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Introduction
• Purpose of the device
• A brief introduction to the Braille system
• Scanner operation
• The Prototype
• Image capture & processing
• Proposed improvements
• Conclusion
Why?
• Primarily for non Braille users– Education– Workplace
• Reproduction of worn or old Braille
• Electronic storage of Braille texts
The Braille System
• Tactile medium consisting of 6 “dots”
• Context sensitive– people = p– wh = : or which or : (colon)– Includes many rules for use
• Similar to shorthand
• May be printed both sides - interpoint
Scanner Operation
• Hand held portable unit
• Camera assembly is moved over the Braille line
• Operates in real time
• Results of the scan are displayed on the host computer
CCD Operation
• 10ms integration time
• Pixels clocked out in 2.6ms
• 100 µs per sample
• Allows 7ms per slice processing time– (context switching and overheads considered)
Linear Motion Detection
• Slotted disk and IR detector/emitter
• Gear system to produce pulses at 200DPI
• Each pulse sends an interrupt to the DSP
Prototype Development Platform
• TMS320C50 DSP by Texas Instruments– Low cost– 10K words of data/program memory– Incorporates Analog Interface Circuit (AIC)
• TLC32040
• Programmable
• Include anti-aliasing bandpass filter
– Emulates serial (RS232) communications
Cell Element DetectionAre dots present?
• 25 samples at 100u second intervals
• Reference levels are averaged
• Samples are compared to reference level
• Results are written to scan word
Cell Compilation
• Scan words are captured at 200 dots/inch
• Stored as a single word, position oriented– 10 = bright– 01 = shadow– 00 = reference level– 11 = status
• dots are 1mm diameter => 8 scans per dot
Cell Compilation
• 50 samples kept (scan word) in the image buffer.
• Cells assembled from this image– Image buffer is compared to each possible
“ideal cell” (63 combinations)
Cell Compilation
• When a cell is matched:– Send binary Braille code
• Determined from a lookup table
– Clear the image buffer– Host processor “expands” grade 2 code
• Text is now available for display or storage
Grade 2 Decomposition• Algorithm by Paul Blenkhorn
• A simple state machine
• Allows for exceptions
• Uses look up tables and therefore allows :– Foreign language support– Special purpose codes e.g.
• Music
• Math
• Implemented in C
Proposed Improvements
• Quadrature motion detector will allow:– Reversal of scan direction– Decreased resolution
• Implement Fuzzy “dot” detection
• Use the SI pulse for triggering illumination
• Improve ergonomics
Conclusion
• Achieved– Image capture of a tactile medium– Dot recognition (position)– Grade 2 Braille decode– OCR of embossed Braille
Conclusion (continued)
• Further development should yield a useful device that overcomes the communication barrier between Braille users and the mainstream community.
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