Digital image processing Flashcards
What is a digital image?
A digital image consists of pixel values that represent the intensity (of the light hitting that pixel when coming through the camera).
What factors determine a pixel’s brightness?
- Environment
Illumination and Reflectance, e.g. motion analysis, add reflective makers to the body to stand out and contrast against other objects within the room. They will have a high threshold and the camera can capture this.
- Camera Settings
You can alter the Aperture and Exposure to control brightness and thus will control or alter the brightness of pixel values.
What type of matrix is a Greyscale image?
A single Matrix.
Why is the Aperture and Exposure important within sport scenarios?
A larger Aperture means a larger hole in the camera to allow for a larger amount of light to come through means that there is a higher potential for blurring compared to a smaller hole. Therefore, it is quite hard to focus an opened Aperture compared to a more closed Aperture.
Therefore in a practical setting, If you can light the cameras field of view to be able to be able to close your paerture down to as small as possible your depth of field will be much further.
Regarding Exposure, if you have a fast moving object you will want to have a short exposure so that you do not get a blur effect.
Explain the meaning of this vector Di,j = | Ci,j - Bi,j |
Di,j = | Ci,j - Bi,j |
current frame(C) background frame(B) difference image(D)
The difference image is equal to or obtained by the vectors of the current frame minus the vectors of the background image. All in magnitude, in reference to its value not concerning positive or negative values.
To find the values of a particular pixel?
a(xx, xx)
e.g. a(100, 200).
Why and how do you apply a colourmap function on an image?
A colourmap is a three colour Matrix that specifies the red, green and blue content for a certain value.
Looking for a quick way to get the image pixel information.
impixelinfo, from there you’ll get X,Y and intensity values. You can also copy and paste it too.
What is the purpose of the image thresholding technique?
It is used in image analysis to partition an image into a foreground and background.
What are the foreground and background parts of an image?
Foreground: the part of a view that is nearest to the observer, especially in a picture or photograph.
Background: the part of a scene or picture that is farthest from the viewer : the part of a scene that is behind a main figure or object in a painting, photograph, etc. : a surface or color that is behind or around something (such as a printed design) : a position that attracts little attention.
Why do we use image thresholding?
We want to use image segmentation to isolate objects by converting grayscale images into binary images.
What type of image is most effective for image thresholding?
Images with high levels of contrast.
Define absolute difference.
Function for absolute difference (imabsdiff). So Z = imabsdiff(X,Y)
So it literally subtracts each element in array Y from the corresponding array X and will return the absolute difference in the corresponding element of the output array Z. So Z is where your get your absolute difference answer.
What is the sum of absolute differences in digital image processing.
SAD is a measure of the similarity between image blocks. This is calculated by taking the absolute difference between each pixel in the origional block and the corresponding pixel in the block being used for comparision.
What is the difference between a foreground and background image? And what would their matrices look like?
The foreground image is the portion of the frame that is closest to the camera. I am guessing that this is for example the closest objects towards the camera frame, e.g. when the object is in focus close to the camera frame this part of the image must be classified as the foreground image.
Whereas the background image is situated furthest away from the camera. In the image given you can identify and seperate the background and foreground images because the pixels taken on the shape of the foreground image, whilst the background image as it is a plain colour has consistent pixel values. Therefore, it is not the case that you can always identify as instant as this image, but you need to identify patterns in pixel values and relate colour values to the colours in the image.
