Computer Science 455

Instructor: R. P. Burton

Third Quiz

February 19-20, 2008 

Name _________________________________________ Score ____________/39

1. A pixel mask, such as 10 pixels on and 5 pixels off, would be suitable (and uniform) for “texturing” line segments with arbitrary endpoints.

1. true
2. false

 

(b) 

2. When a curve is scan-converted for a raster device, the result is always a polyline.

1. true
2. false

 

(a) 

3. Soft fill provides

1. uniform surface color
2. a mixing with white light to achieve a pastel effect
3. a mixing with background color(s)
4. a hollow interior

 

(c) 

4. Which of the following is NOT a fill style?

1. solid
2. hollow
3. patterned
4. (all of these are fill styles)

 

(d) 

5. If the boundary is 4-connected, the fill style should be ___; if the boundary is 8-connected, the fill style should be ___.

1. 4, 4
2. 4, 8
3. 8,4
4. 8,8

 

(c) 

6. Boundary fill colors anything that is not boundary, whereas flood fill replaces an existing color.

1. true
2. false

 

(a) 

7. Either boundary fill or flood fill can use a 4 or 8 style, or can fill sections of scan lines (above and below).

1. true
2. false

 

(a) 

8. Filling sections of scan lines (above and below) requires convex polygons with no holes.

1. true
2. false

 

(b) 

9. Aliasing has been described as distortion of information due to a low sampling rate.

1. true
2. false

 

(a) 

10. Antialiasing does not actually solve the aliasing problem; it merely makes it less of a problem.

1. true
2. false

 

(a) 

11. Supersampling sometimes is called postfiltering, since intensities are computed and then combined.

1. true
2. false

 

(a) 

12. Which is likely to be a more accurate method for antialisaing?

1. supersampling with a 4x4 subpixel grid
2. area sampling
3. pixel phasing

 

(b) 

13. All of the following can be provided in software EXCEPT

1. supersampling
2. area sampling
3. pixel phasing
4. (no exceptions here)

 

(c) 

14. Antialiasing is achieved by

1. supersampling
2. area sampling
3. either supersampling or area sampling

 

(c) 

15. What is the function of bundled attributes?

1. to make sure that all attributes are specified
2. to provide an interpretation of all attributes for each output device
3. to provide compatible attributes

 

(b) 

16. Transformations used to achieve animation are likely to be referred to as

1. modeling transformations
2. geometric transformations

 

(b) 

17. Which of the following cannot be represented as a matrix operation?

1. 2D translation
2. 2D rotation
3. 2D scaling
4. (all can be represented as a matrix operation)

 

(d) 

18. Scaling affects

1. dimensions of shapes
2. offsets of shapes (relative to the origin, for example)
3. both dimensions and offsets

 

(c) 

19. In the context of transformations, what is the primary reason for using homogeneous coordinates?

1. To do transformations in 3, or even 4 dimensions
2. To accommodate translation, rotation, and scaling in a single n x n matrix
3. To accommodate output devices with different aspect ratios

 

(b) 

20. A point in 2D space maps uniquely to only one point in 3D homogeneous coordinate space.

1. true
2. false

 

(b) 

21. To invert a translation, rotation, or scaling matrix, simply invert each element of the matrix.

1. true
2. false

 

(b) 

22. Suppose M = ABCD, where A, B, C, and D are individual transformation matrices.  What is M^-1?

1. DCBA?
2. A^-1B^-1C^-1D^-1
3. D^-1C^-1B^-1A^-1
4. None of the above

 

(c) 

23. When three matrices are composed to provide rotation about an arbitrary point and the composed matrix is applied to the data describing the shape to be rotated, the arbitrary point is translated to the origin, the rotation occurs about the origin, and the arbitrary point is returned to its original position.

1. true
2. false

 

(b) 

 

24. Which matrix is adjacent to (“next to”) the original data for rotation about an arbitrary point?

1. the matrix taking the arbitrary point to the origin
2. the matrix containing the rotation angle
3. the matrix returning the arbitrary point to its original position
4. (it doesn’t matter)

 

(a) 

25. To realize the composite matrix described in the previous question, the values of ___ matrix elements need to be determined (assuming the operations are taking place in the xy-plane).

1. 3
2. 6
3. 9
4. 12

 

(b) 

26. Reflection can take place across any of the following except

1. a line not passing through the origin
2. a line not parallel to a principal axis
3. a point
4. (no exceptions here)

 

(d) 

27. In 2D, the x coordinate typically is sheared based on the ___ coordinate(s), and the y coordinate is sheared based in the ___ coordinate(s).

1. x, y
2. y, x
3. x or y, y or x

 

(b) 

28. To invert a shearing based on the y coordinate,

1. shear again based on the y coordinate, but with the negative of the shearing factor
2. shear again based on the y coordinate, but with the inverse of the shearing factor
3. shear again based on the x coordinate, but with the negative of the shearing factor
4. shear again based on the x coordinate, but with the inverse of the shearing factor
5. (none of these will invert the shearing)

 

(a) 

29. To do a “pix block transfer” (i.e. translation) start with a scan line containing

1. an overlapped corner of the source rectangle
2. an overlapped corner of the destination rectangle
3. an overlapped corner of the source rectangle and the destination rectangle
4. no corners

 

(a) 

30. Suppose the data is described relative to coordinate system A, but we would like to have it described relative to coordinate system B.  The appropriate transformation to apply to the data maps coordinate frame ____.

1. A onto coordinate frame B
2. B onto coordinate frame A

 

(b) 

31. An arbitrary composable matrix for 3D translation always has  ____ elements with the value of zero.

1. 3
2. 6
3. 9
4. 12
5. none of the above

 

(c) 

32. An arbitrary composable matrix for 3D scaling always has  ___ elements with the value of zero.

1. 3
2. 6
3. 9
4. 12
5. none of the above

 

(d) 

33. A arbitrary composable matrix for 3D rotation (about a principal axis) always has  ____ elements with the value of zero.

1. 3
2. 6
3. 9
4. 12
5. none of the above

 

(e) 

34. A arbitrary composed matrix representing translation, scaling, rotation, reflection, and shearing in 3D always has ____ elements with the value of zero.

1. no
2. 3
3. 6
4. 9
5. 12
6. none of the above

 

(b) 

35. Reflection in 3D can occur across any of the following EXCEPT

1. a line not passing through the origin
2. a line not parallel to a principal axis
3. a point
4. a plane
5. (no exceptions here)

 

(e) 

36. Shearing in 3D always is uniform in at least two dimensions.

1. true
2. false

 

(b) 

37. The x-axis points up, the y-axis points right, and the z axis points out.  Rotation is counterclockwise about the z-axis.  Where is the minus sign?

1. on the first row
2. on the second row
3. on the third row
4. can’t say in general

 

(b) 

38. To rotate about an arbitrary axis in 3D, how many matrices typically are composed?

1. 3
2. 5
3. 7
4. 8
5. 9 or more

 

(c) 

39. To transform from an arbitrary 3D coordinate system to another arbitrary 3D coordinate system, how many matrices are composed?

1. 2 or less
2. 3 or 4
3. 5 or 6
4. 7 or 8
5. 9 or more

 

(c)