Internet Surfer 2.0/Internet Surfer 2.0 (Wayzata Technology) (1996).iso/pc/text/mac/faqs.208

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Frequently Asked Questions (FAQS);faqs.208



   The standard also provides for other bit rates ranging from 32Kbits/s
   for a single channel, up to 448 Kbits/s for stereo.

Q. What's phase II?
A. As I said, there is a considerable loss of quality in going from
   CCIR-601 to SIF resolution.  For entertainment video, it's simply
   not acceptable.  You want to use more bits and code all or almost
   all the CCIR-601 data.  From subjective testing at the Japan
   meeting in November 1991, it seems that 4 MBits/s can give very
   good quality compared to the original CCIR-601 material.  The
   objective of phase II is to define a bit stream optimized for these
   resolutions and bit rates.

Q. Why not just scale up what you're doing with MPEG I?
A. The main difficulty is the interlacing.  The simplest way to extend
   MPEG I to interlaced material is to put the fields together into
   frames (720x486x30/s).  This results in bad motion artifacts that
   stem from the fact that moving objects are in different places
   in the two fields, and so don't line up in the frames.  Compressing
   and decompressing without taking that into account somehow tends to
   muddle the objects in the two different fields.

   The other thing you might try is to code the even and odd field
   streams separately.  This avoids the motion artifacts, but as you
   might imagine, doesn't get very good compression since you are not
   using the redundancy between the even and odd fields where there
   is not much motion (which is typically most of image).

   Or you can code it as a single stream of fields.  Or you can
   interpolate lines.  Or, etc. etc.  There are many things you can
   try, and the point of MPEG II is to figure out what works well.
   MPEG II is not limited to consider only derivations of MPEG I.
   There were several non-MPEG I-like schemes in the competition in
   November, and some aspects of those algorithms may or may not
   make it into the final standard for entertainment video compression.

Q. So what works?
A. Basically, derivations of MPEG I worked quite well, with one that
   used wavelet subband coding instead of DCT's that also worked very
   well.  Also among the worked-very-well's was a scheme that did not
   use B frames at all, just I and P's.  All of them, except maybe one,
   did some sort of adaptive frame/field coding, where a decision is
   made on a macroblock basis as to whether to code that one as one
   frame macroblock or as two field macroblocks.  Some other aspects
   are how to code I-frames--some suggest predicting the even field
   from the odd field.  Or you can predict evens from evens and odds
   or odds from evens and odds or any field from any other field, etc.

Q. So what works?
A. Ok, we're not really sure what works best yet.  The next step is
   to define a "test model" to start from, that incorporates most of
   the salient features of the worked-very-well proposals in a
   simple way.  Then experiments will be done on that test model,
   making a mod at a time, and seeing what makes it better and what
   makes it worse.  Example experiments are, B's or no B's, DCT vs.
   wavelets, various field prediction modes, etc.  The requirements,
   such as implementation cost, quality, random access, etc. will all
   feed into this process as well.

Q. When will all this be finished?
A. I don't know.  I'd have to hope in about a year or less.

Q. How do I join MPEG?
A. You don't join MPEG.  You have to participate in ISO as part of a
   national delegation.  How you get to be part of the national
   delegation is up to each nation.  I only know the U.S., where you
   have to attend the corresponding ANSI meetings to be able to
   attend the ISO meetings.  Your company or institution has to be
   willing to sink some bucks into travel since, naturally, these
   meetings are held all over the world.  (For example, Paris,
   Santa Clara, Kurihama Japan, Singapore, Haifa Israel, Rio de
   Janeiro, London, etc.)

Q. Well, then how do I get the documents, like the MPEG I draft?
A. MPEG is a draft ISO standard. It's exact name is ISO CD 11172.
   The draft consists of three parts: System, Video, and Audio. The
   System part (11172-1) deals with synchronization and multiplexing
   of audio-visual information, while the Video (11172-2) and Audio
   part (11172-3) address the video and the audio compression techniques
   respectively.

