1. Mohammed AM Dwikat CIS Department dwikatmo@najah.edu Digital Image

2. To discuss Image fundamentals Image Formation Raster mages Vector Images Rendering Multimedia I2

3. Digital Image Image can be defined as a 2-D function f(x,y), where x and y are spatial coordinates and the amplitude of f at any pair of coordinates (x,y) is called the intensity/gray level of the image at that point When the image is gray scale, intensity values represent the range of shades from black to white. For a color image the intensity values are represented as a combination of R, G, B Can be considered as comprising x X y number of elements (picture elements, image elements, pels, pixels), each of which has a location and value. Multimedia I3

4. Image Formation Pixel values are proportional to the energy/ electromagnetic waves radiated from the source It implies this value cannot be negative, ranges from 0 to +ve infinity Function f(x,y) characterized by components Illuminationi(x,y), value ranging from 0 to infinity Reflectancer(x,y), value ranging from 0 to 1 f(x,y)= i(x,y) x r(x,y) f(x,y) lies between L min to L max scaled to [0,L-1], where 0 representing black and L-1 representing white, the intermediate values are the shades of gray from black to white Multimedia I4

5. Image Formation Multimedia I5

6. Image Formation Multimedia I6

7. Image Formation Multimedia IMohammed Dwikat7 256 gray levels (8bits/pixel) 32 gray levels (5 bits/pixel) 16 gray levels (4 bits/pixel) 8 gray levels (3 bits/pixel) 4 gray levels (2 bits/pixel) 2 gray levels (1 bit/pixel)

8. Image Formation Output of image sensors are continuous voltage waveform, digitization is necessary for further processing Digitizing the coordinate positions are called sampling Digitizing the amplitude values are called quantization Number of gray levels will be in an integer power of 2 L=2 k, [0…L-1] Number of bits needed to store an image b=M x N Image is k bit image if it has 2 k gray levels 8 bit image has 256 gray levels Multimedia I8

9. Computer Graphics Vector Graphics Bitmap Images Combining vectors and bitmaps Multimedia I9

10. Models of Bitmapped Graphics Raster images (Bitmap Images)- grids of dots, or pixels, each pixel containing colour information modeled by an array of pixel values Bitmapped graphics does not use bitmaps (except for pure monochrome images) it use pixel maps Multimedia I10

11. Raster - 8 * 6 pixels Multimedia IMohammed Dwikat11

12. Raster - 16 * 12 pixels Multimedia IMohammed Dwikat12

13. Bit depth Bit Depth is the Number of bits used to represent every pixel in a digital image. It defines the number of colours available to each pixel within an image. Multimedia I13

14. Bit depth Bit DepthColours Available 1-bit black and white 2-bit4 colors 4-bit 16 colors 8-bit256 colors 8-bit greyscale256 shades of grey 16-bit65536 colours 16.7 million colours 24-bit 16.7 million colours 16.7 million colours 32-bit16.7 million colours + 256 Levels of transparency Multimedia I14

15. 8 bit - 256 colours Multimedia I15

16. 24 bit bmp 240 * 180 = 43200 pixels File size: 43200 *3 = 129600 bytes = 127 KB Actual size 127 KB 8 bit bmp 240 * 180 = 43200 pixels File size: 43200 *1 = 43200 bytes = 42 KB Actual size 44 KB

17. 4 bit bmp 240 * 180 = 43200 pixels File size: 43200 *0.5 = 21600 bytes = 21 KB Actual size 22 KB Gif 240 * 180 = 43200 pixels File size: Compressed format Actual size 3 KB

18. File size & number of pixels Multimedia IMohammed Dwikat18 More pixels  lines less jagged, but bigger filesize. 8 * 6 = 48 pixels 16 * 12 = 192 pixels Width & height * 2 : filesize * 4 48 192

19. File size & number of pixels Multimedia IMohammed Dwikat19 More pixels  lines less jagged, but bigger filesize. 640 * 480 = 307,200 1280 * 960 = 1,228,800 Width & height * 2 : filesize * 4 307200 1228800

20. Models of Vector Graphics Are Images that stored as a mathematical description of a collection of individual lines, curves and shapes making up the image e.g. line = two end points Displaying a vector image requires some computation to be performed in order to interpret the model and generate an array of pixel to be displayed The process of interpreting the vector description known as rasterizing Multimedia I20

21. Vector Graphics Scalable Resolution independent No background Cartoon-like Inappropriate for photo-realistic images Metafiles contain both raster and vector data Multimedia I21

22. Vector Graphics Points can be identified by coordinates Lines and shapes can be described by equations Approximating abstract shapes on a grid of finite pixels leads to `jaggies Anti-aliasing can offset this effect Bezier curves are drawn using four control points Bezier curves can be made to join together smoothly into paths Paths and shapes can be stroked and filled Multimedia I22

23. Vector Graphics Geometrical transformations translation, scaling, rotation, reflection and shearing - can be applied easily to vector shapes Three approaches to 3-D modeling constructive solid geometry free-form modeling procedural modeling 3-D rendering models the effect of light and texture, as well as displaying the modeled objects in space Ray tracing and radiosity are computationally expensive rendering algorithms that can produce photo-realistic results Multimedia I23

24. Vector Graphics Vector image - line from x 1,y 1 to x 2,y 2 Multimedia IMohammed Dwikat24

25. Vector Graphics Tools Adobe Illustrator CorelDraw Macromedia FreeHand XARA X Most can export your work to bitmap images Multimedia I25

26. Metafile Format Used for vector graphics Can embed bitmap images Collection of Graphics Device Interface (GDI) functions “Rasterization” process Default extension.WMF Less space Structure header size of the file # of drawing objects list of records Multimedia I26

27. Rendering In 3D, we have a mathematical model of objects in space, but we need a flat picture Viewpoint Position of camera Scaling with distance Lighting: position, intensity, type Interaction of light: underwater, smoke-filled room Texture Multimedia I27

28. Rendering Wire frame Hidden surface removal Surface properties Color and reflectivity Lights Shading A color for each polygon Interpolate color Multimedia I28