[Tig] video compression: lossless? (JPEG2000)

Bob Friesenhahn bfriesen at simple.dallas.tx.us
Sun Oct 18 17:58:51 BST 2009


On Sun, 18 Oct 2009, Rob Lingelbach wrote:
> count me as one who didn't know that Bob. So "video" is synonymous with 
> "consumer video"  and in referring to production or post-production at a 
> certain budget level, we don't use "video" but we use "motion picture."   If 
> you have any references on this distinction please pass them along, I'd like 
> to include them on the TIG.

Consider the reference to now be created. :-)

Almost anyone contributing to Wikipedia who uses the term "video" is 
certainly describing lower-bandwidth stuff such as comes out of a 
video camera, VCR, DVD, broadcast TV, etc.  The term "video" is most 
often used for YCbCr encoded (a form of compression), and (usually) 
subsampled (more compression) stuff.  I am simply trying to interpret 
the reason for the claim for you.

A Wikipedia claim that "video is almost always compressed" is surely 
wrong if Cineon/DPX files from datacine/scanner are considered to be 
"video" since such content is in common use.  However, if they are 
"video" then the WikiPedia claim is incorrect or incomplete.

> Wouldn't a file-to-file copy of bits, not using compression, be lossless, 
> assuming no bits are lost?

Nope.  As soon as you introduce the notion of a 'bit', you have 
introduced the notion of quantization, which is compression using 
'bits'. Only analog reality is uncompressed.

>> So one can see that JPEG 2000 lossless still leads to 2X compression ratio, 
>> but the image can be compressed quite a lot (and still look pretty good).
>
> that's impressive.  But by that last parenthetical phrase are you perhaps 
> suggesting that something was lost?  :)

Yes, of course.  I see that even for the "lossless" case there is a 
tiny measurable difference, which could indicate a bug in 
GraphicsMagick or the Jasper (JPEG2000) library.

Bob
--
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/




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