theora - Dec 2004 - Re: [Theora-dev] Fluendo sample stream and artifacts

Hello!

As I have got no answer on theora-dev, may be the question
belongs more to this list, I'm retrying here:

----- Forwarded message from Ivan Popov <pin@medic.chalmers.se> -----

Date: Thu, 18 Nov 2004 21:50:15 +0100
From: Ivan Popov <pin@medic.chalmers.se>
Subject: [Theora-dev] Fluendo sample stream and artifacts
To: theora-dev@xiph.org

Hello,

I am looking at http://mirror.fluendo.com:8800/ and see the mostly
static test picture, while there are visible artifacts, remarkable e.g.
at the upper border of the violet rectangle (near its upper right corner),
third rectangle from the left in the bottom row.

What puzzles me is why the artifacts are pulsing regularly.
I assume that it is the keyframes frequency, and that
keyframes are relatively imperfect, gradually being perfected by following
corrections.

I was observing a similar phenomenon on other almost-static
theora-encoded scenes as well.

I guess theora is not well suited for static images :)
but I wonder if there are any workarounds or plans to fix this
deficiency, or may be it is a plain bug?

It is a bit annoying that scenes most suitable for compression
become percepted as most distorted.

(I am using mplayer with libtheora from svn 2004-11-18 - that is, today)

Regards,
--
Ivan

----- End forwarded message -----

I would appreciate if somebody explains the reason for the artifacts
and if the encoder can be tuned to avoid or reduce them on static
images.

Thanks,
--
Ivan