every 1/60 of a second as 1080i60- so the same instant in time orginally captured by the camera (film or progressive digital cam) is now split into two instances in time.

These odd and even "540p" fields in the 1080i60 signal can be inverse telecined back to 1080p60. The original progressive frames are reconstructed from the two 540p fields (odd+even rows of pixels) that were split in two fields when telecined, or interlaced. Recombining like this is known as "weave" deinterlacing.

Simple upscaling one 540p field without weaving is known as "bob" deinterlacing.

For 1080i60 signals recorded with 1080i cameras, you need a motion adaptive deinterlacing chip to achieve maximum detail and avoid bob deinterlacing.

As for the specific questions:

1. I talked to a 3 different best buy reps and they all told me that no LCD TV will take a 1080i tv signal and de-interlace it to 1080p. Is that true, because for the longest I thought samsungs, sony's etc video processor in their newer LCD TV's were able to do so.

>> First mistake- BB is the WORST place to ask for advice. Common knowledge around here.

All 1080p displays MUST deinterlace somehow to display 1080i60 fullscreen. Most sets probably just bob each 1920x540 field to create a 1920x1080 frame, basically doubling every row of pixels. Better sets will do 3:2 pulldown/weave to re-create progressive frames from progressive source (shot with progressive/film cameras) and do motion adaptive deinterlacing on 1080i source (shot with interlaced cameras). The best sets will also remove judder by eliminating the 3:2 cadence of inverse telecined (weaved) progressive sourced material, displaying at an even multiple of 24fps (display at 48Hz, 72Hz or 120Hz).

2. When de-interlacing 1080i 30 fps to 1080p, does it result in 1080p30fps, or by combining the separate odd and even fields, do you get 1080p 60fps?

>> Already answered- 1080i30 doesn't exist in normal commercially available video sources. 1080i is always 60 (and maybe 50) *fields* per second (1920 columns x 540 odd rows the first 1/60 of a second, then 1920 columns x 540 even rows of pixels the next 1/60 of a second and so on).

3. If it does de-interlace to 1080p 30fps, what do you need to have to change the scan type from 30fps to 60fps.

>> Again, don't confuse *fields* (interlaced) per second with *frames* (progressive) per second.

4. Is there a difference between sourced 1080p compared 1080i that has been deinterlaced to 1080p.

>> Again, if the material is shot with an interlaced camera, you need motion adaptive deinterlacing to improve detail beyond 1920x540 (for moving images). If the material is shot with a film or progressive digital camera, weave deinterlacing is all that is needed (and 3:2 pulldown for 24 frame per second originating material).


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post #4 of 8 Old 01-14-2010, 09:11 PM - Thread Starter
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thx alot for the helpful responses.
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post #5 of 8 Old 01-14-2010, 10:17 PM
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Quote:
Originally Posted by RapRepoMan2 View Post

1. I talked to a 3 different best buy reps and they all told me that no LCD TV will take a 1080i tv signal and de-interlace it to 1080p.

What a great reason to never shop at Best Buy again! What chumps...
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post #6 of 8 Old 01-23-2010, 07:36 PM
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Originally Posted by RapRepoMan2 View Post

1. I talked to a 3 different best buy reps and they all told me that no LCD TV will take a 1080i tv signal and de-interlace it to 1080p.

I wish I could say that one in four LCD HDTV's could take a 1080i TV signal and de-interlace it well (including with motion adaptive de-interlacing) to 1080p.

Alas I am led to believe that (admittedly having done no recent research) as of early 2010 fewer than one in 20 do.

If the TV filled in the odd scan lines (rows of pixels) with the incoming odd field while leaving the even scan lines untouched, and then filled in the even scan lines with the incoming even field while leaving the odd scan lines untouched, then we get defacto weave de-interlacing. This preserves all of the vertical detail but we get an uncanny feathered blur on the sides of moving objects. Experts have considered interpolation (upscaling; bob) as the lesser of evils when dealing with the parts of the picture representing movement.

Good motion adaptive de-interlacing tries to do weave on the stationary material and bob on the moving material regardless of the shape, size, or number of these spots on the screen.

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4. Is there a difference between sourced 1080p compared 1080i that has been deinterlaced to 1080p. ).

There is no difference format wise. Quality wise the detail of "moving" subject matter in 1080i after de-interlacing is pretty much limited to what individual fields contain which is half the vertical resolution of what sourced 1080p would have.



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post #7 of 8 Old 02-05-2010, 01:05 PM
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If each field of a 1080-60i is 1/60 of a second it takes two fields or 2/60 of a second to get one frame. The frame can doubled to achieve 1080-60P. I can't see getting a whole frame with and odd and even field (2) in 1/60 of a second.
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post #8 of 8 Old 02-05-2010, 07:41 PM
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two ways to see it:

a) cheaper deinterlacers, especially for video material (not film) just use single fields to create full frames, creating 1080p60 from a 1080i60 input.

b) with a good deinterlacer, you want to create 60 frames from 60 fields nevertheless. Every field is used two times, one time with it's predecessor, one time with it's successor. You get a delay of at least 1 field, but after that you'll still get a full frame every 1/60sec.

Only the most basic (and bad!) PC-software-based deinterlacers create a 1080p30 output from a 1080i60 video (!) input. Your idea seems to be based on this theory. With standalone processors this is something you don't have to deal with though.


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