2-hour length, 148.50 Mhz, 1920 x 1080 progressive scan image, 1-bit object data, 193 bits of file s

[Richard Crowley]

Can anybody explain what is the point of this whole
"discussion"? It seems to me like one of the most
ridiculous wastes of time that has come along here
in months/years.

 

[Martin Heffels]

No, let's try this another way.

Sorry, I was a bit short in my answer, but I understood what you said
My bad.

-m-
--

 

[Martin Heffels]

Doesn't matter. Again, the compressed stream is delivering data
at a rate which, relative to the original pixel rate, represents less
than one bit per pixel on average.

But this is a bit weird comparison. After all, a normal colour-image on tv,
can not be represented by 1 bit pieces. It would be better to speak in
terms of bytes, and then a compression-ratio makes more sense.
When I am compressing an video-image, I am not throwing away 7 bits and
keep 1. No, I throw away bytes which are occuring repeatedly (lossless), or
similar in colour (lossy).

-m-
--

 

[Ken Maltby]

Can anybody explain what is the point of this whole
"discussion"? It seems to me like one of the most ridiculous wastes of
time that has come along here in months/years.

Agreed.

 

[Pasi Ojala]

When I am compressing an video-image, I am not throwing away 7 bits and
keep 1. No, I throw away bytes which are occuring repeatedly (lossless), or
similar in colour (lossy).

When someone else is doing video compression (btw, it not
AN image, video compression handles multiple images), it is
much more than that.

There's delta coding (differences between frames), transform coding
(for example DCT) and quantization (represent data that matters most
more accurately). And/or prediction and encoding only prediction error.

After this lossy phase you use lossless entropy codes.

-Pasi

 

[Bob Myers]

But this is a bit weird comparison. After all, a normal colour-image on
tv,
can not be represented by 1 bit pieces. It would be better to speak in
terms of bytes, and then a compression-ratio makes more sense.
When I am compressing an video-image, I am not throwing away 7 bits and
keep 1. No, I throw away bytes which are occuring repeatedly (lossless),
or
similar in colour (lossy).

Doesn't matter whether you talk about bits, bytes, words,
characters, or squamishes (a word I just stole from an old
Mad magazine to refer to data organized in 43-bit chunks).
You start out with this many bits, you wind up with this many
bits. It's just that "average bits per displayed pixel" has been
one of those fun ways of presenting compression ratio
information, especially in seminars where the objective of
the presenter is to elicit a "wow!" response from the audience
which is presumably learning about this stuff for the first time.

And you're never simply throwing away bits or bytes in
any practical compression scheme which is currently in
use; that would be far too crude. What happens in real-
world systems is far more complicated, and produces a
far better result.

Bob M.