[tig] VIPER, anyone?

Martin Euredjian ecinema
Mon Jun 30 02:42:15 BST 2003


Bill Hogan wrote:

> Anything besides the vertical over sampling then vertical filtering
> to the desired 720 or 1080 vertical lines.

Bill, don't fall prey to marketing spin. :-)

The Viper does not oversample vertically.  It's a, shall we say, standard
CCD that is being driven cleverly in order to achieve different native
output resolutions.  The definition of a pixel, in the context of CCD's is a
function of how the array is driven, rather than strictrly delimited
structural components on the chip.  The "pixel" is formed through the
adequate excitation and creation of potential barriers (voltage) that
constrain collected charge to an area that can then be bucket-brigadded out
of the chip.

Let's try some ASCII art.  If the diagram below represents one corner of the
CCD:

col:0    1    2    3    4    5
    |    |    |    |    |    |
R00 +----+----+----+----+----+-
R01 +----+----+----+----+----+-
R02 +----+----+----+----+----+-
R03 +----+----+----+----+----+-
R04 +----+----+----+----+----+-
R05 +----+----+----+----+----+-
R06 +----+----+----+----+----+-

The numbering refers to the rows and columns, literally conductors used to
control potential.

If you use three rows to delimit a pixel:

col:0    1    2    3    4    5
    |    |    |    |    |    |
R00 +----+----+----+----+----+-
R01 +    +    +    +    +    +-
R02 +----+----+----+----+----+-
R03 +    +    +    +    +    +-
R04 +----+----+----+----+----+-
R05 +    +    +    +    +    +-
R06 +----+----+----+----+----+-

Then where I've blanked-out row dashes above is where the charge for a pixel
will be corralled prior to shifting it out.  This gives you one possible
vertical sampling resolution.

However, if you use four rows:

col:0    1    2    3    4    5
    |    |    |    |    |    |
R00 +----+----+----+----+----+-
R01 +    +    +    +    +    +-
R02 +    +    +    +    +    +-
R03 +----+----+----+----+----+-
R04 +    +    +    +    +    +-
R05 +    +    +    +    +    +-
R06 +----+----+----+----+----+-

Your "pixels" just grew verticall, hence a different vertical resolution for
the same chip.

The Viper is, for the most part, a standard LDK video camera with the
addition of the uncompressed data output hardware.  I haven't looked at the
marketing material in quite some time, but I remember them listing the
number of ROWS in chip as though it were vertical resolution.  Hence
oversampling.  Well, any CCD, from the one in a $5 Barbie-Cam to any
pro/broadcast camera you can point to, then, by this definition,
oversamples.  Since, the nature of CCD's is such that a multiplicity of rows
is a requirement for them to function.  We usually speak in terms of how
many "phases" or rows are devoted to managing an area that will,
effectively, become a pixel.  A three phase design is pretty common.  In
aerospace (satellites, spacecraft) and scientific imaging you can find
upwards of 12 phases per pixel.  The phases are excited caterpillar-style to
coerce the collected charge out of the chip.

What's remarcable about the Viper is that they took a chance and introduced
a modificatino to a video camera that, effectively, makes it much more than
it's previous incarnation.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Martin Euredjian
eCinema Systems, Inc.
voice: 661-305-9320
fax: 661-775-4876
martin at ecinemasys.com
ecinema at ieee.org
www.ecinemasys.com















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