CPSC 461: Copyright (C) 2003 Katrin Becker Last Modified May 25, 2003 10:20 PM
FILE FORMATS
Scientific & Graphics Formats

Main Data File Format Types:

Documents (text; word-processor; LaTex; postscript; etc.)
Electronic Data Interchange (EDI : formats for e-commerce)
Scientific
Graphics (raster; vector)
Audio (sound & voice)
Animation (moving pictures)
Multimedia (video; combined)

GRAPHICS: "Pictures"
2 main classes of sources:

1. Computer generated
2. Natural source ("photos")

| (computer generated) CG | natural source
| cartoon-like | photographic
| fewer colours (256?) | Many colours (24-bit)
| largish patches of identical colour | very few regions of identical colour
| easier to compress | achieving high compression is trickier
uses | cartoons; icons; backgrounds | photographs

2 main kinds of image files:

1. Raster (bitmap) describes pixels - it's actually a PixelMap
2. Vector ("OO") describes lines and shapes

| Raster | Vector
typical application programs used to create | paint programs | draw programs
representation | pixel values | line segments
scalability | awkward | easy to scale without loss of information
device dependence | moderate | high
processing speed (for display) | fast | slow(ish) - must be computed
effects such as smoothing; distortion; sharpening; edgeing; etc. | straight-forward | challenging
"tweening" for animation | pains-taking | straight-forward
uses: | scientific data; pictures; www display; animation | mapping; CAD-CAM; architectural drawing; some animation

Examples: (Which is which?) GIF, JPEG, Encapsulated PostScript, BMP, WMF, PNG, PNM
What goes into a raster file? (Stored Image Format)

2-D Array of Values: 1 for each pixel (uncompressed)
- could be: 1 bit (black and white)
- 8 bits: grey-level or 256-colours
- 24 bits (3X 8 bits):

- Intensities of RGB
- Lookup table values for RGB

- 24 bits : lookup table into triples
- Index to some other data structure used to represent a colour
- Several spectral samples for each colour (eg. high frequencies => edges; rapid change in intensity)

There are many ways to organize these sets of values.

(c) 1981-2002 The Computer Language Company Inc. All rights reserved. Ver. 15.1, 1st Quarter 2002 Computer Desktop Encyclopedia, Alan Freedman
A Monochrome Bitmap The left half of this diagram shows the bits in the bitmap, and the right half depicts what would show on screen. In monochrome systems, one bit is used to represent one pixel. Images that are scanned into the computer are turned into bitmaps, and bitmaps can be created in a paint program.

What goes into a vector file?

- Specified through primitives: lines; circles; text strings; 2D objects; could be 3D objects; colours (and their attributes)
- Colour information (colour maps)
- since most display devices are in fact raster devices (exception: plotters), these will have to be transformed into pixel values before they can be displayed.

There are also many ways to organize these sets of values.

(c) 1981-2002 The Computer Language Company Inc. All rights reserved. Ver. 15.1, 1st Quarter 2002 Computer Desktop Encyclopedia, Alan Freedman
Drawing Vs. Painting Although more painting tools are added to drawing programs and more drawing tools are added to paint programs, their inherent structure is different. Drawing programs (vector graphics) allow for the creation of objects that can be manipulated independently. Paint programs (bitmapped graphics) provide a canvas that can be covered with electronic paint.

SCIENTIFIC:
- often images of a sort, bitmaps
- also need annotations and data organization info
- need detailed info about the data set
- usually some sort of reading of something
- need to know who, what, when, where, why, with what, .....
Examples:

BUFR (Binary Universal Format)
GRIB (Gridded Binary Format) - meteorological data
CDF (Common Data Format) - NASA
DLS - Digital Log Interchange Standard / RP66 (Recommended Practise 66) - well log data

Schlumberger (started American Petrolium Institute)

FITS ( Flexible Image Transport System) - astronomical data
PDS (Planetary Data System) NASA
PLOT 3D - fluid dynamics - NASA
SEG (Society of Exploration Geophysists) - 5 types

- goals & needs are different - some overlap | Scientific | Graphics
Most Important Aspect | numbers (values rather than appearance) | pictures
Compression | Lossless ONLY (The astronomers wouldn't like it much if we lost stars) | Lossy might be acceptable

CPSC 461: Copyright (C) 2003 Katrin Becker Last Modified May 25, 2003 10:20 PM