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MultimediaBeta-version

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Overview -1

Required backgroundC , C++ or JavaCS240 (Data Structures) or CS212 (for Engineers)

This is NOT a graphics course (see CS460/560)

Labs Data compressionElements of graphics in OpenGLPhoto manipulation

GIMP Steganography

Creating & Rendering models

Topics (general order of coverage)

Compression Encoding/Decoding Codecs Huffman encoding

example lab! Working with Images

Image creation Photography Drawing RIB (Renderman Interface

Bytestream) Modeling• OpenGL – lab!• Makehuman, 3DCanvas,

etc. lab! Image manipulation

Gimp, Photoshop, etc. lab! Stereoscopic & other 3D Rendering lab!

Bitmaps Ray tracing

Animation Hand drawn Program generated• Stop-motion• 3D CGI• Alice lab!• DirectX & OpenGL

Hardware acceleration RIB revisited Shaders

Steganography lab! Additional topics (time

permitting) Augmented reality Geospatial data systems

Software we might use (all free)

Modelers and environments Ayam – ortho & 3D 3DCanvas – 3D Blender – ortho & 3D Makehuman - 3D

Renderers Aqsis Pixie – no GUI, file input

Compression

Codecs

A device or program for encoding and/or decoding a digital data stream or signal

Encoding A->D for storage or transmission Decoding D->A for playback Lossy vs. lossless Raw uncompressed Pulse Code Modulation

(PCM) audio, a digital representation of an analog signal where the magnitude of the signal is sampled regularly at uniform intervalsE.g.; (44.1 kHz, 16 bit stereo, as represented on an

audio CD or in a .wav or .aiff file) is a standard across multiple platforms.

Codecs - 2

May emphasize aspects of data Video:

motion vs. colorAudio:

latency (cell phones) vs. high-fidelity (music)Data size:

transmission speed or storage size vs. data loss

Codec References

Forensic Computing: A Practitioner's Guide by T. Sammes & B. Jenkinson (Springer, 2000), ISBN: 9781852332990 .

http://www.garykessler.net/library/file_sigs.html

Considerations

Tradeoffs compression speedcompressed data size quality (data loss)

Areas of studyinformation theoryrate-distortion theory

Popular algorithms (all lossless)Lempel-Ziv (LZ)LZW (fast decompression)LZR (LZ-Renau) (ZIP files)LZW (Lempel-Ziv-Welch) (for GIF files)

Lossless Encoding

Huffman compressionBit string representing any symbol is never a

prefix of the bit string representing any other symboli.e.; if 010 is the code for a symbol, then no other symbol starts with 010.

Frequency table must be known, computable or included

Lossless – every character gets encoded Arithmetic encoding

Probabilistic algorithmSlightly superior to Huffman, but often

patented!

Methodology

Compute a model of the datae.g.; a Huffman tree based on probabilityProbability determined from input file

Map the data according to the modelRead 1 symbolSearch the model (tree) for that symbol

If it’s a Huffman tree, going left=0, right=1 Append each 0 or 1 to the code string When symbol is found, you are done Note: all symbols will have < 8 bits (thus

compression)

Sample of prefix coding & compression

B e a r c a t s (8 bytes of text):010101100110001110001111 encoded as123456781234567812345678 3 bytes

A simple Huffman-like code(w/o probability basis) 0 1

C 0001

Compression-Model types

StaticRead all the dataCompute frequenciesRe-read the data & encode

DynamicBuild simple basic modelModify model as more data is processed

Standard Compressed-File Content

Three parts: 24-byte header with magic # (defines codec)variable-length annotation blockcontiguous segment of audio data.

Storage methodologynetwork (big-endian) byte ordermulti-byte audio data may require byte

reversal in order to operate on it by the arithmetic unit of certain processors

Example 1: Header file for .AU files

typedef unsigned long u_32; // unsigned 32-bit integer

typedef struct {

u_32 magic; // the “magic number”

u_32 hdr_size; // byte offset to start of data

u_32 data_size; // length (optional)

u_32 encoding; // data encoding enumeration

u_32 sample_rate; // samples per second

u_32 channels; // # of interleaved channels

} Audio_filehdr;

