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24 Cards in this Set
- Front
- Back
Bitmap images |
store images as a list of numbers, one per pixel .bmp |
|
Advantages |
Quality |
|
Disadvantages |
Size |
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Calculating Size of Bitmap |
(W*H*D/8,000,000) |
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Compression |
Lossy and Lossless |
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Lossy |
reduces size by discarding data |
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Advantage |
Large reduction in size vs. lossless |
|
Disadvantage |
Can reduce quality |
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reducing colour depth |
reducing colour depth can cause posterizing |
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avoiding this by using a colour palette |
indexing colour: only stores most common colours in image index included at start of file |
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chrome sub sampling (lossy) |
120 million rod cells sense luminance (brightness) 6 million cones sense chromo (colour) |
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Subsampling |
store Y(luminance) R-Y |
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Luminance |
Y=R+G+B R=(R-Y)+Y G=Y-R-B |
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Subsampling to compress |
break image into 2x2 blocks store luminance for each pixel average |
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JPEG |
Joint Photographic Experts Groups uses Chroma Subsampling |
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compression artefacts |
sub sampling causes articling round sharp edges, photos look ok; logos and diagrams can look poor though |
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lossless |
reduces size without discarding data ; less effective than lossy at reducing file size |
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Run Length Encoding |
reduces file size by removing runs of repeated data |
|
WWWWWBBBWWWWWBWWWWWWWWW |
5W3B5W1B9W |
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Supported file formats that use lossless |
TIFF (Tagged Image File Format) < uses RLE PNG (Portable Network Graphics) GIF ( Graphics Interchange Format) |
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Vector Images |
Geometrical Primitives: Points, Lines, Curves and Polygons |
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Rendering |
Vector images must be rendered or rasterized at display time which is computationally expensive |
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scaling |
they can be scaled to any size without any loss of quality and are often far smaller than their bitmap equivalent |
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common uses |
drawing charts and graphs fonts .svg is part of html5 |