DETECTION AND HEALING OF STREAKS CAUSED BY DUST IN SHEETFED SCANNERS; MOTOR CONTROL, MODEL BASED HALFTONING, AND PRINT MASK DESIGN USING DIRECT BINARY SEARCH FOR INKJET PRINTERS
In this thesis, I present three research topics in the areas of scanning and printing.
The first topic is on detecting and removing specific artifacts in images scanned using
sheetfed scanners. Sheetfed scanners are widely used for scanning stacks of loose pages at
high speed. The scanhead in the sheet-fed scanners is stationary and the pages are fed with
an automatic document feeder. When dust particles get stuck onto the scanner glass, they
reflect the incident light and cause vertical streaks in the scanned images. These artifacts are
known as dust streaks. I have developed a method for detecting and healing dust streaks.
The second topic is on motor control system and test page design for inkjet printers.
Motor control consists of two main parts which are movement of the printhead in the scan
direction and the process direction. Scan direction movement needs to have a constant
smooth velocity in order to avoid banding artifacts. Process direction movement needs to
advance an exact distance in order to avoid misalignment. The full procedure for implementing
the motor control on a microcontroller, determining optimal parameters, and designing
test pages for validating the motor control system is presented.
The third topic is on printer model based halftoning and print mask design using DBS.
Inkjet printers can fire nozzles at specific pixel locations. Due to nozzle clogging and nonuniformity
in the nozzles, inkjet printers usually print in the multipass mode to reduce print
artifacts. In this mode, the printhead goes over the same line more than once with different
sets of nozzles of the same ink. Print mask determines which pixels are printed at a certain
pass and which pixels are not printed. I developed a printer model to predict prints and
also developed test pages to obtain parameters for the printer model. Then, we looked into
model based halftoning and print mask design using the direct binary search algorithm. In
addition, I investigated the advantages and disadvantages of using light magenta as opposed
to using black ink in 4-color printing.