Digitization

1
Digitization

• Scanning
• Vectorization
• OCR
• On-screen digitization
• Digitization with a tablet or table

2
Specifications for scanners

• Size of original (width, A4, ..), type of
  original
• B/W, grayscale or color
• Speed (cm/s)
• Resolution (DPI, dots per inch)
• Connectivity (Parallel port, SCSI, USB ... Driver
  software)
• Included software
• Output formats
• Price

3
TWAIN and SANE

• www.twain.org
• An API for Windows and Mac
• A program running in the host computer makes
  requests (get image, delete image, ...) to the
  peripheral
• SANE is for Linux
• saned allows network access to the scanner which
  is connected to a Linux machine

4
Vectorization

• Convert to curves
• Manual (find points)
• Automatic
• Depends on the original

5
OCR

• Optical character recognition
• Scanned text ? text

6
Digitization tablet or table

• Specifications
• Size of the work area
• Connectivity
• Compatible software

7
Essential CG (raster images)
8
Raster formats

• Proprietory / Open
• is specification published?
• may have been reverse-engineered
• Standard?
• W3C, ISO, ...
• Patent issue
• Support in programs
• Georeferencing (metadata)

9
Colors or no colors

• Black and white
• 1 bit per pixel
• Grayscale
• for example one byte (8 bits) per pixel
• Color
• for example 3 bytes per pixel (Red Green Blue)
• Color palette
• for example one byte per pixel
• pixel value is an index to the color palette
• changing of palette is fast

10
Compression

• Why?
• data redundancy
• Simple Run Length Encoding (RLE)
• Others ZIP, LZW, Wavelets
• Lossiness (JPEG)

Suppose the following string of data (17 bytes)
has to be compressed ABBBBBBBBBCDEEEEF Using RLE
compression, the compressed file takes up 10
bytes and could look like this A 8B C D 4E F
11
Rectification

• On-screen digitization of known points
• xf(x,y)
• yf(x,y)
• decide on the target raster
• go through the target raster pixel by pixel and
  look from the original image what to put in them

12
Image viewing and manipulation
13
Methods on viewport

• Zoom
• enlarge, shrink (zoom in, zoom out) within
  current viewport
• Pan
• move the image with respect to the current
  viewport

14
Image methods

• Crop
• select a (rectangular) part of the image and cut
  the rest off
• Scale
• enlarge or shrink the image (maybe saving the
  aspect ratio)
• Rotate
• Transformations
• based on control points

15
Image manipulation

• Thresholding
• Adjusting contrast
• Adjusting sharpness
• Filtering
• Inversion
• Posterizing