Color Depth

[Guest]

Archived from groups: alt.tv.tech.hdtv (More info?)

I have a new HDTV, but when watching HDTV it looks like a picture when
your reduce the color depth. Especially the reds. For example a red
flag, the differences in the reds is not a smooth transistion, but
instead distinct lines from one to another. Is this normal? Is this
due to lack of signal strength? Would the problem be with the cable
box or TV?
(The cable company stated they will charge $50+ if the problem isn't
them.)
Thanks for your help!

 

[Guest]

Archived from groups: alt.tv.tech.hdtv (More info?)

You could consider this a jpeg artifact.

 

[Guest]

Archived from groups: alt.tv.tech.hdtv (More info?)

On 27 Sep 2005 20:25:33 -0700 Samuel Schweighart <schwghrt@mit.edu> wrote:

| I have a new HDTV, but when watching HDTV it looks like a picture when
| your reduce the color depth. Especially the reds. For example a red
| flag, the differences in the reds is not a smooth transistion, but
| instead distinct lines from one to another. Is this normal? Is this
| due to lack of signal strength? Would the problem be with the cable
| box or TV?
| (The cable company stated they will charge $50+ if the problem isn't
| them.)
| Thanks for your help!

Uh ... TV is a bunch of pictures.

If you reduce the color depth to just 2 colors, you'll have only ON and
OFF. That will be rather obvious. If there are 4 colors, it will be
closer to viewable, but you will still see the very gross banding. This
is all part of what happens with digitizing of smooth analog levels into a
finite set of digital levels. The idea is to have enough levels so that
the effect is not seen on most scenes (or ideally on any scene). Some
people think 256 levels is enough. Others think 1024 is needed. You are
not going to have smooth transitions with digital, but if you get enough
of them, it can appear smooth to the human eye.

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[Guest]

Archived from groups: alt.tv.tech.hdtv (More info?)

On 27 Sep 2005 20:25:33 -0700, "Samuel Schweighart" <schwghrt@mit.edu>
wrote:

>I have a new HDTV, but when watching HDTV it looks like a picture when
>your reduce the color depth. Especially the reds. For example a red
>flag, the differences in the reds is not a smooth transistion, but
>instead distinct lines from one to another. Is this normal? Is this
>due to lack of signal strength? Would the problem be with the cable
>box or TV?
>(The cable company stated they will charge $50+ if the problem isn't
>them.)
>Thanks for your help!

Is this mosty visible on HDTV signals?
So far I have only access to (european) SDTV via satellite.

If you freeze such pictures it normally looks terrible.
But I would say that the banding is not normally visible altough with
some content there are banding in gray levels, typically around bright
lights in a dark scene.

This is probably an effect of the data reduction (MPEG compression).
Since HDTV increases I resolution but not the comression ratio, I like
to add a question:

Does HDTV-signals generally show more or less of the MPEG artifacts
like banding and blocking compared to digital SDTV-signals?

/Jan