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Computer Graphics in Java CR325
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What is Computer Graphics? A kind of Data processing Voice and Signal Processing = 1D data processing Image Processing = 2D data processing Computer Graphics = 3D data in with 2D data out. Geometry is transformed into images.
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What is Computer Animation? Like Computer Graphics with a difference. Animation=movement. This is simulated with image sequences. Output is an image sequence. Input is 3D geometry.
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Why study Computer Graphics? Entertainment Visualization of data (analysis) Simulation can be visualized with CG. CAD (Computer Aided Design)
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What do people study in CG? How to do 2D drawing –How to draw a line –How to draw a circle, etc. How to do 3D drawing –How to draw a 3D line –How to draw a sphere, etc.
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Where do we get input? Pick device –Gives us a location –Mouse, light-pen, arrow-keys, keyboard, –Joystick, tablet, scanner, image –video camera with a cooperative target. –Geometries –Dynamics, kinematics (math).
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Introduction to 2D Graphics Draw some 2D geometries. Input is 2D geometry Ouput is image.
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How do we represent an image? Image Processing answer: 2D array of pixels Computer Answer: BREP:vectors to the right is a bitmap vector vs. bitmap
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What is an image? A 2D array of PIXELS.
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What is a PIXEL A picture element. Typically a pixel can be described as an intensity for light at a given location. –Location (200,20), I = 255; // gray scale –Location (34,50), R=255, G= 0, B =0; //red pixel. Looks like a dot!
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What is an Image? a 2D array of pixels a pixel is a scalar quantity that represents the intensity of light. It smallest area within the given image.
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How do we represent a pixel? how do we represent light?
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Trading an eye for an ear
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Spectra of the Human Visual System ranges from 400 nm wavelength to about 800 nm, 1 nm = 10 ** -9 meters d = rate * time rate = c = 3 * 10 ** 8 meters / second d = wavelength = 400 * 10 **-9 meters T = lambda/c, f = 1/T = c / lambda f = 3 * 10 ^ 8 / 4 * 10 ^ -7 =750.*10^12?
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An eye is a Multi-mega pixel camera It has a lens (adjustable zoom) It has an automatic f-stop (iris 2-8 mm) It has a sensor plane (100 million pixels) The sensor has a transfer function senstive to mesopic range; 380 to about 700 nm
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The eyes have a USB2 data rate! 250,000 neurons in the optic nerve variable voltage output on EACH nerve 17.5 million neural samples per second 12.8 bits per sample 224 Mbps, per eye (a 1/2 G bps system!). Compression using lateral inhibition between the retinal neurons
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Response curves Eye has Gaussian response to light. Gives rise to biologically motivated image processing
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Quantization of an Image Computers use digital cameras -> quantization
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Quantization Error is visible
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Displays Color Monitors are made for people physiological arguments are used for display design
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What is light? any electromagnetic energy visible light is typically visible to the human visual system (eye).
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How do we represent a pixel assume that the pixel is for humans. You need to know the dynamic range of the eye! 1 part in a million is needed for a pixel that displays on a monitor for people. Typically we use 24 bits per pixel, 8 bits per color.
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peter packed a pickled pixel its color was that of hash. And every system that displayed it would crash!
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Displays are designed for human visual system (eye) Painting with LIGHT (additive synthesis) display This is not painting with MUD! (subtractive synthesis) printer
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Overview public int filterRGB (int rgb) { int r = (rgb & 0xff0000) >>16; int g = (rgb & 0xff00) >> 8; int b = rgb & 0xff; int gr = (r + g + b) / 3; int p = 0xff000000 | (gr << 16) | (gr << 8) | gr; return p // p = 0xffgrgrgr;
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How would do you pack RGB? int pack(int r, int g, int b) { return 0xff000000 | (r << 16) | (g << 8) | b; }
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How do I represent the following in decimal int I = 1; int k = ~I+1; how much is k? Ans: -1
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Intro to bitwise ops and - & - bitwise (not && is logical) or - | - bitwise (not || is logical) not - ~ - bitwise (not !, is logical) xor - ^ - bitwise (has no logical correspondence)
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Intro to ANDing int I = 0; int j = 1; I&I is 0 I&J is 0 J&I is 0 J&J is 1
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Intro to Oring int i=0xF0; S={0,1,2,3,4,5,6,7,8,9,a,b,c,d,e,f} int j =0x0F; i|I is 240 = 0xF0 i|j is 255 in decimal = 0xFF 0xF0 = (in base 2) 11110000 0x0F = (in base 2) 00001111 0x0F | 0xF0 = 11111111
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Using hex for ANDing int i=0x7a; int j =0x0F; how much is i&j ? 01111100 & 00001111 = 00001100 = 0x0c
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using hex for not int i=0x7a; int j =0x0F; how much is ~j? 0xfffffff0 nibble is 4 bits, byte is 8 bits
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using hex for xor int i=0x7a; int j =0x0F; how much is i^j? 01111100 = I^ 00001111 = j 01110011 = i^j = 0x73
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Common Radicies in java, you can use: binary (base 2) Radix 2 octal (base 8) Radix 8 decimal (base 10) Radix 10 hexidecimal (base 16) Radix 16
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How come they call it base 2? You can only have 0 and 1, so why call it base 2? Why not call it base 1? Cardinality of the set of symbols is the radix S = {0, 1}, card(s)=2
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Why call it a base? The base of the exponent! 1101, base 2 is, in decimal 1*2^3 + 1 * 2^2 + 0 * 2 ^ 1 + 1 = 8 + 4 + 0 + 1 = 13 base 10. This is called positional notation.
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Doing the positional notation in hex 0x28 = 2 * 16 ^ 1 + 8 * 16 ^ 0 = 2 * 16 + 8 = 32 + 8 = 40 base 10
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