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Digital Multimedia - Coggle Diagram
Digital Multimedia
Bitmapped Image
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Compression
image files may be too big for network transmission, even at low resolution
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Lossless compression
always possible to decompress compressed data and obtain an exact copy of the original uncompressed data
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JPEG compression
lossy technique, well suited to photographs image with fine detail and continuous tones
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JPEG - Encoding
after quantization, there will be many 0 coefficients
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JPEG - Decompression
expand runs of zeros and decompress Huffman-encoded coefficients to reconstruct array of frequency coefficients
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Compression Artefacts
if use low quality setting, boundaries btw 8x8 blocks become visible
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Masks
area not selected is protected, as if masked by stencil
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Blurring
low frequency filter
3x3 convolution mask coefficients all = to -1, exept centre = 9
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unsharp masking
copy image, apply gaussian blur to copy, subtract it from original
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Vector Graphic
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attractive for networked multimedia, but nor widely used on WWW
Coordinates
rectangular array of pixels, each pixel may be identified by row and column numbers (r,c)
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Rendering
represent lines, curves, shapes, by parameter of their defining equation
e.g line y = mx + c, store m and c
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Anti-aliasing
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how to overcome jaggies
mitigate effect by coloring pixels in shades of grey, brightness varies according to extent of intersection with an idealized 1 pixel wide line
Shapes
drawing programs and vector graphics lang provide basic repertoire of shapes - easily be represented mathematically
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straight lines, polylines & polygons
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Path
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if 2 curves joint at a point in such a way - direction lines through that point from a single line extending the same distance in both direction, the join will be smooth
pen tool in drawing programs lets you build up curves in this way by dragging at successive anchor points
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3D rendering
start with mathematical model of objects in 3D space, need a 2D picture
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hidden surface removal
non-trivial, but well understood
can colour surfaces arbitrarily, sufficient for removing visual ambiguity of wire frame
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