[opendtv] Re: Mediaflo Technology

  • From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Sun, 12 Nov 2006 17:43:48 -0500

Mark Schubin wrote:

> Starting at the top left is a curve like the right side of a
> bell-shape. It's a modulation-transfer-function (MTF) curve. It
> ends up at the bottom right, but the exact shape of that curve
> is determined by such factors as the number of samples in the
> display. Anything above that curve simply isn't reproduced by
> the system.
>
> The two curves intersect. Where the visual system needs the most
> contrast, the television system provides the least (i.e., where
> the CSF curve is highest, the MTF curve is lowest). There is a
> wedge at the left side of the grating, which is both visible
> (above the CSF curve) and reproduced (below the MTF curve).
> EVERYTHING we see from a particular television system must fit
> within that wedge. It's pretty scary.

One way to increase MTF, given that lenses are not cheap, is to increase
the area of the sensor, as we discussed some time ago. (Parenthetically,
I don't understand why this point isn't driven home in Popular
Photography magazine. It seems like a very simple point to make to an
interested consumer, and the reasons are not difficult to explain
either.)

Audio analogies help, for me. I think what you're saying here is that an
amplifier that only reproduces low frequencies with reasonable output
power will miss the parts of the audio spectrum that human hearing is
most acute.

A dramatic example of this would be a subwoofer. It can reproduce high
"contrasts," i.e. a lot of output power, only at frequencies up to,
typically, 100 Hz or so. However, human hearing discerns most clearly
frequencies between, say, 50 and 5000 Hz (1000 Hz being the perceived
middle).

Which is why if one listens only to the output of a subwoofer, there is
not a lot of usable info there. Just muffled stuff.

The MTF curve you show in Slide 7 looks subjectively much like the
output surve of a subwoofer amp.

> We have no control over a viewer's CSF. The only way to increase
> the size of the wedge is to increase the MTF. More samples is
> one way to do that.

And increase the size of the sensor or increase the quality of the lens,
or both.

Bert
 
 
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