   You may order it from your national standards body (e.g. ANSI in
   the USA) or buy it from companies like
     OMNICOM
     phone [phone]
     FAX [phone]

------------------------------------------------------------------------------

Subject: [72] What is wavelet theory?


Preprints and software are available by anonymous ftp from the
Yale Mathematics Department computer ceres.math.yale.edu[130.132.23.22],
in pub/wavelets and pub/software.

epic is a pyramid wavelet coder. (For source code, see item 15 in part one).

Bill Press of Harvard/CfA has made some things available for anonymous
ftp on cfata4.harvard.edu [128.103.40.79] in directory /pub. There is
a short TeX article on wavelet theory (wavelet.tex, to be included in
a future edition of Numerical Recipes), some sample wavelet code
(wavelet.f, in FORTRAN - sigh), and a beta version of an astronomical
image compression program which he is currently developing (FITS
format data files only, in fitspress08.tar.Z).

An experimental wavelet decomposition program is available
in linc.cis.upenn.edu:/pub/grasp/wavelet.tar.Z.

A mailing list dedicated to research on wavelets has been set up at the
University of South Carolina. To subscribe to this mailing list, send a
message with "subscribe" as the subject to [e-mail].


A 5 minute course in wavelet transforms, by Richard Kirk <[e-mail]>:

Do you know what a Haar transform is? Its a transform to another orthonormal
space (like the DFT), but the basis functions are a set of square wave bursts
like this...

   +--+                         +------+
   +  |  +------------------    +      |      +--------------
      +--+                             +------+

         +--+                                 +------+
   ------+  |  +------------    --------------+      |      +
            +--+                                     +------+

               +--+             +-------------+
   ------------+  |  +------    +             |             +
                  +--+                        +-------------+

                     +--+       +---------------------------+
   ------------------+  |  +    +                           +
                        +--+

This is the set of functions for an 8-element 1-D Haar transform. You
can probably see how to extend this to higher orders and higher dimensions
yourself. This is dead easy to calculate, but it is not what is usually
understood by a wavelet transform.

If you look at the eight Haar functions you see we have four functions
that code the highest resolution detail, two functions that code the
coarser detail, one function that codes the coarser detail still, and the
top function that codes the average value for the whole `image'.

Haar function can be used to code images instead of the DFT. With bilevel
images (such as text) the result can look better, and it is quicker to code.
Flattish regions, textures, and soft edges in scanned images get a nasty
`blocking' feel to them. This is obvious on hardcopy, but can be disguised on
color CRTs by the effects of the shadow mask. The DCT gives more consistent
results.

This connects up with another bit of maths sometimes called Multispectral
Image Analysis, sometimes called Image Pyramids.

Suppose you want to produce a discretely sampled image from a continuous
function. You would do this by effectively `scanning' the function using a
sinc function [ sin(x)/x ] `aperture'. This was proved by Shannon in the
`forties. You can do the same thing starting with a high resolution
discretely sampled image. You can then get a whole set of images showing
the edges at different resolutions by differencing the image at one
resolution with another version at another resolution. If you have made this
set of images properly they ought to all add together to give the original
image.

This is an expansion of data. Suppose you started off with a 1K*1K image.
You now may have a 64*64 low resolution image plus difference images at 128*128
256*256, 512*512 and 1K*1K.

Where has this extra data come from? If you look at the difference images you
will see there is obviously some redundancy as most of the values are near
zero. From the way we constructed the levels we know that locally the average
must approach zero in all levels but the top. We could then construct a set of
functions out of the sync functions at any level so that their total value
at all higher levels is zero. This gives us an orthonormal set of basis
functions for a transform. The transform resembles the Haar transform a bit,
but has symmetric wave pulses that decay away continuously in either direction
rather than square waves that cut off sharply. This transform is the
wavelet transform ( got to the point at last!! ).

These wavelet functions have been likened to the edge detecting functions
believed to be present in the human retina.


Loren I. Petrich <[e-mail]> adds that order 2 or 3 Daubechies
discrete wavelet transforms have a speed comparable to DCT's, and
usually achieve compression a factor of 2 better for the same image
quality than the JPEG 8*8 DCT. (See item 25 in part 1 of this FAQ for
references on fast DCT algorithms.)

