EECS 487 Winter 2003

Homework #2

Due February 16th
(Answers will be given During Review Lecture)

 

 

1.   Use the table in "Compositing Digital Images", Thomas Porter & Tom Duff and find the output pixel value for each operation in the table.

 

Argb	Aalpha
Three Pixels in Image A (Values not pre-multilied by alpha) 255,255,255 128,128,128 65,64,64	1.0 0.5 .25

 

Brgb	Balpha
Three Pixels in Image B (Values not pre-multilied by alpha) 128,128,128 128,128,128 128,128,128	1.0 0.5 0.25

 

                           Fa

                           Fb

                          AoverB =

                          BoverA =

                          A in B =

                          B in A =

                          A out B =

                          B out A =

                          A atop B =

                          B atop A =

                          A xor B =

 

2.   Up till now we talked about the output color value. What if we wanted to know the output alpha for A over B. How would you solve it and what is your answer.

 

 

3.   Suppose we want to draw a circle using a Bezier curve.  How many curve segments are necessary to get an accurate approximation of the circle?
       (use the 2D bezier cubic equation  in the notes to solve the following)

a)       Det ermine the control points for a 2 segment Bezier curve for a circle.

b)      Determine the mazimum error between the real circle r² = x² + y² and the bezier curve .

c)       Determine the control points for a four segment Bezier curve for a circle  and repeat step b.