Lecture 4 pt 4 Flashcards
What is a Sinusoidal Grating?
A 2D representation in which the amplitude varies sinusoidally along a certain direction
What does Sinusoidal mean?
Having the form of a Sin wave
What are the parameters of a Sinusoidal Grating?
- Amplitude
- Wavelength / Frequency
- Orientation
- Phase
What does the amplitude parameter control in Sinusoidal Grating?
The amplitude, also known as contrast, determines the difference in grayscale values between the maximum and minimum points of a grating.
How does the amplitude affect the appearance of the sinusoidal grating?
In the grating with the highest amplitude, the peak of the grating is black and the trough is white.
When the grating is lower, the peak and trough start to blend into a similar grey
when the amplitude is 0, the entire image has the same graylevel.
How does wavelength / frequency affect the appearance of the sinusoidal grating?
The shorter the length of the wave, the more waves that fit into the same region of space, and so the frequency is higher.
Describe what the phase parameter is?
The phase parameter is essentially the starting point of where the waves start.
What is the Fourier Transform?
The Fourier Transform is a transformation that transforms a function into a form that describes the frequencies present in the original function.
What does a visual representation of the Fourier Transform look like in relation to the Sinusoidal Grating?
A representation of the Fourier Transform for a sinusoidal grating should show a value of 0 everywhere except for two points which will always be symmetrical to eachother.
the distance between the dots depends on the wave frequency.
The orientation of the dots should match the Sinusoidal Grating.
Name some Image Processing concepts that can utilize the Fourier Transform.
- Edge Detection
- Noise Reduction
- Blurring of image
- Feature Extractions
What is a low-pass filter?
A low-pass filter is a filter that passes signals with a frequency lower than a selected cutoff frequency and takes away signals with frequencies higher than the cutoff frequency.
What is a High-Pass filter?
The opposite of a low-pass filter, it’s a filter that passes signals with a frequency higher than a certain cutoff frequency and takes away signals with frequencies lower than the cutoff frequency.
What are the categories that components of the Fourier Transform can be divided into?
- Low frequency Components
- High frequency components
define the low-frequency components
low-frequency components are ones whose neighbouring pixels have similar brightness values
Define the high-frequency components
High-frequency components are ones whose neighbouring pixels have different brightness values.
(At edges or noise points)
