image composition and compression
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Digital Art
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Image files are composed in 2 ways: Raster (pixel) Vector (geometric) data
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Mostly used in Photoshop
Composes images by a grid (columns and rows)
Each pixel consists of numbers representingmagnitudes of brightness and colour
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More pixels = Higher resolution; clearer imagesformed
Less pixels = Lower resolution; blurrier imagesformed
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Mostly used in Illustrator
Uses geometrical primitives such as points, lines,curves, and shapes or polygons to form
mathematical equations
Represent images in computer graphics
Keeps resolution the same even when scaled
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Geographic location of each cell is implied by itsposition in the cell matrix
Other than an origin point, no geographiccoordinates are stored
Therefore, data analysis is usually easy to programand quick to perform
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Ideally suited for mathematical modeling andquantitative analysis
Discrete data is accommodated equally well ascontinuous data facilitates the integrating of thetwo data types
Grid-cell systems are very compatible with raster-based output devices
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Cell size determines resolution at which data isrepresented
Difficult to represent linear features depending onthe cell resolution; network linkages are difficult toestablish
Since most input data is in vector form, data mustundergo vector-to-raster conversion
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May lead to generalisation and choice ofinappropriate cell size
Most raster output maps do not need high clarity
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Data can keep its original resolution and formwithout generalisation No pixelated imagesformed
Graphic output is usually more aestheticallypleasing
No data conversion needed as most data are invector (e.g. Hard copy maps)
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Accurate geographic location of data ismaintained
Allows for efficient encoding of topology
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Location of each vertex needs to be storedexplicitly; leads to large data size
For effective analysis, vector data must beconverted into a topological structure
Requires extensive data cleaning after conversion
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Topology is static; any updating of data requires re-building of the topology
Algorithms for manipulative and analysis functionsare complex; lead to intensive processing
Limits functionality for large data sets (e.g. a largenumber of features)
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Continuous data is not effectively represented invector form
Spatial analysis and filtering within polygons isimpossible
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Uses algorithms to decrease size file
2 types of image file compression algorithms: Loseless Lossy
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Reduces file size without losing image quality
Unable to compress a file as small as lossycompression file
Chosen when image quality is valued above filesize
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Takes advantage of the inherent limitations of thehuman eye and discards invisible information
Allows variable quality levels (compression)
Compression levels increased = File size reduced
At high levels of compression, image deteriorationbecomes noticeable
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The detail that an image holds
Applies equally to digital images, film images, andother types of images
Higher resolution = More image detail
Resolution can be measured by how close linescan be to each other and still be seen
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Resolution units can be measured by physical sizes(e.g. lines per mm, lines per cm, etc.)
Line pairs are often used instead of lines
A line pair is a pair of adjacent dark and light lineswhile lines counts both dark lines and light lines
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A resolution of 10 lines per mm means 5 dark linesalternating with 5 light lines, or 5 line pairs per mm
Photographic lens and film resolution are mostoften quoted in line pairs per mm
TV lines refer to lines per picture height
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There are many types of resolutions but you will onlylearn about the two common ones
They are: Pixel resolution Temporal resolution
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An image of N pixels high by M pixels wide canhave any resolution less than N lines per N TV lines
The format for resolution is to describe the width bythe height of the overall image; e.g. 640 by 480
Another way to describe the resolution is to givethe number of megapixels
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It is calculated by width X height and 1 million
These resolution are not accurate as they just serveas an order on image resolution
Pixel columns means width
Pixel rows means height
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Movie cameras and high-speed cameras canresolve events at different points in time
The time resolution used for movies is usually 15 to30 fps
High-speed cameras may resolve 100 to 1000 fps,or even more
Many cameras and displays offset the colorcomponents relative to each other or mix uptemporal with spatial resolution:
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Many cameras and displays offset the colorcomponents relative to each other or mix uptemporal with spatial resolution:
Digital camera(Bayer color
filter array)
LCD (Triangularpixel geometry)
CRT (shadow mask)
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There are three main colour-encoding systems: PAL (Phase Alternating Line) NTSC (National Television System Committee) SECAM (Squentiel couleur mmoire, French
for "Sequential Color with Memory)
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Analog
350240 (260 lines): Video CD 330576 (250 lines): Umatic, Betamax, VHS,
Video8
400576 (300 lines): Super Betamax, Betacam(pro)
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Analog
440576 (330 lines): analog broadcast 560576 (420 lines): LaserDisc, Super VHS, Hi8
670
576 (500 lines): Enhanced DefinitionBetamax
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Digital:
720576 (520 lines): D-VHS, DVD, miniDV, Digital8,Digital Betacam (pro)
720576 (400 lines): Widescreen DVD(anamorphic)
1280720 (720 lines): D-VHS, HD DVD, Blu-ray,HDV (miniDV)
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Digital:
14401080 (810 lines): HDV (miniDV) 19201080 (1080 lines): D-VHS, HD DVD, Blu-ray,
HDCAM SR (pro)
10,0007000 (7000 lines): IMAX, IMAX HD,OMNIMAX