COM00009I Vision and Graphics 2019–20
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COM00009I
BEng, BSc, MEng and MMath Degree Examinations 2019–20
Department of Computer Science
Vision and Graphics
1 (20 marks)
(i) [5 marks] Consider images acquired by sensors sensitive to either ultraviolet or
infrared radiation. How can you visualise the information from such images?
(ii) [5 marks] What is a view volume in graphics? What would be atypical view volume for orthographic and for perspective projection systems?
(iii) [10 marks] For each of the following homogeneous transformation matrices, state whether the transformation acts on 2D or 3D points and describe the effect of the transformation.
(a) [2 marks]
(b) [2 marks]
(c) [2 marks]
(d) [2 marks]
(e) [2 marks]
2 (40 marks)
(i) [8 marks] A Charge-coupled Device (CCD) is one of the main technologies that can be used as an image sensor in a camera. With the aid of a diagram, describe how a CCD sensor can be used to build an image.
(ii) [4 marks] Two cameras CamA and CamB have signal to noise ratio (SNR) 25dBand 38dB respectively, which of the two cameras is preferable and why?
(iii) [8 marks] If the mean emission rate for an 8-bit CCD sensor is β photons per second overtime t, what expression can be used to compute the signal to noise ratio for its:
(a) [4 marks] Photon noise
(b) [4 marks] Quantisation noise
(iv) [8 marks] Consider a simple edge detection algorithm. List four challenges faced by simple edge detection algorithms in images. Briefly describe the reasons behind each of these challenge.
(v) [12 marks] Consider a pair of images viewing a cube from two directions, where each image plane is parallel with one of the visible faces of the cube.
(a) [5 marks] Redraw approximately the scene setting provided in the figure, indicating the epipolar lines and the epipolar points.
(b) [3 marks] If the scene consists of a cube and the image planes are parallel with two cube faces, as indicated in the figure above, what regions of the cube would be visible in each of the two images?
(c) [4 marks] Write the transformation matrix from Image 2 to Image 1 in homogeneous coordinates between the pair of views when each of their view plane normals VPN1 and VPN2 formangles of 45 degrees with the line joining their centres of projections COP1 and COP2. Consider the coordinate system as indicated in the figure, with the centre of the coordinate system located in COP1, where the plane of the observed point O, COP1 and COP2 is parallel with XZ plane, and assume that the distance between COP1 and COP2 island that the vector joining COP1 and COP2 is parallel to X axis.
3 (40 marks)
(i) [4 marks] Consider the image of a scene using graphics. How would you simulate the focus in your image?
(ii) [10 marks] Consider salt-and-pepper noise in a grey-level image, where each noise sample has the size of a pixel.
(a) [5 marks] Indicate the most suitable filter which will remove salt-and-pepper noise, from among those discussed in the lectures.
(b) [5 marks] What sort of side effects could occur in the image as the result of image filtering with the filter proposed at (a).
(iii) [6 marks] Briefly describe how are colours represented in the Munsel colour system?
(iv) [8 marks] Consider interpolation shading.
(a) [2 marks] Describe one advantage of Phong shading over Gouraud shading, e.g. describe a phenomena that Phong shading can correctly recreate that Gouraud cannot.
(b) [6 marks] Consider the Phong interpolation shading algorithm. Describe how a normal at a point inside a triangular face is computed from vertex normals when making a shading calculation.
(v) [4 marks] What is a "Lambertian" surface?
(vi) [8 marks] You wish to render an image in which the viewer is looking out of a train window. A reflection of a face is visible on the window and out of the window you can see a building. Consider using ray tracing.
(a) [4 marks] Draw a schematic diagram of the scene showing a ray for which
both the face and building are visible. You do not need to show shadow rays and only need trace rays that are necessary for the face and building to be visible. Label each object and each ray segment with a unique name.
(b) [4 marks] Draw the ray tree for the ray shown in your schematic. You should label each node in your tree with the object that is intersected by the incoming ray. Label edges with the label used in the schematic for the corresponding ray segment.
2024-01-09