Following is from: #include <multimedia/libaudio.h>

AUDIO_FILE_MAGIC ((u_32)0x2e736e64) /* “.snd” */

Audio Encoding Enumerations

AUDIO_FILE_ENCODING_MULAW_8 (1) /* 8-bit ISDN u-law */

AUDIO_FILE_ENCODING_LINEAR_8 (2) /* 8-bit linear PCM */

AUDIO_FILE_ENCODING_FLOAT (6) /* 32-bit IEEE floating point */

AUDIO_FILE_ENCODING_DOUBLE (7) /* 64-bit IEEE floating point */

AUDIO_FILE_ENCODING_ADPCM_G721 (23) /* 4-bit CCITT g.721 ADPCM */

AUDIO_FILE_ENCODING_ADPCM_G723_3 (25) /* CCITT g.723 3-bit ADPCM */

AUDIO_FILE_ENCODING_ALAW_8 (27) /* 8-bit ISDN A-law */

“Linear” values are SIGNED int’s.Floats are signed, zero-centered, normalized to ( -1.0 <= x <= 1.0 ).

Example 2: ZIP files (PkWare)Purpose Size in bytes

Signature header 4

Required version 2

GP flags 2

Method 2

Last mod time 2

Last mod date 2

CRC-32 4

Compressed size 4

Uncompressed size 4

Filename length 2

Extra field length 2

File name variable

extra variable

Ref: http://livedocs.adobe.com/flex/3/html/help.html?content=ByteArrays_3.html

More info on encoding

http://www.pkware.com/documents/casestudies/APPNOTE.TXT

http://www.fileinfo.com/filetypes/compressed

Recording Bit-Rate

Constant (CBR)rate at which a codec's output data should be

consumed is constantMax bit-rate matters, not the averageUses all available bandwidthNot good for storage (lossy)

Variable (VBR)Quantity of data/time unit (for output) variesBetter quality for audio and videoSlower to encodeSupported by most portable devices post 2006

Lab assignment - 1

Write a single program with 2 parameters: When parameter 1 is a 1:

Open a test file, (e.g.; “xyz.txt”) Compress it using simple Huffman compression, using the

frequency table from my FTP site Output compressed file (e.g.; “xyz.enc”) to SAME folder as

When parameter 1 is a 2: Open compressed file “xyz.enc” Decompress the input file Output file: “xyz.dec” so it can be compared to “xyz.txt”

Parameter 2 is the full input file path & name (i.e.; file names MUST NOT be hard-coded)

Remember: a code can be a single bit!

Working with Images

Modeling

Containers

A container is a FILE format, NOT a code scheme

E.g.; AVI is a container formatFormat for storageIndependent of encoding or content

Others:Ogg, ASF, QuickTime, RealMedia, Matroska,

DivX, and MP4.

Pixels A pixel is 3 color-dots (squares) in a collection of dots

(squares) making up the picture. Each color-dot is for one of the three primary colors,

RGB. Minimum of 1 byte per color (depending on bit-depth,

which varies with camera), thus at least 3 bytes per pixel.

A 10MP camera (30 million color-dots) needs 30M bytes

This gets compressed by the camera (JPEG format) Final file size = 30 million bytes divided by the amount

of compression (compression ratio). An 8:1 compression ratio would reduce that 30 million

bytes to 3.75 megabytes (as done on a 4 MP camera) A RAW file has NO compression

Image creation

Basic mechanismsDrawing

Line BrushModeling

Modeling/rendering programs OpenGL

Photography Film Digital

Working Definitions - 1

Graphic Model data structure nodes represent random variablesPairs of nodes connected by arcs correspond

to variables that are not independent Graphic modeling

using a Graphic Model to simulate a real-world object (this is not a formal definition)

Rendering generating a 2D image from a 3D graphic model

Working Definitions - 2

Geometric primitives – Points, line segments and polygonsDescribed by vertices

Control points – Special points attached to a node on a Bézier

curveAlter the shape and angle of adjacent curve

segment Evaluators –

Functions that interpolate a set of control points

Produce a new set of control points

Renderman Interface Bytestream

A standardized interface Created by modeling programs Input to rendering programs A plaintext file

Contexts

openGL 3.0 (2.0 + deprecated functions) openGL 3.1 only newer graphics cards

Many <= 3.0 functions deprecatedMany actions now done via shaders1st create a context (like the chicken & the

egg) create an old (e.g.; 3.0) context activate it create the new context deactivate old context

