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Computer Graphics 1

Computer Graphics 1. Computer Graphics 1. What is computer graphics? What can it be used for? What will we learn in this course?. Who am I?. A PhD student at the Centre for Image Analysis Working with microscopic images of human cells to e.g. aid a doctor to diagnose cancer.

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Computer Graphics 1

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  1. Computer Graphics 1

  2. Computer Graphics 1 • What is computer graphics? • What can it be used for? • What will we learn in this course?

  3. Who am I? • A PhD student at the Centre for Image Analysis • Working with microscopic images of human cells to e.g. aid a doctor to diagnose cancer.

  4. Centre for Image Analysis

  5. What is Computer Graphics? • Creating and displaying graphics and images with the aid of a computer. • This can be almost anything… but it usually starts with an abstract representation of numbers and ends with something that we can see.

  6. What can it be used for? • Visualization of data • Medicine, science, economics... • Working tool • Graphical User Interfaces (GUI’s), VR... • Entertainment • Computer games, film, art… • Part in telecommunication (decompression) • …

  7. What is the relationship between Computer graphics and Image analysis? They are (almost) each others inverses • In computer graphics we start with a bunch of numbers and parameters and end up with an image. • In image analysis we start with an image and end up with a bunch of numbers.

  8. What will we learn in this course? • How to draw images on a computer screen, points, polygons and objects. • How to create a 3D impression despite our restriction to flat screens. • How to move around in virtual 3D world. • Some tools for modelling a 3D world. • A brief introduction to the OpenGL API.

  9. What we will not learn in this course! :-( • Esthetical aspects of CGX. • How to use 3D-studio, Lightwave, Renderman… • How to render photo realistic images (off-line rendering). • X, DirectX, SDL, Java3D, … and all other API’s out there. • Hardware stuff.

  10. This course • http://www.tdb.uu.se/~grafik/ht01/ • 19 Lectures • 4 Computer ”laborations” • This is time for coding the assignments. • 5 Assignments (which give bonus points on the exam) • This is probably the major part of the work. • A fairly easy exam • If you have done the assignments, this will hardly be of much trouble.

  11. The fast forward version View volume View plane Hidden surface Lightsource Camera or observer Projection 3D 2D Rasterization Shadow Clipping Transformation

  12. The Display PipelineThe order may vary somewhat Polygon in ... Transform Clipping HSR Light calculations ... • Modelling, create objects (this is not really a part of the pipeline) • Transformations, move, scale, rotate… • View transformation, put yourself in the origin of the world • Clipping, cut away things outside the view volume • Hidden surface removal, we don’t see through things • Light and illumination, shadows perhaps • Projection, 3D => 2D • Rasterisation, put things onto our digital screen Texture, shading, image based HSR...

  13. Images in a computer... 94 100 104 119 125 136 143 153 157 158 103 104 106 98 103 119 141 155 159 160 109 136 136 123 95 78 117 149 155 160 110 130 144 149 129 78 97 151 161 158 109 137 178 167 119 78 101 185 188 161 100 143 167 134 87 85 134 216 209 172 104 123 166 161 155 160 205 229 218 181 125 131 172 179 180 208 238 237 228 200 131 148 172 175 188 228 239 238 228 206 161 169 162 163 193 228 230 237 220 199 … just a large array of numbers

  14. To draw images • To write the right numbers at the right places in this large array (the screen buffer). • This is often done by a function called putpixel(x,y,color) • or (if possible) by directly writing in the array buffer[y][x]=color;

  15. Using putpixel, we can draw lines... • and we can draw polygons. • We never need more than triangles i fact. • Triangularisation (cutting polygons into triangles). • Tessellation (cutting polygons into smaller ones). • Triangles are always flat, which is nice.

  16. We put our triangles together to form objects. • We put the objects in a 3D world. • We use a camera model to view the world. • We use transformations to move around in the world, as well as to move objects around in the world. • We add light to get a nice 3D effect. • We remove things we cannot see.

  17. We may speedup things using maps of different types, e.g. textures. • Starting from polygons, it is tedious to build a world. We need modelling tools. Splines and fractals are two such tools.

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