Lecture 4 Flashcards
Define Image Enhancement
The process that improves the quality of the image for a specific application.
What are the main types of image enhancement methods?
3 main methods:
1. Spatial Domain Methods
2. Frequency Domain Methods
3. Combinations Methods
Define what spatial domain methods are
Spatial domain mathods are types of image enhancement methods.
Based on the direct manipulation of pixels in the image
Define what Frequency Domain Methods are
Frequency domain methods are a type of image enhancement methods.
Based on the modification of the fourier transform of the image
What are combinations methods
Combination methods are types of image enhancement methods.
Based on the combination of frequency domain methods and spatial domain methods.
How do you compute the brightness of a grayscale image?
Grayscale image brightness is found by getting the average intensity of all pixels in the image.
What is Exposure?
Exposure is the amount of light that enters the lens.
There are 3 types of exposure:
1. Overexposure
2. Underexposure
3. Long Exposure
What is Long Exposure?
Long exposure is a technique that captures a subject over an extended period of time
What is the difference between brightness and exposure?
Exposure is the amount of light that enters the lens of the camera, while brightness is how bright an object appears in the picture.
- Exposure is a property of the camera, while brightness is a property of exposure
What is Image contrast?
Image Contrast is the measure of the difference between the maximum and minimum pixel intensities of an image / The variation between the light and dark areas of a photo.
What is High Dynamic Range (HDR)?
HDR is a technique that produces images with a greater dynamic range of luminosity than standard dynamic range (SDR)
What is Dynamic Range?
The range of the lightest tones to the darkest tones in an image
What is wide dynamic range?
where both dimly and brightly lit areas are present in the field of view. The human eye is capable of wide-dynamic range.
How does one achieve HDR?
Use photos of the same scene with different exposure values and then combine the values
What is tonemapping?
A way of obtaining HDR. After the HDR image values have been merged, the photo has to be converted back to 8-bit to view it on usual displays
What are the three main types of Image Operations?
There are 3 main types of image operations:
1. Point Operations
2. Local Operations
3. Global Operations
What are point operations?
A point operation is an image operation where the output value of a coordinate is dependent only on the input value at the same coordinate.
They change a pixels intensity value according to some function F.
Pixel intensity depends on the input pixels intensity and the mapping function F
What are local operations?
A local operation is an image operation where the output value of a coordinate is dependent on the input values in the neighborhood of the same coordinate.
What are Global Operations
A global operation is an image operations where the output value of a given coordinate is dependent on all the values of the input image.
What are the different types of point operations?
4 main types of point operations:
1. Addition (changes Brightness)
2. Multiplication (Stretches/shrinks image contrast range)
3. Global thresholding
4. Gamma correction
What is an Image negative?
An image negative is produced by subtracting each pixel from the maximum intensity value.
e.g. For an 8-bit image, the max intensity value is 2^8 - 1 = 255.
So each pixel is subtracted from 255 to produce the output image negative.
What is Gamma Correction?
Gamma Correction is a type of point operation that can be used to correct the brightness of an image by using a non linear transformation between the input values and the mapped output values.
If in the operation the Gamma variable is less than 1, the image will appear lighter and darker otherwise. If the Gamma variable = 1 then the image brightness will remain the same.
What is Histogram Equalisation?
A technique used for adjusting image intensities to enhance image contrast.
The operation stretches dense parts of the histogram, where contrast is low, and condenses sparse parts of the histogram where contrast is high.