------------------------------------------------------------------------------

Subject: [73] What is the theoretical compression limit?


There is no compressor that is guaranteed to compress all possible input
files. If it compresses some files, then it must enlarge some others.
This can be proven by a simple counting argument (see question 9).

As an extreme example, the following algorithm achieves 100%
compression for one special input file and enlarges all other files by
only one bit:

- if the input data is <insert your favorite one here>, output an empty file.
- otherwise output one bit (zero or one) followed by the input data.

The concept of theoretical compression limit is meaningful only
if you have a model for your input data. See question 70 above
for some examples of data models.

------------------------------------------------------------------------------

Subject: [74] Introduction to JBIG


Written by Mark Adler <[e-mail]>.

JBIG losslessly compresses binary (one-bit/pixel) images.  (The B stands
for bi-level.)  Basically it models the redundancy in the image as the
correlations of the pixel currently being coded with a set of nearby
pixels called the template.  An example template might be the two
pixels preceding this one on the same line, and the five pixels centered
above this pixel on the previous line.  Note that this choice only
involves pixels that have already been seen from a scanner.

The current pixel is then arithmetically coded based on the eight-bit
(including the pixel being coded) state so formed.  So there are (in this
case) 256 contexts to be coded.  The arithmetic coder and probability
estimator for the contexts are actually IBM's (patented) Q-coder.  The
Q-coder uses low precision, rapidly adaptable (those two are related)
probability estimation combined with a multiply-less arithmetic coder.
The probability estimation is intimately tied to the interval calculations
necessary for the arithmetic coding.

JBIG actually goes beyond this and has adaptive templates, and probably
some other bells and whistles I don't know about.  You can find a
description of the Q-coder as well as the ancestor of JBIG in the Nov 88
issue of the IBM Journal of Research and Development.  This is a very
complete and well written set of five articles that describe the Q-coder
and a bi-level image coder that uses the Q-coder.

You can use JBIG on grey-scale or even color images by simply applying
the algorithm one bit-plane at a time.  You would want to recode the
grey or color levels first though, so that adjacent levels differ in
only one bit (called Gray-coding).  I hear that this works well up to
about six bits per pixel, beyond which JPEG's lossless mode works better.
You need to use the Q-coder with JPEG also to get this performance.

Actually no lossless mode works well beyond six bits per pixel, since
those low bits tend to be noise, which doesn't compress at all.

Anyway, the intent of JBIG is to replace the current, less effective
group 3 and 4 fax algorithms.

------------------------------------------------------------------------------

Subject: [99] Acknowledgments


There are too many people to cite. Thanks to all people who directly
or indirectly contributed to this FAQ.
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From: [e-mail] (Mark Linimon)
Newsgroups: misc.jobs.contract,news.answers
Subject: Misc.jobs.contract: Frequently Asked Questions (FAQs)
Summary: frequently asked questions about contract jobs on Usenet
Message-ID: <[e-mail]>
Date: 24 Dec 92 08:10:15 GMT
Expires: Thu, 4 Feb 1993 08:09:48 GMT
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Archive-name: contract-jobs/faq
Version: 1.03
Last-Modified: Thu Dec 10 23:59:45 EST 1992

This periodic posting summarizes some of the past discussion in
misc.jobs.contract.  A companion posting, "Welcome to misc.jobs.contract"
<[e-mail]>, serves as an introduction
to the group for new readers.

Misc.jobs.contract is a Usenet newsgroup created to foster exchange of
information about employment on a contract basis, as opposed to employment
on a full-time basis.  Postings specifically addressing full-time employment
should instead be directed to misc.jobs.misc.

Although the group is not _specifically_ dedicated to computer-related
contract work, most of the discussion in the group has related to it.

Please see also the Frequently Asked Question (FAQ) periodic postings
in misc.jobs.misc, misc.jobs.offered, and misc.jobs.resumes, for further
information about the various misc.jobs groups.

