1	Roadmap What is Computer graphics? Raster Graphics (sample based) E.g., “paint” programs Adobe Photoshop Parts of Metacreations Painter Windows Paint Etc.
2	What is Computer Graphics? (1/2) Computer graphics is commonly understood to mean the creation, storage and manipulation of models and images. Such models come from a diverse and expanding set of fields including physical, mathematical, artistic, biological, and even conceptual (abstract) structures.
3	What is Computer Graphics? (2/2) The term “computer graphics” was coined in 1960 by William Fetter to describe new design methods he was pursuing at Boeing. He created a series of widely reproduced images on a pen plotter exploring cockpit design, using a 3D model of a human body.
4	What is Interactive Computer Graphics? (1/3) User controls contents, structure, and appearance of objects and their displayed images via rapid visual feedback Basic components of an interactive graphics system input (e.g., mouse, tablet and stylus, force feedback device, scanner, live video streams…) processing (and storage) display/output (e.g., screen, paper-based printer, video recorder, non-linear editor…) First truly interactive graphics system, Sketchpad, pioneered at MIT by Ivan Sutherland for his 1963 Ph.D. thesis
5	Continuous vs. Discrete Continuous Media such as traditional photography, painting Always another color between any two points of color Discrete Media such as needlepoint, mosaics Colors in an image easily separable into individual units
6	Discrete Data Easy to Digitize If picture (or other data) is already in discrete, separable units, it’s much easier to represent with numbers (i.e., digitize) E.g., text is easy to digitize Digital processes used in weaving, needlepoint, with colors and locations indicated numerically Digital is not same as computer…
7	Raster or Sample-based Graphics Sample-based graphics: discrete elements (aka samples) are used to describe visual information Pixels (picture elements) can be created by digitizing images (e.g., digital camera, scanner) Pixels can be created using a sample-based “painting” program Inputting pixel information by hand (e.g., w/numbers from a computed data set) Aspects of the physical world can be sampled for visualization, e.g., temperature across the US Example programs: Adobe Photoshop™, GIMP™, Adobe AfterEffects™ (it came out of CS123/CS224!) In this coordinate space each pixel is represented by x- and y-coordinates and a color
8	“Brush” Tools c
9	“Natural Media” Brushes Corel Painter
10	GTT and the Art and Science of the Brush Tool DEMO: One tool = brush, spray can, eraser, natural media brushes, etc. In GTT, have to make your own personalized, distinctive “brushes” http://graphics.cs.brown.edu/research/gtt/
11	GTT Flower “Lab” Draw an imaginary flower Can be realistic (if you know something about a real flower) Can be fantastic But has to be recognizable as a flower Make at least 3 different brushes to use while drawing it Experiment with brush size, shape, alpha differences in different areas of brush mask Save final drawing(s) and workspaces.
12	Sampling = Losing Data When you reduce continuous information (done via sampling) to a finite number of elements you LOSE DATA Fortunately, we deal well with lossy noise info (e.g., retinal readout example) You can watch TV, which is often horrible… eye integrates We see what we think we should see… we minimize artifacts based on sampling error Sampling applet http://www.cs.brown.edu/exploratories/freeSoftware/repository/edu/brown/cs/exploratories/applets/sampling/introduction_to_sampling_guide.html Number of samples you may need to take for various purposes a well studied area. (We’ll be exploring this later)
13	“A Pixel is Not A Little Square” What I am about to say is so fundamental that I wish I could shout it from the treetops and have people remember! A pixel is a point sample—that is, the value of a continuous thing at a single point (with zero dimensions). If only this were understood, we might be able to rid the world forever of the misconception that a pixel is a little square. Alvy Ray Smith [Smith 1975] More on this later when we discuss “zooming into” (i.e., scaling) images
14	Pixels, pixels, everywhere…
15	What Can You Do With Sampled Data? Once an image is defined as a pixel-array, it can be manipulated Image editing changes made by user, such as cutting and pasting sections, brush-type tools, and modifying selected areas. Image processing algorithmic operations that are performed on an image (or pre-selected portion of an image) without user intervention. Includes blurring, sharpening, edge-detection, color balancing, rotating, and warping. A pre-processing step in computer vision.
16	Sampling an Image Lets do some sampling of the CIT building A color value is measured at every grid point and used to color a corresponding grid square Note: this poor sampling and image reconstruction method creates a blocky image
17	What’s the Advantage? Once image is defined in terms of colors at (x, y) locations on grid, can change image easily by altering numerical location or color values E.g., if we reverse our mapping above and make 10 = white and 0 = black, the image would look like this: Pixel information from one image can be copied and pasted into another, replacing or combining with previously stored pixels
18	What’s the Disadvantage WYSIAYG (What You See Is All You Get): There is no additional information no depth (3D) information can’t examine scene from a different point of view at most can play with the individual pixels or groups of pixels to change colors, enhance contrast, find edges, etc. But recently, strong interest in image-based rendering to fake 3D scenes and arbitrary camera positions. New images constructed by interpolation, composition, warping and other operations.
19	Thinking With Raster Graphics In artwork the processes and techniques of photography and painting are merging in the art of digital imaging—new “thoughts” expressed Michele Turre: the artist, her daughter, and her mother, all at 3 years of age Image processing in general includes image transformation, and is used for feature detection, pattern recognition, and machine/computer vision, and most recently, for image-based rendering
20	Advances in Image Manipulation People can now mutate into other people or objects through morphing, and can carry on conversations in different times and places Interactive Digital Photomontage, Siggraph 2004 The belief in a very strong connection between photorealistic images, still or moving, and reality is being severed no way to tell if news photos are “real” photographs photographic evidence no longer considered “proof” in a court of law without clear provenance of the image future of the family photo album?
21	Filtering A filter alters a pixel's value by taking not account not only its original value, but that of its neighbors as well Little grid-chart that shows influence of each pixel on final pixel value is called filter kernel
22	GTT Filter Tool
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24	Filtering and Scaling Scaling sometimes called “re-sampling” because changes numbers of pixels in image (either up or down) How to get new pixel values (or decide which to eliminate)? Filters again! In scaling up, filters used to calculate value of new pixels based on original neighbors
25	Scaling for Zooming Scaling with box filter, aka pixel replication This method used for “zooming”—is temporary scaling of an image Not a “close-up” of square pixels…
26	Better Quality Scaling