QR Barcode Detection

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QR Barcode Detection

• Machine Vision

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Components in QR code readers
QR Code
Image Conversion
Photo
1010111011001111000110010101
Raw Data
QR Detector
QR Decoder
This is what we are focusing on
http//www.yahoo.com
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QR Properties (Basic)
Version Information
Position Patterns - Determines the correct
orientation
Position Patterns may be detected horizontally or
vertically by the unique B-W-B-B-B-W-B ratio
Data bit
Alignment Pattern - Used for perspective
transformations corrections
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QR Detection Algorithm
Proceeds by horizontally column scanning the raw
image pixels (or vertically row scanning) to
locate the 3 position patterns identified by the
1-1-3-1-1 ratio
After a potential position pattern is located, it
is then cross-checked in the other direction
for the same ratio and position pattern size Also
determines the center of the position pattern
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Triangle Point Ordering
Remember Pythagoras' theorem?
B

Points A and C may be in the wrong order so
we can use the cross product to determine the
angle between point B and the line segment AC

C
The points at either end of the hypotenuse are
points A and C

A
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Perspective Corrections
Simply maps points on a known square to points on
the distorted, rotated or skewed square
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Perspective Correction Algorithm

• for (long i 0 i lt dimension i) // y-axis
  direction
• for (long j 0 j lt dimension j) // x-axis
  direction
• // The QR code is read as if it were an
  un-rotated and un-skewed image
• POINT pt
• pt.x (j module_size)
  half_module_size
• pt.y (i module_size)
  half_module_size
• POINT p transform.TransformPoint(pt) //
  Does the perspective correcting
• qr_store.set(pt, image.IS_BLACK(p))

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Perspective Corrections
and rotation corrections for free (with no use of
expensive trigonometry functions)
size bit size x dimension


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1
Only version gt 1 has the alignment pattern
size bit size x dimension
4


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This is why locating 4 points is so important
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Results

• lt 1000 Source Lines of Code (SLOC)
• Almost no floating-point code
• Working to make it none
• Very quick

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Results
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Future Work

• Image filtering and cleaning
• Histogram analysis
• Colour to greyscale to monochrome
• QR decoding
• Extracting the contents (Message, URI etc)
• ReedSolomon error correction
• Level L
• Level M
• Level Q
• Level H