Removal of Object Image Edge Darkening (Vignetting)
through Adaptive Contrast Adjustment of a Linear Light
Source
Abstract
One of the
problems encountered in transferring objects to a digitized medium with a
linear scanning system is image edge darkening (vignetting). Edge darkening
arises from the decrease of refraction or collection property of the lens group
towards their ends as the light reflected on the object is projected onto the
surface of CCD sensor. In general, lens, due to its optical structure, forms a
light distribution like a downward parabolic decreasing from its center towards
the ends under the homogeneous light source.
Calibration of
lens groups usually becomes insufficient at removing darkenings formed on the
image of an object under the homogenous light distribution. For this purpose, realization
of microcontroller-based adjustment of independent and dynamic contrast for
each LED of the linear light source designed in LED array is considered. The sample
values taken from LED array of the light source
prior to image capture of the scanner is compared with white reference
LED array values so that it is made a decision on the distribution of light on
the object. The individual dynamic contrasts of LED array are adjusted by
driving a PWM-based switching circuit with the brightness values obtained from
the computer.
The image results obtained by applying the known effective shadow
correction algorithms to the images under the homogeneous light source is
compared with the image results reported in eliminating edge darkening.
Android Based
Telemetry Application
Abstract
This study which covers a telemetry application using GSM technology has
already accomplished using TC65 GPRS modem which supports java programming
language. The application hardware, called redressor unit and commonly used in
cathodic protection, consists of three main parts: AC to DC converter unit, remote
measurement and control unit (RMCU), and a server computer. A
microcontroller-based measurement unit, managed by the server application,
measures the output voltage and current of the converter and sends them back to
the server through the modem. The server has a database which stores the data
and sends reference output voltage of redressor if it is required.
A new study will be started using a new GSM/GPRS device instead of TC65.
The mobile device which supports the android operating system will have a
dynamic IP and run as the client application and set the communication between
the server and RMCU.
