[opendtv] Re: Why Europe should choose 720P for HDTV

  • From: Doug McDonald <mcdonald@xxxxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Mon, 13 Dec 2004 09:45:11 -0600

Craig Birkmaier wrote:
> At 11:52 AM -0600 12/12/04, Doug McDonald wrote:
>>Uh, no on that last one. I am seeing blurring that occurs inside
>>the camera. For example, a white line marker in football retains
>>sharp edges with a horizontal pan, and everything else shows
>>the same blurring. Also ... the blurred frames should be
>>much easier to compress since the originals lack
>>much detail at high horizontal frequencies.
> Wrong on both counts.

No, I'm correct.

> IF the lines are sharp, but the objects moving over them are not, 
> then it is NOT the camera.

It's not the "objects" (players) that are moving fast ....
it is the fixed parts of the scene ... teh grid lines and
the fans. This is called a "pan" :-) :-) The players are
much less blurred than the background, at least the guy
carrying the ball ... if teh pan is done right.

> What is happening is that it is easier for 
> the MPEG-2 algorithms to  match blocks where the lines are seen, than 
> it is for the algorithm to deal with random motion. Nothing new here.

No. The "major" motion is not random ... it is the mothing of the
grid lines as the camera pans.

> If you are saying that the lines and the objects that are moving both 
> exhibit the same blurring, then you ARE describing the filtering in 
> the camera.

The grid lines of the field show sharp edges, but are blurred.

This is because, it appears ... and I mean, that is what it looks like
to me ... that the camera has a finite acquistion time, say 1/60 or 
1/100 or 1/200 second.
It appears like it might be some sort of frame transfer device: it 
averages the light for a certain amount of time, and then dumps the
whole picture to a buffer, which is digitized. If so, this would
allow "shutter" times shorter than 1/60 second. And that seems to be
what I sometimes see.


> MPEG-2 encoders can only work as well as the block matching 
> algorithms work. If you can get GOOD predictions (matches), you can 
> make the encoder work MORE efficiently. If you can;t get good 
> matches, then you start to see encoding artefacts.  Eliminating the 
> blur on the edges of moving objects can HELPthe block matching 
> algorithms in an MPEG-2 encoder because it is easier to track the 
> motion precisely. 

The objects I am talking about ... the grid lines ... do have sharp

> I strongly suspect that Fox has tested their entire system from truck 
> to display to determine the best way to use their 720P cameras. They 
> may have run test to determine which shutter speed is best to deliver 
> adequate sharpness in moving objects without stressing the encoders. 
> But there may be more involved in this decision than meets the eye. 
> The 720P source must also be downconverted for the NTSC channel. It 
> could be that the NTSC pictures look better when there is more motion 
> blur (i.e. a lower shutter speed).

Watch ABC or Fox HD football some time on a 720p set. You DO
have an HDTV, don't you, Craig?

Doug McDonald
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