[Tig] video compression: lossless? (JPEG2000)
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.
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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