I-1 Steps of Image Generation –Create a model of the objects –Create a model for the illumination of the objects –Create an image (render) the result I Computer Graphics Background

I-2 Image Terminology Pixel – picture element –One location in a computer image –Gray scale image has one value –Color image has three values for red, green, and blue Frame buffer –The two-dimensional grid of pixels for an image A window is an area of the computer screen where the image is displayed

I-3 Graphics Pipeline Three main stages –Modeling –Rendering –Display

I-4 Modeling Stage Specifies details of objects in scene –Shape –Materials –Color –Shininess, transparency, translucency –Texture

I-5 Rendering Stage Simulates the flow of light Models the way light interacts with objects –Different materials react with light differently Determines visibility of objects

I-6 Image Display Stage Image display is supported by graphics hardware Different devices output images differently –Manufacturers use different components, which accounts for the difference

I-7 View Information The viewpoint gives the location of the viewer The view direction is a vector specifying the direction the viewer is looking

I-8 Coordinate Systems Object coordinate system –Used to define object shape World coordinate system –Used to position various objects in the scene View coordinate system –Defined by the viewpoint, view direction, and view up direction Window coordinate system –Defines the part of the world that is visible

I-9 Local or object, world, view, and window coordinate systems

I-10 Right-handed vs. left-handed coordinate systems

I-11 Homogeneous Coordinates Locations are typically specified through the (x, y, z) coordinate Homogeneous coordinates add a fourth component to get (x, y, z, w) Typically, the w term will be 1 but transformations may change this If w in (x, y, z, w) is not 1, the actual (x', y', z') coordinate is (x/w, y/w, z/w)

I-12 Color Models Used to specify a color There are many different color models that have different purposes Color can be defined by wavelength –Wavelengths can be combined to produce color

I-13 RGB Color Model Based on red, green, and blue An additive color model –Red, green, and blue light is combined to create different colors Can be shown on a cube with red, green, and blue on the three major axes Shades of gray appear along the main diagonal

I-14 RGB Color Model

I-15 CMY Color Model Based on cyan, magenta, and yellow A subtractive color model –Cyan, magenta, and yellow ink or toner subtract color from white Closely related to the RGB model –C=1.0-R, M=1.0-G, Y=1.0-B CMYK model also includes black to create richer output –K=minimum(C, M, Y), C=C-K, M=M-K, Y=Y-K

I-16 HSV Color Model Based on hue, saturation, and value An artistic model Hue determines color Saturation determines the amount of color –How much white is added to the full color Value indicates the lightness of the color –How much black is added to the full color

I-17 HSV Color Model

I-18 HLS Color Model Based on hue, lightness, and saturation Similar to the HSV color model

I-19 Displaying Images Output devices include: –Monitors –Flat panel displays –Printers –Three-dimensional printers

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