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

  • From: Craig Birkmaier <craig@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Mon, 13 Dec 2004 12:24:29 -0500

At 9:45 AM -0600 12/13/04, Doug McDonald wrote:
>  > 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.

Then this is a third situation, not the one you described previously. 
You can pan on a wide shot or on a close-up. The tighter the shot, 
the more the background will appear blurred.

In this situation the background is blurred and the moving foreground 
object is being tracked by the camera, causing it to appear more 
sharp than the background.

In this case, the moving objects (players) should be sharper than the 
background; this is just the opposite of what you described 

>>  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.

This is NOT the major motion. It is minor, predictable motion along a 
single vector, unless the camera is also zooming, in which case the 
motion become very complex for MPEG-2 to track. In either case, 
tracking the lines on the field is a piece of cake, compared to 
dealing with the players that are moving in multiple directions while 
twisting and turning, which reveals new information that was not 
previously available for block matching.

>>  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.

As I mentioned in another post, I suspect Fox has been playing with 
shutter speeds to determine which speeds provide optimal sharpness 
without stressing the MPEg-2 encoder.

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

Now they are sharp again. Just a moment ago you said "The grid lines 
of the field show sharp edges, but are blurred."

Yes, the stimulus is a sharp edge, but the blurring is caused by the 
movement of the camera, which causes the leading and trailing edges 
of the line to move over the sensor, causing blurred edges. The 
center of the line is also blurred, but you can't see this because it 
appears as a white solid, rather than a textured area of grass blades 
painted white.

>  > 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?

I have the display, but I do not have a receiver...yet. I have seen a 
little of this source in stores. I would expect that the images are 
quite similar for Fox, ABC and ESPN, since they are all using the 
same cameras (Grass Valley World Cams). I have watched the NTSC 
downconversions, after they have been de-interlaced by my HD monitor. 
They look good, but are clearly not HDTV. The slo motion stuff looks 
better on both NTSC and HD.

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