Old context needed to create new one

OpenGL 2.0 Fixed Function Pipeline

Vertex Data

Frame Buffer

Vertex Processor

Fragment Processor

Pixel Data

Per-vertex operations:• Eye-space coordinates• Colors• Texture coordinates• Fog coordinates• Point size

OpenGL 2.0 Vertex Processor Pipeline

Vertex Coordinates

Normal Vector

Color Values

Texture Coordinates

Fog Coordinates

Model View Matrix

Texture Matrix

Projection Matrix

Primitive Setup

Clipping

Vertex Shaderreplaces these

Fragment Processing

Color Summation

Per-pixel Fogging

Fragment Tests

Frame Buffer

Texture Mapping

Bitmaps/PixelRectangles

From primitive setup

fragment shader replaces these

openGL 3.1

Using shaders & Vertex Array ObjectsglBindVertexArray(my_vao_ID[0]); //

select 1st VAOglDrawArrays(GL_TRIANGLES, 0, 3); // draw 1st

objectnote difference from glBegin (GL_POLYGON)….

Note: name of out(put) variable in vertex shader must be the same as in(put) variable in fragment shader .i.e. vertex -> fragment (as in original pipeline)

Lab 2- basic modeling Write a program using the OpenGL 2.0 interface:

Create 3 figures: Triangle (2D) Rectangle (2D) Irregular pentahedron (5-sided, 3D figure) (a pyramid)• See: http://en.wikipedia.org/wiki/Pentahedron for examples• ANY one Vertex pinned at 0,0,0• Allowed to be non-equilateral

Draw all 3 axes (optional, but HIGHLY recommended) The triangle is within the bounds of the rectangle

(or vice-versa), both objects in same plane, different colors The pyramid must have different colors on all 5 sides Create movement controls for the pyramid:

Cursor keys ←→↑↓ change camera location for world view L & R keys rotate pyramid (CW/CCW) about Z-axis Pinned pyramid Vertex STAYS at 0,0,0 The pyramid rotates, the “camera” position remains fixed

Some Examples for lab 2

6-vertex pentahedronValid for lab

Still has 5 sides!

OpenGL

PC RequirementsOPENGL library - for manipulating the model

opengl32.lib opengl32.dll (comes with Windows/XP & 7) glu32.dll “ glu.h and gl.h “

Window Control Glut - note the “t” after the glu

http://www.opengl.org/resources/libraries/glut/glut_downloads.php#windows glut32.dll ”glut32.lib and here tooglut.h

FreeGlut (newer – Open Source)http://freeglut.sourceforge.net/ freeglut.dllfreeglut.libglut.h

glut.h does a #include of gl.h and glu.h© D.J. Foreman 2009

Programming in OpenGL

Define window Define objects Initialize “callback” functions Initialize window Run the gl main loop

OpenGL Program Structure

Two parts1. Modeling, coloring, etc.

Use standard C code, with calls to OpenGL functions

Your program runs as subroutines WITHIN the OpenGL MainLoop

2. Callback functions Called by OpenGL, from OUTSIDE your program Display Reshape

Purpose of “registering” callbacks passes a pointer to your functions allows OpenGL to call them.

OrthographicAll views are 2-dimensionalNot good for games ignores the z-axis

PerspectiveSee model from “camera position” via

“viewport”

cameraviewport

Program structure

Movement functions Shape defining functions (lines, polygons,

etc.) Reshape function (for window re-sizing) Init function Display function Main (includes call to glutMainLoop)

NOTE: gl, glu & glut prefixes on functions.Be careful!

Skeleton of program -1#include <GL/glut.h>#include <stdio.h>#include <math.h>#include <stdlib.h>float ex,ey,ez,theta;void leftMotion (int x, int y);void rightMotion (int x, int y); GLfloat pvertices [][3]= { }; // and then their colors GLfloat pcolors[][3]={ };

// now define the polygon that USES those vertices //define any ONE face of the pyramid at a time

void pface(int a, int b, int c) // pface is a name I made up for “pyramid face”

{// 3 vertices define a faceglBegin(GL_POLYGON);glEnd();

Skeleton of program 2void draw_pyramid() // implement the faces of the figure

{ glPolygonMode (GL_FRONT_AND_BACK,GL_FILL);}

void draw_square(){}void draw_triangle(){} void draw_axes(){

glPushMatrix ();glBegin(GL_LINES); // as pairs of points (default action of GL_LINES)glEnd();glPopMatrix ();

