[opendtv] Re: Math of oversampling
- From: Bob Miller <bob@xxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 22 Apr 2005 16:24:38 -0400
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
>
>
----------------------------------------------------------------------
You can UNSUBSCRIBE from the OpenDTV list in two ways:
- Using the UNSUBSCRIBE command in your user configuration settings at
FreeLists.org
- By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word
unsubscribe in the subject line.
Other related posts:
