A short quiz on convolution and friends

Adrian F. Clark

  1. What is the effect of convolving an image with a +-shaped mask where the central pixel is -4 and its neighbours to north, south, east and west are 1?

  2. What is the effect of convolution with a 3 x 3 mask with each coefficient set to 1/9?

  3. The correlation coefficient between two images is a quantity that lies in the range -1 to +1. What does a value of -1 represent?

  4. What is the effect of convolution with the following mask? $$\frac19 \pmatrix{1 & 1 & 1\cr 1 & 1 & 1\cr 1 & 1 & 1\cr}$$

  5. What is the effect of convolving an image with a +-shaped mask?

  6. The Laplacean mask is useful for:

  7. What is the effect of convolving an image with the mask $$\pmatrix{0 & 1 & 0\cr 0 & 0 & 0\cr 0 & 0 & 0\cr}$$

  8. How does the time taken to perform a convolution vary with the dimension of a (square) mask?

  9. If a histogram has two visible peaks, where is the best place to set a threshold to isolate the corresponding regions?

  10. Why is simple thresholding not especially effective at locating light features in an image?

  11.