Skeleton of program 3void dj_display(){ /* this is the function that draws the graphic object in the

pre-created window */glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT); /* clear the window */glLoadIdentity();// eye, at upgluLookAt(ex, ey, ez, 0,0,0, 0,1,0); draw_square();draw_triangle();draw_axes(); //last in code, means display on top.draw_pyramid();// now draw the pyramidglFlush();glutSwapBuffers ();

Skeleton of program 4int main(int argc, char*argv[]){

glutInit(&argc, argv);glutInitWindowSize(wd,ht);glutInitWindowPosition(wx,wy);glutCreateWindow("DJ's 1st"); // define name on windowglutSpecialFunc(myspecialkeys);

/* register the call-back functions with Glut*/glutKeyboardFunc(mykey);glutDisplayFunc(dj_display); // more setupglutReshapeFunc(dj_reshaper);dj_init();

// Some texts show init being called AFTER the glutDisplayFunc call,// but it doesn't actually CAUSE display action, it just sets up the

environment.glutMainLoop(); // last (& the only real) executable stmt in programreturn 0;

Basic Functions in “main”

Register your “callback” functionsglutSpecialFunc (your function name);glutKeyboardFunc (your function name);display, reshape

Running the programdj_init(); // your init routine (if any)glutMainLoop();

Basic Display Function

glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

glLoadIdentity();// eye_point, at(x,y,z) up

(x,y,z)gluLookAt (ex, ey, ez, 0,0,0, 0,1,0); draw_triangle/rectangle/pyramid, etcdraw_axes;glutSwapBuffers ();glFlush();

Basic Reshape Function

void reshape (int w, int h) {

glViewport (0, 0, w, h);glMatrixMode (GL_PROJECTION);glLoadIdentity ( );glOrtho(….);glMatrixMode (GL_MODELVIEW);

Drawing

Last drawn object is in “FRONT”MUST set bit depth AND enable bit depth test

RotationglRotate(Ѳ, x,y,z)

operates along a vector starting at 0,0,0Other rotations

Requires pre-multiplication of matrices with the identity matrix

Photography (film) Silver halide crystals (AgCl, AgBr, AgI)

Exposure to light turns them blackDeveloper removes the loose (exposed) halide leaving pure

silverFixing bath flushes out unexposed AgHalide

Greatest desire of photographers: a medium withHigh speed (gathers light quickly)Low noise (no undesired artifacts)High resolution (very detailed images)

Visible lines per mm (lpm) at a specified contrast level

Notes:Larger “clumps” are faster, but limit resolutionSmaller “clumps” are hard to coat evenlyRandomness of coating prevents Moiré patternshttp://en.wikipedia.org/wiki/Moir%C3%A9_pattern

FYI – a little chemistry

Ag+Br- + hv → Ag+ + Br + e-

1. Radiation frees the Br2. 1 Ag ion + 1 electron (Ag+ + e- → Ag0) -> 1 Ag

atom.3. Neighbors are now “sensitized” 4. Developing converts unexposed AgBr to AgS5. AgS & Br are washed away

This is one Ag “grain” in the “latent image”.

crystal

Radiation (light)

Resolution 35 mm film for comparison

A 36 x 24 mm frame of ISO 100-speed film contains (≈) the equivalent of 20 million pixels. 1 There are NO pixels in film!

Full-frame digital (36 x 24mm) Canon EOS 5D, Nikon D3 (21MP) - $5K2

Medium format digital (6 x 4.5cm) Phase One P40+ (39MP) ($22K)

APS-C sized (≈24x16mm) Nikon D90 (12.3MP) - $900, Canon Rebel (15MP) $700 Used in most DSLR’s

Other SONY Alpha (note: image ratio 4/3)

1 Langford, Michael. Basic Photography (7th Ed. 2000). Oxford: Focal Press. ISBN 0 240 51592 7.

2 Prices as of 2009, given for comparison purposes only

Photography (digital)

Image capture formatsRAW – 3 separate images (RGB)

[12 bits/pixel * (4288 * 2848)]/8=18,318,336 bytes per picture

JPEG – compressed (16x, 8x, 4x)Some cameras do BOTH (RAW + JPEG) for each

image Pixel notes:

