CS 559 Computer Graphics Prof Stephen Chenney Fall

CS 559: Computer Graphics Prof Stephen Chenney Fall 2004 http: //www. cs. wisc. edu/~cs 559 -1 09/07/04 © 2002 -2004 University of Wisconsin

Today • Course overview and information • Digital Images • Homework 1 – due Sept 14 in class 09/07/04 © 2002 -2004 University of Wisconsin

What is Computer Graphics? • Technically, it’s about the production, manipulation and display of images using computers • Practically, it’s about movies, games, design, training, art, advertising, communication, … 09/07/04 © 2002 -2004 University of Wisconsin

This Course: Building Blocks • Images and computers – Sampling, Color, Filters, … • Drawing in 2 D – Drawing lines and triangles, clipping, transformations • Drawing in 3 D – Viewing, transformations, lighting, real-time graphics • Modeling in 3 D – Describing volumes and surfaces, drawing them effectively • Miscellaneous topics – Raytracing, animation, … 09/07/04 © 2002 -2004 University of Wisconsin

People • Prof. Stephen Chenney – Room 6387 – Office Hours: TBD – schenney@cs. wisc. edu • TA: Leo Chao – Room 1346 – Office Hour TBD – chaol@cs. wisc. edu Send all class email to cs 559 -1@cs. wisc. edu It gets the fastest response. 09/07/04 © 2002 -2004 University of Wisconsin

Web and Email • The class web site is http: //www. cs. wisc. edu/~cs 559 -1 – – It is updated very frequently Lecture notes are put online before class, and updated after class Additional resources and links are provided Reading for future classes is listed • Email is sent out on the class mailing list – This list sends email to your official university email account • Check it regularly or set up forwarding – All notices are sent out on the mailing list, including things not mentioned in class – Only registered students get email • You read an archive at https: //www-auth. cs. wisc. edu/lists/classes/ 09/07/04 © 2002 -2004 University of Wisconsin

CS Computer Account • Everyone in the class needs a Computer Science department computer account – For completing and submitting projects • If you don’t have one, go to the CSL on the 2 nd floor • CS 559 provides you with a Windows account – You will only have a Unix account if you are taking some other course 09/07/04 © 2002 -2004 University of Wisconsin

Textbooks and Readings • Peter Shirley, “Fundamentals of Computer Graphics”, A. K. Peters, 2002 • Woo et. al. , "Open. GL Programming Guide", Third or Fourth Edition, Adison-Wesley, 1999 or 2003 – The definitive guide to Open. GL, and a reasonable description of general real-time 3 D graphics – It doesn’t really matter which edition – the differences are not pertinent to this class • Class readings – Online via the library’s reserve system – see class web page – A collection of papers, textbook chapters, and other documents – Some essential material not contained in the textbook 09/07/04 © 2002 -2004 University of Wisconsin

Projects • There will be three projects for the course, spread evenly through the semester • Project 1: Image editing • Project 2: Running a maze • Project 3: Building a virtual theme park • You must submit all three in order to pass the course – This rule has never been waived 09/07/04 © 2002 -2004 University of Wisconsin

Homeworks • There will be a homework every two weeks or so • They are intended primarily to explore topics further and to prepare you for the exams • They will be graded, but only the best five will count • Some essential techniques will be presented only in homework – For example, an review of linear algebra 09/07/04 © 2002 -2004 University of Wisconsin

Grading (approximate) • • • 45% Midterm and Final 45% Projects 10% Homework Everyone must write up their own homework For projects 1 and 3, you have the option of working in pairs 09/07/04 © 2002 -2004 University of Wisconsin

Lab Facilities • Room B 240 contains machines for use in this class • They have adequate hardware (circa 2001) and the software to make it work • Students in CS 559 have priority in the lab • There are benefits to working in a lab with your classmates – For instance, the blackboards frequently display useful hints that someone else scrawled – But they also sometimes have incorrect information!! 09/07/04 © 2002 -2004 University of Wisconsin

Software Infrastructure • FLTK will be the user interface toolkit – Provides windows, buttons, menus, etc – C++ class library, completely portable – We are currently at version 1. 1. 0 rc 6, available for free: www. fltk. org • Open. GL will be the 3 D rendering toolkit – Provides an API for drawing objects specified in 3 D – Included as part of Windows and in most Unix distributions • Although getting hardware acceleration may take some doing • Visual Studio. NET (Visual C++ 7. 1) will be the programming environment for grading • To be graded, your projects must compile under Visual C++ on the machines in room B 240 09/07/04 © 2002 -2004 University of Wisconsin

C++ • This is probably the first, and only, class in which you must complete large software projects in C++ without step by step instructions • There is a great deal of freedom in the projects, which requires that you do your own software design • If you are not comfortable in C++, you will have to take action • There are tutorials intended to teach you C++ assuming you know Java: – http: //www. cs. wisc. edu/~hasti/cs 368/Cpp. Tutorial/index. html – These are intended for the course CS 368, but just do the tutorials • The transition to C++ was one of the biggest issues for past CS 559 students – Visual Studio also causes issues – we will provide a transition tutorial 09/07/04 © 2002 -2004 University of Wisconsin