------------------------------

Subject: Table of Contents

    Subject: What's the charter of misc.jobs.contract?
    Subject: Is there an archive site for misc.jobs.contract?
    Subject: Should I consider contract work?
    Subject: Don't contract workers make a lot of money?
    Subject: What is telecommuting?
    Subject: What is a job shop?
    Subject: What is Section 1706?
    Subject: What are the tax implications of contract work?
    Subject: Are there other guides for tax questions?
    Subject: Should I incorporate?
    Subject: How can I learn more about computer contract work?
    Subject: Contributions to this posting.

------------------------------

Subject: What's the charter of misc.jobs.contract?

When originally chartered, it was for postings of contract jobs available,
contract jobs offered, and discussion of contracting in all its forms.
At the time it was felt that one group would be sufficient, and if
traffic mandated, it could later be subdivided along the lines of
misc.jobs.contract.[offered,resumes,misc], to mirror the upper-level
groups.  [This latter was never official, and from my own anecdotal
recollection -- mcl].

------------------------------

Subject: Is there an archive site for misc.jobs.contract?

Not that I'm aware of.

------------------------------

Subject: Should I consider contract work?

Contract work appeals to a certain type of individual.  Although it's
somewhat risky to generalize, the most important traits would include:
being a self-motivated individual; willingness to trade personal security
for risk; dealing well with people; and technical ability.  You may well
find that the first three issues are more important to success than the
latter.

You should seriously consider getting advice from a qualified CPA and a
qualified lawyer _before_ making the move.  The issues involved are
complex, the risks significant, and advice you get on the net (while
some of it is excellent) should be taken with a grain of salt.  This
explicitly includes this posting.

------------------------------

Subject: Don't contract workers make a lot of money?

Yes, but the expenses are much higher.  An oft-quoted rule of thumb is
that one should make about 2x the amount one would expect as a full-time
employee, just to break even.  Factors such as the self- employment tax,
paying for one's own medical expenses, equipment, sick time, vacations,
and time between jobs consume the difference.

You may encounter resentment from some full-time employees who under-
estimate the value of these things as well as other intangibles, such
as the (very real) risk of not being paid.

------------------------------

Subject: What is telecommuting?

This is an arrangment with a company where one maintains equipment at
one's own residence or office and works remotely, by modem.  Tele-
commuting is not widespead as of yet but may be on the increase.  Both
contract work and full-time work have been known to be done this way.
As above, intangibles such as one's personal relationship with the
company and communications skills with others take on a much more
important role than one might expect.

------------------------------

Subject: What is a job shop?

A job shop is a company that hires employees who are themselves on either
a contract basis or full-time basis, and contracts them out to other
companies.  Some operate merely as referral services, who get a cut of
the employees' hourly rate; some have such amenities as sick time,
vacations, and 401k plans; most fall somewhere in between.  Before you
go to work at a job shop as a contract employee (as compared to full-
time employee), be prepared to consult a CPA or attorney about the
implications of Section 1706.

------------------------------

Subject: What is Section 1706?

This is a section of the U.S. tax code that makes it difficult for
anyone receving employment through a job shop to be considered as a
contract worker.  Instead it presumes that such individuals are full-
time employees unless a set of criteria are met.  A companion posting
to this one, "Misc.jobs.contract: Text of IRS Section 1706"
<[e-mail]>, contains the entire text.

------------------------------

Subject: What are the tax implications of contract work?

Some brief guidelines for taxes in the United States are presented in
the following paragraphs.  Again, it is mandatory that you get advice
from a qualified CPA or tax practitioner, of which your current humble
Poster is neither.

The general concepts of tax for small business are explained in Internal
Revenue Service Publication 334, "Tax Guide for Small Business".

As a self-employed person, you will need to file estimated taxes.
The concept of estimated tax is explained in IRS publication 505,
"Tax Withholding and Estimated Tax".  You will need to file estimated
taxes on form 1040-ES every quarter to avoid incurring hefty penalties.

If you are self-employed, each client will send you a Form 1099 at the
end of the year, not a Form W-2.

If you are self-employed, you pay double FICA (Social Security) tax,
currently 15.3%.  This is paid with your estimated taxes and on your
regular form 1040.