Sensor size 35mm (or larger) vs. APS-CPixel count – any increase →decrease in pixel size Pixel size – smaller pixels can provide

Greater resolution (finer lines) Lower light sensitivity More “noise” (incorrect values)

Image Manipulation

Photographic imagesGimp, Photoshop, etc

ModelingOpenGL – for creating and lighting a modelmodeling programs

Rendering converting a 3D (possibly wireframe) model

to a 2D image, then lighting and (possibly) shading it

Ray tracing another way of lighting & shading an imagevery CPU intensive

GimpGnu Image Manipulation

Program

Operational concepts

3 windows:Image – contains the actual resultsTools – operators, such as clone, paint, etcLayers – portions of the final image

Avoids need for changes to original Stackable Allows separation of collections of changes Allows complex changes to be applied

independently of other changes

Gimp - lab

Get a digital landscape or cityscape image

Get a picture of yourself Insert the image of yourself into the

‘scape as a layer Save the new image as a new JPG file

Video games vs. Movies

Elements to manipulateContent PerspectiveLighting/shadingSequence Coloring

Video game imagesDynamic

Movie imagesPre-determined

Developed at CMU

Language-free programming environment

Point & click usage

Rapid prototyping

Alice environment List of “world” objects

Insert into methodsModify characteristics (length, width, etc.)

List of world details Properties Methods (user created)Functions (built-in methods)

World window (results) Method builder

Alice - Programming Programmer

Selects “verbs” from list For While Etc.

Applies values for properties Statement structure pre-defined

Blocks pre-defined Function calls for if… then… else

No need to learn a “language”

Alice Lab

Open any of the Alice worlds Apply the following rules

1. Display 3 articulated characters (A, B and C)2. A flips onto its head and rotates slowly (5

times)3. B waves both of its arms slowly (5 times)4. C walks around A and B while (2 and 3

happen)5. C changes direction and walks around A and

B (while 2 and 3 repeat)6. Stop

Timing, size, shape, position are your choice

STEGANOGRAPHY and LSB analysis

What is it? Hiding a message in plain sight

Inside another messageOriginal is called the “cover”

Presence of message is not obvious Can be done with text or graphics

How is it done? Many algorithms for hiding a message Embedding is easier than detection Extraction is straight-forward if:

you know there is a hidden messageyou know the algorithm used

Can be very complex to detect & extract

LSB embedding Concept:

Change the least significant bit of a set of bytes 1→0 and 0→1 For all bytes

Repeat for multiple sets of bytes Example with grayscale images

One pixel is 8 bits Change the last bitChanges that pixel’s shade VERY slightly.Repeat for every pixel

LSB embedding - algorithmEmbedding function Emb (using Matlab or Freelab syntax)

c = imread(‘my_decoy_image.bmp’); % Grayscale cover image% ‘b’ is a vector of m bits (secret message)

k = 1; % Counterfor i = 1 : height for j = 1 : width LSB = mod(c[i, j], 2); if LSB = b[k] | k > m s[i, j] = c[i, j]; else

s[i, j] = c[i, j] + b[k] – LSB; end k = k + 1; endendimwrite(s, ‘stego_image.bmp’, ‘bmp’); % Stego image “s” saved to disk

imread The return value “c” is an array

containing the image data. If the file contains a grayscale image, “c” is an

M-by-N array. If the file contains a truecolor image, “c” is an

M-by-N-by-3 array. The class of “c” depends on the bits-per-

sample of the image data, rounded to the next byte boundary. E.g.; imread returns 24-bit color data as an array

of uint8 data because the sample size for each color component is 8 bits.

LSB extraction - algorithmExtraction function Ext (Matlab syntax)

s = imread(‘stego_image.bmp’); % Grayscale stego imagek = 1;for i = 1 : height for j = 1 : width if k m b[k] = mod(s[i, j], 2); k = k + 1; end endend

% b is the extracted secret message as a bit string

Properties of LSB flipping

LSBflip(x) = x + 1 – 2(x mod 2)

FlipLSB(x) is idempotent, e.g., LSBflip(LSBflip(x)) = x for all x

LSB flipping induces a permutation on {0, …, 255}

0 1, 2 3, 4 5, …, 254 255

LSB flipping is “asymmetrical” (e.g., 3 may change to 2 but never

| LSB(x) – x | = 1 for all x (embedding distortion is 1 per pixel)

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