Browse Prior Art Database

CCD Imaging Device With Center Weighted Area Averaging

IP.com Disclosure Number: IPCOM000122494D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 4 page(s) / 161K

Publishing Venue

IBM

Related People

Schlig, ES: AUTHOR [+2]

Abstract

A charge coupled optical imaging device is disclosed which generates (along with the pel signals) area averages over blocks of pel values, one average centered on each pel. The weights given to the values of pels in each block are approximately gaussian; the closest to the center of each region receive the greatest weight in the average. The size of the region is not fixed but may be determined by the pattern of clock pulses applied to the device, and consequently may be programmed by the user to give the best results with the image at hand. When applied to area imaging arrays, the complexity and cost of the disclosed device are little more than those of an imager without averaging.

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CCD Imaging Device With Center Weighted Area Averaging

      A charge coupled optical imaging device is disclosed
which generates (along with the pel signals) area averages over
blocks of pel values, one average centered on each pel.  The weights
given to the values of pels in each block are approximately gaussian;
the closest to the center of each region receive the greatest weight
in the average.  The size of the region is not fixed but may be
determined by the pattern of clock pulses applied to the device, and
consequently may be programmed by the user to give the best results
with the image at hand.  When applied to area imaging arrays, the
complexity and cost of the disclosed device are little more than
those of an imager without averaging.

      The area averages and pel values may be used for image noise
reduction and to approximate the laplacian of the image, which may be
used for such image processing tasks as edge enhancement and dynamic
thresholding.

      In the following we will assume a 4-phase, N-channel silicon
CCD technology.  The basic building block of the present invention is
a center-weighted linear averager (CWLA); a center-weighted area
averager (CWAA) is formed as a two-dimensional array of CWLAs.  A
schematic layout of a 4-phase CWLA is shown in Fig. 1.  Regions shown
are the CCD channel areas controlled by the indicated clock phase
electrode.  Spaces between regions are channel-stop.

      The operation of the device of Fig. 1 will be explained with
the help of the timing diagram of Fig. 2, for the simplest practical
case of a three-pel linear center-weighted average.  Initially,
assume that a signal charge packet resides at each stage.  These
packets have various amplitudes which represent the image intensity
at corresponding image pels.  The packets are kept isolated from each
other at this time by keeping at least one shift register phase low.
The packets will have reached this position in any of a variety of
ways; being created in situ by imaging; being created by imaging in
photodiodes associated with each stage; being shifted in from a
serial input to the shift register, etc.

      At time T1, the charge at each stage resides at A, B and 1,
which are high while 2, 3 and 4 are low.  A and 1 are designed
to have the same charge capacity, so that when B turns off at T2 half
the charge in each stage is at A and half is at 1.  Phase 2
turns on (high) and phases 1 through 4 go through one 4-phase cycle,
shifting each charge packet half formerly at phase 1 one stage to the
right.  The half at phase A remains stationary.  At T3, phase 2 has
turned off (low) and B turned on, restoring the condition of T1 and
merging the half charge packets at each stage.  B goes low, dividing
the charge as before, the register shifts one stage as before, and
the charge halves are combined as before.  At T4 each stage has the
desired 3-pel linear center- weighted average.  A and then B go low,
co...