[opendtv] Re: Math of oversampling
- From: Tom Barry <trbarry@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sat, 23 Apr 2005 10:05:59 -0400
When selling CRT based RPTVs the horizontal scan rate for 1080i is
only 33.75 kHz compared to 31.5 for a 480p version. So it
probably still makes sense as an option for an inexpensive display
format.
But 480i (transmission) -> 1080i really sucks and you probably
don't want to do that.
- Tom
Bob Miller wrote:
> Don Munsil wrote:
>
>
>>From: "Bob Miller" <bob@xxxxxxxxxx>
>>
>>
>>
>>>If a broadcaster uses a 1080p camera and broadcast as 480P and on the
>>>reception end it is upconverted to 720P or stays 480P I understand that
>>>because of oversampling both the 720P or 480P image would be better than
>>>otherwise would be expected. What I would like to do is quantify this
>>>value. How would you compare a straight thru 720P broadcast to one such
>>>as that above. Would the 1080P>480P>720P route be 75% of the quality of
>>>the 720P>720P>720P route? Would 1080P>480P>480P be 110% of 480P>480P>480P?
>>>
>>>
>>
>>It's not something that's simply quantifiable. A very clean 480p image
>>gathered with an excellent 480p camera or telecine could be every bit as
>>good as a 1080p image scaled to 480p. Practically speaking, the 1080p->480p
>>signal will often look better, largely because of preservation of edge
>>sharpness. An image from a 1080p camera downconverted to 480p by a
>>good-quality algorithm like bicubic will probably have better inherent edge
>>sharpness than a raw unsharpened feed of a signal from a 480p camera.
>>
>>On the other hand, judicious application of quality sharpening algorithms to
>>a native 480p image can quite possibly get it to very nearly the 1080p->480p
>>image. It really depends on the cameras, the algorithms, the various formats
>>the picture goes through, etc.
>>
>>
>>
>>
>>
>>>I also have been made to understand that the bit cost of a 480i
>>>broadcast, say X, would not be 2X that of a 480P signal. More like 1.4X
>>>but with the extra juice added by the 1080P acquisition maybe more like
>>>1.5 or 1.6X.
>>>
>>>
>>
>>I assume you mean the opposite - you would expect 480p60 to be 2X the cost
>>of 480i60 (480i30 if you prefer Poynton's nomenclature). Yes, it's not
>>actually 2X the bit rate requirements. The requirements, however, change
>>depending on whether you're talking about deinterlaced 480i60 or native
>>480p60.
>>
>>
>
> I actually switched that before I sent it to make it wrong.
>
> Yes what I want to know is can I approach the quality of HD by sending a
> 480P signal and what is the price in bits above what a 480i quality
> signal would cost percentage wise. I know this has 20 or more variables,
> but what I am looking for is a sense of what the cost would be.
>
> Would a typical customer with a.) a good analog set and b.) a decent
> 42" or smaller HD set be likely to say this looks almost as or as good
> as HD does on the same set.
>
> That is if a customer has a DTV receiver attached to his analog set and
> receives the normal HD programming will other program channels delivered
> in 480P that was acquired in 1080P look as good on his analog set as the
> true HD channels. My guess is yes.
>
> And the same question for the 42" or less HD owner? Can we come close to
> the HD quality that they receive on channel 2 with such a 480P enhanced
> signal? And then what would be the bit cost above a normal SD 480i
> signal. If it is 50% for instance there we have the trade off. For every
> three 480i programs you can only deliver two 480P programs. And then is
> it worth it to the customer of the analog set.
>
> Hey Mr. analog TV set owner get the best of HD, much better than normal
> cable or satellite, on your analog TV set.
>
> And Mr. HDTV set owner get almost the quality of HD and a lot more
> programming on your HD set.
>
> I suspect that the quality increase would be very substantial and the
> cost of losing one third of your program capability may be justified.
>
> I am using my own eyes in judging this having compared ED and HD 42"
> plasmas side by side and not being able to see the difference at a
> comfortable viewing distance when they were both being fed with an HD
> signal.
>
> Bob Miller
>
>
>>Deinterlacing 480i60 to 480p60 doubles the number of MPEG pictures
>>transferred, but the efficiency of both the DCT and the motion estimation
>>goes up because deinterlaced video has higher interframe correlation and/or
>>lower vertical resolution, and I would say somwhere between 1.2-1.5x the bit
>>rate for similar quality is about right, depending on the material. However,
>>1080p60 or 720p60 scaled to 480p60 produces 60 completely independent frames
>>per second, and I would be surprised if you could compress true 480p60 to
>>the same quality with less than 1.6x the bit rate of 480i60, and at times it
>>would require rates closer to 2X. If I had to guess, I'd say 1.6x-1.8x.
>>
>>However, interlaced encoding severely compromises the overall picture
>>quality, especially because of the deficiencies of 4:2:0 interlaced chroma
>>encoding, so perhaps you could pull back the bit rate somewhat and rely on
>>the fundamental visual improvements of progressive encoding to produce a net
>>gain in perceived quality.
>>
>>I would very much guess that most people would be very happy with the
>>quality of true 480p downconverted from 1080p, 720p, or even 1080i. Most of
>>the 480p the public has seen has been deinterlaced 480i (like the 480p our
>>local Fox affiliate was broadcasting last year). Real 480p60 can look
>>astonishingly good.
>>
>>Don
>>
>>
>
>
>
>
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