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Introduction to Computer Graphics Midterm Examination Professor Brogan
Name:____________________________
Honor Pledge: This is a closed-book, closed-notes, independent exam. Please sign the honor pledge: On my honor as a student, I have neither given nor received information on this exam. Signed, ______________________
All coordinate systems will be assumed right-handed.
Display Technology
What is interlaced scanning and why do televisions use this technology?
What is 3:2 Pulldown used for?
Describe the movements and emissions of the electron gun in a CRT when illuminating images on the screen of a non-interlaced raster display device.
True or false, there must be tight synchronization between a raster monitor’s framebuffer, phosphor persistence, and refresh rate? Define these terms and explain.
A pixel of a liquid crystal display could be described as a layer of liquid-crystal material sandwiched between two layers of polarizing material. Explain how this pixel is able to control screen illumination. Draw the three layers of the pixel and label the flow of light.
Rasterization
- Below is a copy of the simple line drawing algorithm from class. What family of lines does it rasterize poorly?
void lineSimple(int x0,int y0,int x1,int y1,Color color) { int pix = color.getRGB(); int dx = x1 - x0; int dy = y1 - y0;
raster.setPixel(pix, x0, y0); if (dx != 0) { float m = (float) dy / (float) dx; float b = y0 - mx0; dx = (x1 > x0)? 1 : -1; while (x0 != x1) { x0 += dx; y0 = Math.round(mx0 + b); raster.setPixel(pix, x0, y0); } } }**
Bresenham’s line drawing algorithm improves the efficiency of the above code. Edit the code to eliminate the use of the round() function and to simplify the computation of mx0 + b* (use difference equation) in the while loop.
What’s a simple change you could make to lineSimple() so it worked for all lines (including those from answer )?
What is the definition of a concave polygon?
- In edge walking polygon rasterization, the algorithm moves across a scanline and performs a quick check to determine if each pixel is inside or outside the polygon. Explain how this checking works. In particular, consider the scan lines y and y’ below that intersect edges at their endpoints.
Clipping
When is it preferable to use Cohen-Sutherland line clipping?
In Liang-Barsky line clipping, we clip a line to four planes. If a line is parametrically defined by two points p 0 and p 1 : p(t) = p 0 + t(p 1 – p 0 ), and a plane is defined by a point q 0 and a normal N facing towards the outside, how do you solve for the point on the line that delineates the clipping boundary? Compute t.
y
y’
Viewing in 3-D
How is the homogeneous coordinate, (x, y, z, w) converted into an (x, y, z) tuple?
Given a camera position P , a vector normal to the image plane N , and an up vector Vup, describe how to convert a point W in world coordinates to a point in camera coordinates. You do not need to worry about translating the world origin to the camera position for this problem. For each of the axes of the camera’s coordinate system listed below, write the corresponding vector in world space. I’ve done one of the axes for you.
X:
Y:
Z: -N / ||N||
- What is a 4x4 viewing matrix M (^) ort that will transform homogeneous coordinates to points on the x-y plane at z = 0?
Color and Light
Define metamers.
Can a computer monitor produce all the colors we see in the world? Why or why not?
How would you select intensity values for each of 10 pixels arranged in a row so that the increase in brightness (from initial value of 0 to max of 99) looked smooth?
Define:
Hue:
Saturation:
Value:
- Write the equation we use to model the diffuse illumination of a surface?
I (^) d =
Given: an incoming light intensity, I a surface normal, N a vector from the surface to the light source, L a vector from the surface to the viewer’s eye, V specular constant, ks define the vector r from the image, in terms of these variables.
Define Mach banding, indicate the lighting model the frequently causes the effect, and describe why we perceive the effect.
