Graphics Raster Graphics cgvr korea ac kr Graphics

Graphics Raster Graphics 고려대학교 컴퓨터 그래픽스 연구실 cgvr. korea. ac. kr Graphics Lab @ Korea University

Contents n Display Hardware n n How are imaging system organized Output Primitives n n How are images display? Raster Graphics Systems n n CGVR How can we describe shapes with primitives? Color Models n How can we describe and represent colors? cgvr. korea. ac. kr Graphics Lab @ Korea University

Bresenham’s Line Algorithm n CGVR Accurate and Efficient Use only incremental integer calculations n Test the sign of an integer parameter n n Case) Positive Slope Less Than 1 n After the pixel (xk, yk) is displayed, next which pixel is decided to plot in column xk+1? (xk+1, yk) or (xk+1, yk+1) yk+1 yk xk xk+1 cgvr. korea. ac. kr Graphics Lab @ Korea University

Bresenham’s Algorithm(cont. ) n CGVR Case) Positive Slope Less Than 1 n y at sampling position xk n Difference d 1– d 2 < 0 (xk+1, yk) d 1– d 2 > 0 (xk+1, yk+1) n Decision parameter cgvr. korea. ac. kr yk+1 yk d 2 d 1 xk xk+1 Graphics Lab @ Korea University

Bresenham’s Algorithm(cont. ) n CGVR Case) Positive Slope Less Than 1 n Decision parameter of a starting pixel (x 0, y 0) cgvr. korea. ac. kr Graphics Lab @ Korea University

Bresenham’s Algorithm(cont. ) n CGVR Algorithm for 0<m<1 n Input the two line endpoints and store the left end point in (x 0, y 0) n Load (x 0, y 0) into the frame buffer; that is, plot the first point n Calculate constants Δx, Δy, 2Δy, and 2Δy− 2Δx, and obtain the starting value for the decision parameter as n At each xk along the line, start at k =0, perform the following test: n o If pk < 0, the next point to plot is (xk+1, yk) and o Otherwise, the next point to plot is (xk+1, yk+1) and Repeat step 4 Δx times cgvr. korea. ac. kr Graphics Lab @ Korea University

Polygons n CGVR Filling Polygons n Scan-line fill algorithm o n Boundary fill algorithm Inside-Outside tests 1 2 3 4 cgvr. korea. ac. kr 5 6 7 8 9 11 10 5 6 7 8 9 4312 Graphics Lab @ Korea University

Scan-Line Polygon Fill n CGVR Topological Difference between 2 Scan lines y : intersection edges are opposite sides n y’ : intersection edges are same side n y 1 y’ cgvr. korea. ac. kr 2 2 1 1 Graphics Lab @ Korea University

Scan-Line Polygon Fill (cont. ) n CGVR Edge Sorted Table B y. C y. B x. C 1/m. CB y. D y. C’ x. D 1/m. DC y. E x. D 1/m. DE y. A y. E x. A 1/m. AE y. B x. A 1/m. AB C C’ E D A 1 Scan-Line Number 0 cgvr. korea. ac. kr Graphics Lab @ Korea University

Inside-Outside Tests n CGVR Self-Intersections n Odd-Even rule n Nonzero winding number rule exterior interior cgvr. korea. ac. kr Graphics Lab @ Korea University

Boundary-Fill Algorithm n CGVR Proceed to Neighboring Pixels 4 -Connected n 8 -Connected n cgvr. korea. ac. kr Graphics Lab @ Korea University

Antialiasing n CGVR Aliasing n Undersampling: Low-frequency sampling original sample reconstruct Nyquist sampling frequency: n Nyquist sampling interval: n cgvr. korea. ac. kr Graphics Lab @ Korea University

Antialiasing (cont. ) n CGVR Supersampling (Postfiltering) n Pixel-weighting masks Area Sampling (Prefiltering) n Pixel Phasing n Shift the display location of pixel areas n Micropositioning the electron beam in relation to object geometry n cgvr. korea. ac. kr Graphics Lab @ Korea University

Supersampling n CGVR Subpixels n Increase resolution 22 (10, 20): Maximum Intensity 21 (11, 21): Next Highest Intensity (11, 20): Lowest Intensity 20 10 cgvr. korea. ac. kr 11 12 Graphics Lab @ Korea University

Supersampling n CGVR Subpixels n Increase resolution 22 (10, 20): Maximum Intensity 21 (11, 21): Next Highest Intensity (11, 20): Lowest Intensity 20 10 cgvr. korea. ac. kr 11 12 Graphics Lab @ Korea University

