Browse Prior Art Database

Automatic Exposure Metering by Differential Vector Quantization

IP.com Disclosure Number: IPCOM000101554D
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 97K

Publishing Venue

IBM

Related People

Chang, PC: AUTHOR

Abstract

This article presents an automatic exposure metering scheme based on the vector quantization technique which provides accurate exposures for various bad lighting conditions.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Automatic Exposure Metering by Differential Vector Quantization

       This article presents an automatic exposure metering
scheme based on the vector quantization technique which provides
accurate exposures for various bad lighting conditions.

      Most modern cameras are equipped with an automatic exposure
system, e.g., averaging-type, center-weighted, zone metering, and
spot metering.  Each exposure system is designed for moderate
lighting conditions as well as some special conditions.
Unfortunately, none of them is consistently better than others in
various situations.  A user has to adjust the exposure manually in
such awkward situations as back light, high contrast, interior, or
otherwise difficult lighting.  The exposure compensation totally
relies on the experience which is expensive to obtain in terms of the
time and the money.  Even professional photographers often make
exposure mistakes in difficult lighting conditions.

      In recent years, several camera manufacturers started to
introduce more advanced exposure systems which collect the light
intensity from several zones and then run certain proprietary
algorithms to decide the optimum exposure.  This disclosure
introduces a differential vector quantization (VQ), also called
separate mean VQ or mean/shape VQ [1], based exposure metering system
which is robust to different bad lighting situations.

      The figure shows the proposed system.  It divides the whole
view area into k zones and places a photo sensor corresponding to
each area.  A vector X is formed which represents the light intensity
in each zone.  The average exposure X0 which is detected by another
photo sensor covering the whole area is sent to the differential VQ
together with the vector X.  Basically, the average exposure is used
as the preliminary and the main control signal.  The output from the
VQ is only used as the exposure compensation (Ec).  The difference
vector X - X0 is used as the input to a VQ encoder which finds
the best matched pattern in the sense of minimizing the distortion
between the input pattern and the codeword.  Associated with each
codeword, an exposure compensation predetermined by photo experts and
the VQ design process is stored in the exposure table.  Once a
codeword is chosen, its index is used...