If you are self-employed, you will possibly also want an Employer ID
Number to give your clients, rather than your own Social Security Number;
the EIN is assigned by the IRS when you apply on form SS-4 (available
from the IRS, not the Social Security Administration).  Using an EIN
rather than your SS is apparently only a _necessity_ in certain cases.

Arthur L. Rubin ([e-mail]) clarifies:

    You only need an EIN (and state ID number) if you have employees,
    have a "qualified retirement plan", or want to qualify for certain
    other tax credits, which I would think most consultants wouldn't be
    able to qualify for anyway.

    If you incorporate or form a consulting partnership (I don't see any
    advantage to a partnership, but it is legal), you need an EIN.

IRS forms and publications are available free by calling 1-800-TAX-FORM.
Service is normally pretty prompt: one to two weeks.

Also, check with the Secretary of State of your home state.  You may
have to pay worker's compensation or unemployment taxes, and possibly
obtain other business licenses and permits.

------------------------------

Subject: Are there other guides for tax questions?

There is a tax guide for just about all engineering tax questions,
recommended by [e-mail] (Pete Holzmann).  It is put out by a
non-profit organization (Academic Information Service, PO Box 400,
Greenbelt MD 20770) and is called "Tax Guide for Engineers".   Here's
a few key aspects of this annual guide:

    If it doesn't save you at least $200 in taxes, you're welcome to
        ask for your $$$ back ($24.95 list).
    It is specifically oriented towards technical professionals who
    may or may not have a side business.
    They actually research tax court cases to find out what the courts
        think, rather than just what the IRS says.
    They provide a really good framework for filling out taxes that
        tends to minimize audits.

------------------------------

Subject: Should I incorporate?

Again, as above, the best thing you can do is to get advice from a
qualified CPA and a qualified lawyer.

Opinions are divided on this issue: Some consultants believe incorporation
is a waste of time and money; others believe it is necessary.  Opinions
also vary as to whether incorporation protects you from Section 1706
(see below).

------------------------------

Subject: How can I learn more about computer contract work?

This newsgroup is only one source of information.  There is a moderated
SIG on Compuserve run by ICCA, the Independent Computer Consultants
Organization, 1-800-GET-ICCA, which also publishes a good newsletter.
There is also a CONSULT forum on Fidonet [details please? mcl].
[There are bound to be other such organizations -- please email me.]

Also, three magazines that deal mainly (but not exclusively) with listings
of jobs available through job shops are:

      CE [Contract Employment] Weekly
      C.E. Publications Inc.
      P.O. Box 97000
      Kirkland, WA, USA 98083-9700
      phone [phone]
      fax   [phone]

      Technical Employment News (formerly PD News)
      Publications & Communications, Inc.
      P.O. Box 399
      Cedar Park, TX, USA 78613
      phone [phone] or [phone]
      fax   [phone]

      NTES Hot Flash
      published by National Technical Employment Services
      P.O. Box 217
      Scottsboro, Alabama, USA 35768
      phone [phone]
      fax   [phone]

[There are bound to be others.  As above, email me and I'll include them
in future editions of this message.]

------------------------------

Subject: Contributions to this posting.

I would like to thank the following people, who have contributed to, or
helped revise, this posting:

    Robert Blythe ([e-mail])
    Stan Brown (abvax!iccgcc.DNET![e-mail])
    Pete Holzmann ([e-mail])
    Chip Rosenthal ([e-mail])
    Arthur Rubin ([e-mail])

[Obligatory disclaimers: I have no connection, other than subscriptions,
with the above magazines; however, I am an ICCA member.  I've made my best
effort to ensure all information is correct, but errors have been known to
occur.]

This posting is subject to comment and improvement by sending email to
[e-mail].
--
    Mark Linimon / Lonesome Dove Computing Services / Roanoke, Virginia
   {chinacat,uunet}!nominil!linimon   ||    [e-mail]
     "I keep my fingernails long, so they click when I play the piano."
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From: [e-mail] (Mark Linimon)
Newsgroups: misc.jobs.contract,news.answers