Re: WHOA!! Backup the JPG truck...

[P3D Michael Kersenbrock <michaelk@xxxxxxxxxxxxxxxxxx>]

> There are two major advantages to JPEG over alternative formats:
> 1. It is a well accepted standard.
> 2. It allows variable compression while maintaining spatial resolution.
> 
> Because there are many well accepted defacto standard image formats, if
> you don't use JPEG's image compression, I think you are giving up most
> if the advantage.

In a practical sense, JPEG's replaced .GIF's as "the" standard in popular
use.  Jpeg's also had the advantages of not stepping on the LZW compression
patent and had the advantage of 24-bit color support which .GIF didn't.
That it had higher levels of compression for most images was an additional
plus, but not wasn't it's only advantage for a common-use standard. Other
"standards" like .PCX were proprietary. .BMP's isn't even run-length
compression (as well as being something from the M* company), and .TIF 
has/had a lot of incompatible versions. Jpeg's were new and made by 
committee so it wasn't proprietary or multi-versioned.

> Then I guess the answer is no, people are not publishing high quality
> images on the web in JPEG or JPS format, although they may be creating
> them in the privacy of their own homes.  Perhaps this is why Dr. T and

Someday when the "everyone's" access speed is T1 speed or better, things'll
be better.  Otherwise <expletive deleteds> come from those with analog
modems.  :-)

> > I'm not at all sure why anyone would want to store separate 8 bit
> > channels other than scientific curiosity. What's the point?
> 
> The point is that data compression techniques work by finding redundant
> patterns in the data and substituting short codes to replace long
> sequences of bits.  If you take an image with 24-bit color and separate
> it into 8-bit channels, each of the channels will usually contain much
> more redundancy the original 24-bit image.
> 
> Take a long list of full names.  If you try and compressing it by coding
> all of the John Smiths as 1, and all of the Jane Does as 2  there is
> likely to be little redundancy, depending on where the list of names
> came from.

For simple compression schemes your example is a good one, however the
commonly used compression schemes will have codes for each sub-string
and so whenever "John" shows up (even attached to another last name) that
code will be used.  Even everyday compression schemes (LZW, etc) are 
pretty good.  SOME improvment can be had by rearranging things, but not
as dramatic of a one that your example might suggest.  Perhaps your
example was made more dramatic to make a point, if so, "never mind".  :-)

> On the other hand, lossy compression techniques, such as JPEG and JPS,
> when they dont find enough redundancy in an image,  blur the colors to
> create some.  Apply the name list metaphor to JPEG, and Jonathan Gross
> and Larry Berlin might come out John Grossman and Lance Berman.  Close
> enough? 

Well... it'd probably be more like Lary Berlin and John Grosman.  It's the
details that become missing, not usually the big chunks unless it's turned
up REALLY high.

What ever became of the company coming out with fractal compression that
was supposed to REALLY compress images but with good fidelity?  Haven't
heard much from them lately.  Must be more than five years since they had
their 15-minutes in the national limelight.

Mike K.


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