Point Processes / Intensity Transforms Flashcards
What is process of an intensity transform?
Taking a source pixel and applying some change or formula to create a target pixel.
In intensity transforms what does the target pixel depend on?
Only the source pixel and maybe some parameters
What are two common point processes?
Multiplication by a constant, addition of a constant
In the point process equation g(x,y) = a.f(x,y) + b , what are g,f,a,b?
f = original image
g = new image
a = gain (controls contrast)
b = bias (controls brightness)
In point processing, what does gain control?
Contrast, range of values increases and thus so does gaps between values
In point processing, what does bias control?
Brightness
An image is described as f(x,y), what is f?
An intensity value for each location / pixel ranging from 0 to a maximum e.g. 255
What is the equation for image negation?
G(x,y) = fmin + (fmax - f(x,y))
Explain the equation for negation.
f(x,y) is made negative then balanced back to the same range by adding fmin and fmax
What does negation do?
‘swap brightest values for darkest values’
What is dynamic range?
changing the range of intensity values of a digital image using intensity transforms
What is contrast stretching?
Converting a source image where intensities range from an initial min to max, to a new image with new min and max intensities
What is thresholding?
The simplest form of image segmentation, might be used to highlight grey image
What kind of transforming does thresholding use?
Non-linear transform using a threshold value, k, where anything below k is set to one low value (e.g. 0), and anything above k is set to one high value (e.g. 255/ white)
What is grey - level slicing?
Highlights a specific range of intensities. Everything in a specific range is converted to one value. Then other values are set to a low level or left at their original values.
What does gamma correction allow you to do as a technique?
A technique allowing you to display an image on a screen (to generate a displayable voltage)
Is gamma correction linear or non-lienar?
Non-linear
How is the gamma correction equation typically written?
g(x,y) = f(x,y)gamma
How do point processes operate on an image?
On each pixel independently, unaffected by surrounded pixel
What do linear processes do?
Change the appearance of a whole image
What can non-linear processes do that linear processes can’t?
Differentiate and distinguish objects/regions of an image
