1	Graphics File Format and Data Compression Techniques (take 2) Week 8
2	Administrivia (is back) Distribute exams Discuss groundrules Please sign in as you turn exams in
3	Halloween Hope I didn’t spoil your Halloween Have some candy…
4	Tonight Exams due by 7:30 Break until 8:00 Brief 1hr lecture
5	Exam Closed book, no computers or calculators Please follow instructions carefully Show all work Don’t know an answer? Show me what you do know… (give me something to work with) Sign attendance as you turn exam in
6	Eye Evolution this week in Journal Science Ciliary photoreceptors with vertebrate-type opsins in an invertebrate brain Platynereis dumerilii 'living fossil,‘ (a marine worm) light sensitive Opsin molecule Same as the human/vertibrate Opsin Indicates a common evolutionary ancestor
7	PNG filters PNG compresses lossless data better than GIF In part because a series of lossless (reversible) filters are used Filters examine pixels from rows and columns already traversed Assumes that deltas take less room to store than the pixel values
8	PNG filtered pixels
9	PNG filters 0 Unfiltered 1 Sub filtered (diff from pixel on left) 2 Up filter (diff from pixel above) 3 Avg filter (diff from avg pixels to left and above) 4 Paeth filter (diff from value predicted by neighbors)
10	Paeth predictive filter horiz = abs(above – upperLeft); vert = abs(left – upperLeft); diag = abs(left + above – 2* upperLeft); if (horiz <= vert && horiz <= diag) return left; if (vert <= diag) return above; return upperLeft;
11	Audio Delta Coding Similar but 1 dimensional predictive filter Used for lossless audio compression Delta techniques assume small changes between samples
12	Example 4 seconds of EEG data Example from P. Bourke
13	Intrasample diff. distribution Few bits needed to encode (most) diffs
14	Lossless Audio Pretty much: Predictive filtering Entropy coding Extra media specific tricks: Stereo Decorrelation
15	Predictive Filtering Any predictor function may create a filter When encoding: residual = sample – predictor(lastSample) When decoding: sample = residual + predictor(lastSample)
16	Predictive Filtering In a delta filter (simplest): prediction = lastSample More complicated filters: Dynamically change weighting to adapt the correlation between lastSample and prediction Prediction=lastSample*weight
17	Stereo Decorrelation Signals in a stereo mix are usually very similar Convert L+R signals to X+Y: X=L-R Y=R+(X/2) This could be accounted for in a special filter…
18	CAD Computer aided design Lossless is critical! CAD: isn’t about pixels is precisely describing the relationships of objects Stores vector info not pixels
19	CAD & SGI We sold many ‘seats’ to CAD Custom stripped down configurations CAD is very price sensitive Much low end CAD on PC with AutoCAD Airplanes designed on CATIA on SGI
20	DXF: AutoCAD export format Stores floating point values: Primary X,Y,Z coordinate Entity's thickness
21	CAD entities Primitives: LINE, POINT, CIRCLE, ARC, SOLID, 3DLINE, 3DFACE, SHAPE, TEXT, POLYLINE, etc. Library of objects are built out of these primatives
22	Modeling Contrast Game modeling CAD modeling
23	Resource Libraries No longer unusual to construct physical object out of game/animation models