Image Manipulation Flashcards

Question

Median Filter

Answer 1

A type of non-linear filter Sorts the pixel values in a given neighbourhood and then sorts them to find the median of these values. This median is used to replace the original pixel value in the outputted image. performs well with images that contains salt and pepper noise. As window size increases, median gets closer to local mean causeing more smearing and edge distortion

Answer 2

A type of local, non-linear, edge-preserving, noise-reducing filter. Similar to Gaussian Convolution, this filter is defined as a weighted average of pixels, except it also considers the variation of intensities to preserve edges. Two pixels are close together in bilateral filtering iff: 1. they occupy nearby spatial locations 2. Have a similar intensity value Controlled by two parameters: Spatial Parameter Range Parameter

Answer 3

Gaussian filters are local, linear filters while Bilateral Filters are local, Non-linear filters. Also, Gaussian filters use a Gaussian function that determines the weight of the pixels in the neighbourhood based on their spatial distance alone, while Bilateral Filters use Gaussian functions to determine the weight of the neighborhood pixels based on their spatial distance as well as their individual intensity values

Answer 4

The process is simplified to a multiplication, while in spatial domain filtering it is a convolution. Gives you control over the whole image simpler and computationally cheaper

Answer 5

Used to convert an image to the frequency domain the concept behind the fourier transform is that any waveform can be constructed using the sum of the sin and cos waves of different frequencies Amplitude = maximum value of the sin function Phase = the relative position of a wave with respect to one where y(0) = 0

Answer 6

FIltering --> low-pass filtering is commonly used to improve the performance of an edge detector with respect to noise Enhancement --> Emphasizes pixels where there is a significant change in the local intensity values. Performed by computing the gradient magnitude Detection --> indicates that an edge is present near a pixel in an image

Answer 7

Mathematical specification of shape and appearance. e.g. A 3D object might be described as a set of ordered 3D points along with some interpolation rule to connect the points and a reflection model to describe how light interacts with the object

Answer 8

the creation of shaded images from 3D computer models. involves considering how each object contributes to each pixel. Two ways: Object-Order Rendering --> For each object, all pixels that it influences are found and updated Image-Order Rendering --> For each pixel all the objects that influence it are found and the pixel value is computed. (Uses Ray tracing algorithm)

Answer 9

The creation of the illusion of motion through sequences of images

Answer 10

An image-order algorithm used for making renderings of 3D shapes. 1. Computes one pixel at a time. Each pixel has am "eye ray". 2. The "eye rays" are traced into the scene from the view point to the pixel, and tested for intersections with any objects in the scene. If the eye ray intersects any object, this intersection point is recorded. 3. Ray tracing algorithm then determines the pixel colour and how the surface at that intersection point interacts with light. (shading computation renders shadows, light and refractions).

Answer 11

Used to capture the process of light reflection. 3 variables in light reflection: 1. Light Direction --> Unit vector pointing towards light source 2. View Direction --> Unit vector pointing towards the camera. 3. Surface normal --> Unit vector perpendicular to the surface at the point where reflection is occurring 3. Surface normal

Answer 12

1. Lambertian --> amount of energy from a light source that falls on an area of a surface depends on the angle of the surface to the light Used for objects that aren't shiny (e.g. wood) Lamber's cosine law --> illumination is proportional to the cos of the angle between the surface and the light source View independent --> surface colour doesn't depend on the direction from which you look at. Appears matte.

Answer 13

View dependent shading model Aims to produce reflection that is at its brightest when view direction and light direction are symmetrically positioned across the surface normal. (Mirror reflection)

Answer 14

By comparing the half vector h (bisector of the angel between the view direction and the light direction) to the surface normal This is done by summing vector v and l and dividing the result by it's magnitude . If it is near the surface normal, the specular component should be bright. Otherwise it is dim. Achieved by computing the dot product between h and n, then taking the result of this to the power of the Phong exponent

Answer 15

Controls the apparent shininess of the surface normal