1 By Dr. Hany Elsalamony

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3  Computer graphics generally means creation, storage and manipulation of models and images  Such models come from diverse and expanding set of fields including physical, mathematical, artistic, biological, and even conceptual (abstract) structures Frame from animation by William Latham, shown at SIGGRAPH Latham uses rules that govern patterns of natural forms to create his artwork. By Dr. Hany Elsalamony

 Examples: OpenGL™, DirectX™, Windows Presentation Foundation™ (WPF), RenderMan™  Primitives (chars, lines, polygons, meshes,…)  Attributes color line style material properties for 3D  Lights  Transformations  Immediate mode vs. retained mode immediate mode: no stored representation, package holds only attribute state, and application must completely draw each frame retained mode: library compiles and displays from scene graph that it maintains, a complex DAG. It is a display-centered extract of the Application Model 4 By Dr. Hany Elsalamony

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 Computer graphics – process of producing a picture or image using the computer  Computer interfaces popular on personal computers  Desktop publishing  Realistic images generated using mathematical and physical methods 7 By Dr. Hany Elsalamony

 Creating a model  Perform necessary transformation  Lighting and rendering the object  The goal is the creation of an image by writing a program instead of taking a picture with a camera  There exists an analogy between writing graphical programs and taking pictures by a camera 8 By Dr. Hany Elsalamony

 Pixel or “Picture element” is the simplest element in computer graphics  Single location on the computer screen or printout  Value of each pixel is the range from white to black or range of intensities of red, green, blue (RGB) colors. 9 By Dr. Hany Elsalamony

 The pixels of an image are organized into two dimensional grid – frame buffer  Multiple frame buffers can be stored in computer memory  Double buffering – first image is drawn into frame buffer and sent to display. While the user is looking on the display, the next picture is drawing to the second buffer. 10 By Dr. Hany Elsalamony

 Image don’t fill the entire screen but is drawn into a window  Pixels are adressed within the window based on their location  Relative position of each pixel enables moving the window and change its size 11 By Dr. Hany Elsalamony

 Calculating pixel values to create impression of a realistic picture  Simulation of objects from the real word  Approximation of physical properties of objects  Limitations given by computing time and memory space 12 By Dr. Hany Elsalamony

 Modeling – creates an internal representation of the objects in the scene  Rendering – converts the screen description into image  Display – shows the image on the output device 13 By Dr. Hany Elsalamony

Object Specification Model Transformation Scene Description Model Transformation View and Light Specification Clipping and Hidden Surface Removal Shading Image 14 By Dr. Hany Elsalamony

Display Transformation Image Output 15 By Dr. Hany Elsalamony

1. Display of information 2. Design 3. Simulation and animation 4. User interfaces 16 By Dr. Hany Elsalamony

 Display of information Maps GIS (geographic information system) CT (computer tomography) MRI (magnetic resonance imaging) PET (positron-emission tomography) Fluid flow, molecular biology, mathematics… 17 By Dr. Hany Elsalamony

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 Design CAD (computer-aided design): VLSI (very-large-scale integrated) circuits Together with other tools: architecture or interior design 19 By Dr. Hany Elsalamony

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 Simulation and animation Flight simulation – pilot training Games and educational software Benefits:  Less cost  Less danger, e.g. combination with the VR (virtual reality) techniques can help surgical interns and astronauts 21 By Dr. Hany Elsalamony

 User interfaces Friendly working environment: windows, icons, menus, pointing devices 22 Interface for a painting program By Dr. Hany Elsalamony

23 Specifications of the functions in the graphics library The OpenGL graphics system is an Application Programming Interface (API) to graphics hardware. By Dr. Hany Elsalamony

24  Objects  Viewers  Light sources  Material properties By Dr. Hany Elsalamony

25  Position (COP)  Orientation  Focal length  Film plane By Dr. Hany Elsalamony

26  Wireframe  Flat shading HSR (Hidden surface removal)  Smooth shading  Curves and surfaces NURBS, Bezier curves/surfaces  Texture mapping Bump mapping, environmental maps, antialiasing… By Dr. Hany Elsalamony

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29  High-end systems: VRAM or DRAM  Simpler systems: part of memory  Depth: the number of bits per pixel  True color: depth=24  Resolution: the number of pixels in the frame buffer By Dr. Hany Elsalamony

30  Conversion of geometric entities to pixels in the frame buffer High-end systems  Special-purpose processors Simpler systems  A single and shared processor By Dr. Hany Elsalamony

31 CRT (Cathode-ray tube) By Dr. Hany Elsalamony

32  CRT Refresh: at least 50 times per second Interlace and non-interlace systems Color CRTs have three colored phosphors and a shadow mask  Other raster devices: LCD (liquid-crystal displays) Plasma panels and digital projection systems Non-refreshable: printers and plotters By Dr. Hany Elsalamony

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34  Mouse Joystick Data tablet Anything else? Hand Foot Voice Mind? By Dr. Hany Elsalamony

 Image formation Lighting Shading Properties of materials 35 By Dr. Hany Elsalamony

 Object: formed from geometric primitives Points, lines, polygons Vertex (pl. Vertices) is the most primitive one  Viewer: Locations Viewing angles 36 By Dr. Hany Elsalamony

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38 3D world  2D image By Dr. Hany Elsalamony

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40 Synthetic-camera Model Film Plane Projection Plane By Dr. Hany Elsalamony

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42 Penetrating transparent surfaces Reflected by Mirrors Diffuse surfaces Refracted Absorbed By Dr. Hany Elsalamony

43 Visual system does not have the same response to each color. We are most sensitive to green light By Dr. Hany Elsalamony

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45  (x p, y p, -d) is the projection of (x, y, z) By Dr. Hany Elsalamony

46 Bellows Camera Projector By Dr. Hany Elsalamony

47 COP(Center of Projection) Focal Length By Dr. Hany Elsalamony

48 Film Plane Projection Plane By Dr. Hany Elsalamony

49 Clipping Window By Dr. Hany Elsalamony

 Wireframe  Flat shading HSR (Hidden surface removal)  Smooth shading  Curves and surfaces NURBS, Bezier curves/surfaces  Texture mapping Bump mapping, environmental maps, antialiasing… 50 By Dr. Hany Elsalamony

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58 Example: Scene graph By Dr. Hany Elsalamony

59 Early graphics system Compute line segments Draw line segments Very high rate to avoid flickering By Dr. Hany Elsalamony

60 Display-processor architecture By Dr. Hany Elsalamony

61 Arithmetic pipeline: doubling the throughput! Pipeline Architecture: Geometric pipeline By Dr. Hany Elsalamony

62 Arithmetic pipeline: doubling the throughput! Pipeline Architecture: Geometric pipeline By Dr. Hany Elsalamony

 Transformation Conversion between coordinate systems Translation, rotation, scaling Aggregate transforms by matrix multiplications  Clipping Could be further pipelined 63 By Dr. Hany Elsalamony

 Projection Remaining 3D objects are projected into 2D objects Parallel or perspective projections  Rasterization Convert 2D objects into pixels 64 By Dr. Hany Elsalamony

65  Latency  Throughput: How fast we can move geometric entities through the pipeline How many pixels per second we can alter in the frame buffer  Pipeline architecture is not a must Ray tracing or radiosity  for better quality By Dr. Hany Elsalamony

66  Application of computer graphics  A graphics system  Human visual system  Pinhole and synthetic camera models  Image formation  Geometric pipeline  Realistic images may require resolution of up to 4000  6000 By Dr. Hany Elsalamony