curve encoded compression and transmissioncurve encoded compression and transmission (cecat)...
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Curve Encoded Compression and Transmission
Sending Document Images to Low-Bandwidth Users
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Document ImagesDigital Libraries
• Wide Distribution• Easy Access• Less “Shelf” Storage
Digital Media• Text Transcripts• Document Images
Genealogical Document Images• Handwriting (no OCR)• Mostly Bi-tonal (but needs grayscale)• “Browsing” Operations
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Challenges
How do we give researchers the ability to browse through family history document images quickly despite “low bandwidth” connection speeds?
Slow Connection Speeds
Large File Sizes
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Approach One: Image Compression
Transform• JPEG• Wavelet
Context• GIF• CCITT-G4
Codebook• JBIG2• JB2
“Hybrid” Strategies• DjVu (Bottou et al. ‘98)
• SLIm (http://research.microsoft.com/dpu/)
• DigiPaper (Huttenlocher et al. ’00)
Foreground MaskBackground Image
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Approach Two: Progressive TransferContent Progressive
Example: DjVu (Bottou et al. ‘98) Quality ProgressiveExample: JITB (Kennard ’03)
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Curve Encoded Compression and Transmission (CECAT)
Compression1) Extract Foreground Mask from Image2) Detect and Mark the Contours3) Encode Contours as 1st – 3rd Order Bezier Curves4) Group Curves by Locality & Priority
Transmission1) Transfer & Fill Most Important Contours2) Transfer Rest of Foreground3) Add Grayscale Variations to Foreground4) Transfer Background Color Image
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Preprocessing: From Image to Contours
4) Contour Detection (Witten et al. ’94)
1) Convert to Grayscale
2) Apply Median Filter (Hutchison ’04)
3) Thresholding Operation (Niblack ’85)
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Finding a Parametric Fit to Contours
228 Lines = (max 912 bytes)122 Quadratics (max 732 bytes)
Curve Order Bezier Curve Parametric Representation File Size
1st (Line) p(u) = (1-u)p0 + up1 4 bytes
2nd (Quadratic) p(u) = (1-u)2 p0 + 2u(1-u)p1 + u2 p2 6 bytes
3rd (Cubic) p(u) = (1-u)3 p0 + 3u(1-u)2 p1 + 3u2(1-u)p2 + u3 p3 8 bytes
p(u) = points on the curve (u Є [0, 1]) pn = Bezier control points
Results Using Least-Squares-Best-Fit Algorithm
77 Quadratics & 59 Lines (max 698 bytes)
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Lossy Compression: Error Tolerance
Error Metric: Maximum Pixel Distance Between Points on the Contour and the Parametric Curve
0.51.02.04.08.016.0
16.0
8.0
4.0
2.0
1.0
0.5
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Progressive Transfer: Foreground
Transfer Strategy: Send (and Fill) the Most Important Sets of Contours First
Encoding Strategy: Sort Parametric Curves According to Locality and/or Priority
Demonstration
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Progressive Transfer: Background
1) Foreground Mask Complete
2) Foreground Grayscale Data
3) Background Color Image
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ReferencesDjVu
– http://www.djvuzone.org/home.html
DigiPaper– http://www.dlib.org/dlib/january00/moll/01moll.html
Contour Following– Ian H. Witten et al. Managing Gigabytes. Van Nostrand Reinhold: New York. 1994
Niblack Thresholding– Wayne Niblack. An Introduction to Digital Image Processing. Prentice-Hall
International, 1985.
Just-In-Time-Browsing– Douglas J. Kennard. Just-In-Time Browsing for Digital Images. Thesis Presented to
BYU: February 2003
Quadratic Contour Compression– Michael D. Smith. Handwriting Compression using Quadratic Curves. BYU CS 750
Project Write-Up. November 29, 2003
Median Filter Background Removal– Luke A. D. Hutchison et al. Fast Registration of Tabular Document Images Using
Fourier-Mellin Transform. In Proceedings of DIAL04, pages 253-269, January 2004.