Pixel-Weighting Masks n CGVR Give More Weight to Subpixels Near the Center of a Pixel Area cgvr. korea. ac. kr 1 2 2 4 1 2 1 Graphics Lab @ Korea University

Area Sampling n CGVR Set Each Pixel Intensity Proportional to the Area of Overlap of Pixel n 2 adjacent vertical (or horizontal) screen grid lines trapezoid 22 (10, 20): 90% 21 (10, 21): 15% 20 10 cgvr. korea. ac. kr 11 12 Graphics Lab @ Korea University

Filtering Techniques n CGVR Filter Functions (Weighting Surface) Box Filter cgvr. korea. ac. kr Cone Filter Gaussian Filter Graphics Lab @ Korea University

Contents n Display Hardware n n How are imaging system organized? Output Primitives n n How are images display? Raster Graphics Systems n n CGVR How can we describe shapes with primitives? Color Models n How can we describe and represent colors? cgvr. korea. ac. kr Graphics Lab @ Korea University

Electromagnetic Spectrum n CGVR Visible Light Frequencies Range between Red: 4. 3 x 1014 hertz (700 nm) n Violet: 7. 5 x 1014 hertz (400 nm) n cgvr. korea. ac. kr Graphics Lab @ Korea University

Visible Light n CGVR The Color of Light is Characterized by Hue: dominant frequency (highest peak) n Saturation: excitation purity (ratio of highest to rest) n Brightness: luminance (area under curve) n White Light cgvr. korea. ac. kr Orange Light Graphics Lab @ Korea University

Color Perception n CGVR Tristimulus Theory of Color n Spectral-response functions of each of the three types of cones on the human retina cgvr. korea. ac. kr Graphics Lab @ Korea University

Color Models n n n CGVR RGB XYZ CMY HSV Others cgvr. korea. ac. kr Graphics Lab @ Korea University

RGB Color Model n Colors are Additive CGVR R G B 0. 0 1. 0 0. 0 Black 0. 0 Red 0. 0 Green 1. 0 Blue 0. 0 Yellow 1. 0 0. 0 1. 0 cgvr. korea. ac. kr Color 1. 0 Magenta 1. 0 Cyan 1. 0 White Graphics Lab @ Korea University

RGB Color Cube cgvr. korea. ac. kr CGVR Graphics Lab @ Korea University

RGB Spectral Colors n CGVR Amounts of RGB Primaries Needed to Display Spectral Colors cgvr. korea. ac. kr Graphics Lab @ Korea University

XYZ Color Model (CIE) n CGVR Amounts of CIE Primaries Needed to Display Spectral Colors cgvr. korea. ac. kr Graphics Lab @ Korea University

CIE Chromaticity Diagram n CGVR Normalized Amounts of X and Y for Colors in Visible Spectrum (white) cgvr. korea. ac. kr Graphics Lab @ Korea University

CIE Chromaticity Diagram Define Color Gamuts cgvr. korea. ac. kr Represent Complementary Color CGVR Determine Dominant Wavelength and Purity Graphics Lab @ Korea University

RGB Color Gamut n CGVR Color Gamut for a Typical RGB Computer Monitor (green) (red) (blue) cgvr. korea. ac. kr Graphics Lab @ Korea University

CMY Color Model n Colors are Subtractive CGVR C M Y Color 0. 0 1. 0 0. 0 White Cyan Magenta Yellow Blue 1. 0 0. 0 1. 0 cgvr. korea. ac. kr 1. 0 Green 1. 0 Red 1. 0 Black Graphics Lab @ Korea University

CMY Color Cube cgvr. korea. ac. kr CGVR Graphics Lab @ Korea University

HSV Color Model n CGVR Select a Spectral Color (Hue) and the Amount of White (Saturation) and Black (Value) cgvr. korea. ac. kr Graphics Lab @ Korea University

HSV Color Model cgvr. korea. ac. kr CGVR H S 0 60 120 180 240 300 * * * 1. 0 1. 0 0. 0 * V Color 1. 0 Red 1. 0 Yellow 1. 0 Green 1. 0 Cyan 1. 0 Blue 1. 0 Magenta 1. 0 White 0. 5 Gray 0. 0 Black Graphics Lab @ Korea University

HSV Color Model n CGVR Cross Section of the HSV Hexcone cgvr. korea. ac. kr Graphics Lab @ Korea University