# A short quiz on convolution and friends

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

• the image is unchanged
• the image is blurred
• the image is shifted up one pixel
• the image is shifted down one pixel

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

• +-shaped features will be enhanced

• dark spots will be enhanced
• light spots will be enhanced
• X-shaped features will be enhanced
3. Why is simple thresholding not especially effective at locating light features in an image?

• changes in illumination change the lightness of features

• thresholding is a local operation
• thresholds are difficult to determine
• thresholding is a global operation
4. What is the effect of convolving an image with the mask $$\pmatrix{0 & 1 & 0\cr 1 & 1 & 1\cr 0 & 1 & 0\cr}$$

• X-shaped features will be enhanced
• dark spots will be enhanced
• light spots will be enhanced
• +-shaped features will be enhanced

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

• below the lower peak
• mid-way between the peaks

• at the top of the upper peak
• above the upper peak
6. 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?

• X-shaped features will be enhanced
• the image will be lightened
• +-shaped features will be enhanced
• dark and light spots will be enhanced

7. What is the effect of convolving an image with the mask $$\pmatrix{0 & 1 & 0\cr 1 & -4 & 1\cr 0 & 1 & 0\cr}$$

• X-shaped features will be enhanced
• +-shaped features will be enhanced
• dark spots will be enhanced

• light spots will be enhanced
8. The Laplacean mask is useful for:

• locating dark regions
• locating isolated white pixels

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

• it has no effect
• it will enhance edges
• it will detect isolated points
• it will blur edges

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

• it will enhance edges
• it will blur edges

• it has no effect
• it will detect isolated points
11.