Adding the Class • Everyone should be able to add at this point • If not, email cs 559 -1@cs. wisc. edu with your name, ID and major – If the system gave you a reason for denying registration, include it in your email • You have to wait a couple of days after adding before you can get a CS computer account 09/07/04 © 2002 -2004 University of Wisconsin

Admin Questions? 09/07/04 © 2002 -2004 University of Wisconsin

Images • An image for our purposes is an abstract concept – It has no existence until it is displayed • An image is intended to describe the light that arrives at your eyes when you view it – You can be even more abstract: image describes what you should think when you see it • Different display devices convey the image content in different ways – e. g. Print and computer monitors use two fundamentally different approaches – The same image may look different on different monitors • Who cares? 09/07/04 © 2002 -2004 University of Wisconsin

Image Formats • We are familiar with many forms of image: – – – Photographs Paintings Sketches Television (NTSC, PAL-SECAM) Digital formats (JPEG, PNG, GIF, etc. ) • Each form has its own way of obtaining and storing the information content • We are primarily concerned with digital formats, but we will also discuss NTSC 09/07/04 © 2002 -2004 University of Wisconsin

Digital Images • Many formats (100 s) exist for storing images on a computer • There are some conflicting goals: – The storage cost should be minimized – The amount of information stored should be maximized • The size of something and the amount of information is contains are not the same thing – Original information versus perceptual equivalence – Tracking ownership may be important • Most formats you are familiar with are raster images 09/07/04 © 2002 -2004 University of Wisconsin

Raster Images • A raster is a regular grid of pixels (picture elements) • Raster image formats store the color at each pixel, and maybe some other information – Easiest is to use a simple array of pixel values – Some formats store the pixel information in very different ways – e. g. a 5 x 3, floating point, grayscale image 0. 25 0. 25 1 0. 25 09/07/04 © 2002 -2004 University of Wisconsin

Vector Images • Vector formats offer an alternative way to store images • The most common use of vector formats are in fonts – images of characters (Postscript, True. Type) • Store images as collections of geometric primitives – E. g. Lines, polygons, circles, curves, … • It is possible to go from a vector image to a raster image – We’ll learn how • It is very hard to go the other way 09/07/04 © 2002 -2004 University of Wisconsin

Trade-Offs • Which format, raster or vector, is easier to: – – 09/07/04 Display? Resize (scale bigger or smaller)? Rotate? Crop (cut bits off at the edges)? © 2002 -2004 University of Wisconsin

Obtaining Digital Images • What are some methods for obtaining a digital image? – – – – 09/07/04 Digital camera Scanning another image Other forms of scanning (eg medical) Editing existing digital images Paint or drawing programs Created from abstract data (e. g. math function plot) Rendered from a scene description … © 2002 -2004 University of Wisconsin

Ideal Images • The information stored in images is often continuous in nature • For example, consider the ideal photograph: – It captures the intensity of light at a particular set of points coming from a particular set of directions (it’s called irradiance) – The intensity of light arriving at the camera can be any positive real number, and it mostly varies smoothly over space – Where do you see spatial discontinuities in a photograph? Film Focal point 09/07/04 © 2002 -2004 University of Wisconsin

Digital Images • Computers work with discrete pieces of information • How do we digitize a continuous image? – Break the continuous space into small areas, pixels – Use a single value for each pixel - the pixel value (no color, yet) – No longer continuous in space or intensity • This process is fraught with danger, as we shall see Continuous Discrete Pixels: Picture Elements 09/07/04 © 2002 -2004 University of Wisconsin

Discretization Issues • Can only store a finite number of pixels – Choose your target physical image size, choose your resolution (pixels per inch, or dots per inch, dpi), determine width/height necessary – Storage space goes up with square of resolution • 600 dpi has 4× more pixels than 300 dpi • Can only store a finite range of intensity values – Typically referred to as depth - number of bits per pixel • Directly related to the number of colors available and typically little choice • Most common depth is 8, but also sometimes see 16 for grey – Also concerned with the minimum and maximum intensity – dynamic range • What is enough resolution and enough depth? 09/07/04 © 2002 -2004 University of Wisconsin

Perceptual Issues • Spatially, humans can discriminate about ½ a minute of arc – At fovea, so only in center of view, 20/20 vision – At 0. 5 m, about 0. 1 mm (“Dot pitch” of monitors) – Sometimes limits the required number of pixels • Humans can discriminate about 8 bits of intensity 129 128 125 – “Just Noticeable Difference” experiments – Limits the required depth for typical dynamic ranges – Actually, it’s 9 -10 bits, but 8 is far more convenient • BUT, when manipulating images much higher resolution may be required 09/07/04 © 2002 -2004 University of Wisconsin

Next Time • Color 09/07/04 © 2002 -2004 University of Wisconsin