What does Otsu's method do?

- maximizes the within-class variance
- minimizes the background variance
minimizes the within-class variance

- maximizes the background variance

Which of the following is not a valid equation for a straight line?

- the equation $x = m y - c$
the equation $y = m + x - c$

- the equation $y = c + x / m$
- the equation $x cos A + y sin A = r$

What does one do with the Hough accumulator to find lines?

- Each corner in the accumulator is a line in the image
- Each line in the accumulator is a line in the image
Each peak in the accumulator is a line in the image

- Each 3 x 3 region in the accumulator is a line in the image

Which of the following is a sensible region descriptor?

- the colour of the region's background
- the value of the centre pixel of a region
the circularity of a region

- the location of a region within an image

Why is a recursive region labelling algorithm poor in practice?

- it tends to overflow the computer's heap
- it is difficult to program
- it is too slow
it tends to overflow the computer's stack

If a histogram has two peaks, where is the best place to put a threshold to separate foreground from background?

- half-way up the higher peak
- at the lower peak
in the bottom of the dip between the two peaks

- half-way down the lower peak
- at the higher peak

What is the purpose of the Hough transform?

- To find edges in images
- To calculate an accumulator array
- To join together edges in images
To find the parameters of lines, etc

In the parametric Hough transform, what is the accumulator array indexed by?

- end-points
- gradient and intercept
- gradient magnitude and direction
radius and angle

What shape is the curve drawn in the parametric accumulator array from a single pixel in an image?

- a straight line
- an $x^2$ shape
- a $1/x$ shape
a sinusoid

How many lines are drawn in the parametric accumulator array from a single pixel in an image?

as many as there are angle entries in the accumulator array

- 1
- as many as there are radius entries in the accumulator array
- 360