|
|
Posted by Tim Smith on 01/13/07 04:23
In article <Qe2dnZVs-ovroDXYnZ2dnUVZ_vKunZ2d@comcast.com>,
> >> Right, and this was in the same fantasy world you live in where a
> >> 720x576 DVD cannot be fully resolved except by a 1440x1152 display?
> >> Did you happen to see a unicorn out your window while you were
> >> playing it?
> >
> > Plonk.
>
> Oh good, you've killfiled me. That saves me the effort of having to
> correct your ridiculous stream of misinformation. Have fun living in
> that fantasy bubble of yours.
>
> To anyone else reading this thread, know that Mr. "M.I.5" has
> absolutely no idea what he's talking about.
Actually, there *may* be something to his claim, in an obscure set of
circumstances. Consider for a moment a CRT display. If you put up an
image consisting of a grid of lines that are one pixel wide, and look at
those lines with a magnifying glass, you'll find that the pixels aren't
mapped one-to-one to phosphor triads. (Even without looking with a
magnifying glass, a moment's thought and playing with the CRT controls
will make this apparent. If you play with the image size controls, you
can smoothly shrink or enlarge the image, but the phosphors are fixed,
so it is the mapping from pixels to phosphors that is changing).
For an LCD display, or a DLP display, or a plasma display, you'd expect
there to be a one-to-one mapping from input pixels to device pixels.
However, that is not always so. My DLP, for example, has two modes it
can use when displaying a 1280x720 input. One is called TV mode and one
is called PC mode. The explanation they give is that the system is
designed so that 1280x720, at a one-to-one mapping, is slightly larger
than the screen, to match the overscan of conventional televisions. In
PC mode, it maps the 1280x720 input pixels to a slightly smaller set of
pixels on the display, so that they will all be visible.
It does a very good job of this. It's got good antialiasing software.
But it is not perfect. You can tell that you've effectively lost some
resolution.
Now imagine that I had a 2560x1440 display instead, and it had TV and PC
modes. It it accepted a 1280x720 signal in PC mode, and scaled it up to
something slightly smaller than 2560x1440, I think it could do that in a
way that would look a lot better than the 1280x720 display does when it
shrinks the image slightly.
So, if he is using a display technology where there is not a one-to-one
mapping from input pixels to device pixels (such as a CRT, or a display
in some kind of scaling mode), then a 1440x1152 display could actually
do a better job than a 720x576 display at displaying 720x576 DVD images.
For a display where there is a one-to-one mapping, it might be possible
to make it so that a DVD looks subjectively better at 1440x1152 than at
720x576. Each pixel from the DVD would be mapped to 4 pixels on the
display. If those are mapped in the simplest possible way--the 4 pixels
all take the same value, then I don't think there will be much
difference. You've just made bigger pixels. Although I suppose we
should probably consider the arrangement of subpixels on an LCD.
Representing each image pixel by 4 device pixels might make it so that
artifacts due to subpixel structure might be less visible.
However, suppose the device doesn't use the simplest possible mapping?
Consider 3 2x2 pixel squares on the device, arranged in an L shape. I'll
name these pixels A, B, C, ..., P in the drawing below. And consider 4
image pixels, which I'll name 1, 2, 3, 4:
A B C D
1 2
E F G H
I J K L
3 4
M N O P
In the simplest mapping, we'd set ABEF all to the value of 1, CDGH all
to 2, and so on. But how about instead setting each device pixel to a
blend of the nearest 4 image pixels? F, for example, is nearest 1,
followed by 2 and 3, and then 4. So set it to a weighted mix of those
four pixels, weighted by some function of distance.
I could see this looking better, especially if you are viewing too close
to the display, so that various artifacts are visible.
The 1440x1152 display wouldn't be displaying MORE information than the
720x562 display, so his claim about fully resolving the DVD would not be
correct, but it could look better in the cases I've mentioned above, and
that could be what he is seeing.
--
--Tim Smith
Navigation:
[Reply to this message]
|