4-1 Flashcards
(16 cards)
purpose of image enhancement
to improve the interpretability or perception of information in images for human viewers, or to provide `better’ input for other automated image processing techniques
what is image enhancement
process of adjusting digital images so that the results are more suitable for display or further image analysis. For example, you can remove noise, sharpen, or brighten an image, making it easier to identify key features.
what are the 2 image enhancement categories
Spatial domain methods
Frequency domain methods
what is spatial domain method in image enhancement
Manipulate the image pixel value in spatial domain based on distribution statistics of the entire image or local region. Technique are based on direct manipulation of pixels in an image. eg. Mean Filtering, Medial Filtering
what is frequency domain method in image enhancement
Manipulate information in the frequency domain Technique are based on modifying the Fourier Transform of an image
s = T(r)
T is the transformation that maps a pixel value r into pixel value s
three types of transformation in Gray Level Transformation
- Linear (identity transform &
inverse transform) - Logarithmic
- Power-law
Linear Identity Transformation in Greyscale T. (2)
- Output intensities are identical to input intensities
- Does not have any effect on image. But added to the previous graph for completeness
also think of the image
Linear Inverse Transformation in Greyscale T. (3)
- is the opposite of identity transformation. Each value of the input image is subtracted from L-1 and then it is mapped onto the output image.
- Reverses the gray level order ie light areas appear dark & vice versa
- Suitable for enhancing white or gray details
embedded in dark regions esp when dark areas are dominant
S = T(r) = (L-1)-r
inv. trans
L number of gray levels
Logarithmic Transformation in Greyscale T.
Log Transformation expands values of dark pixels in image while compressing the lighter pixels.
Logarithmic Transformation in Greyscale T. effects and uses
Effects: Maps a narrow range of low pixel levels into wider range of output values. The opposite is true for the higher input values
Uses: particularly useful when the input pixel values may have an extremely large range of values. Suitable for compressing dynamic display on devices.
s = T(r) = c log(1+r)
log. trans
c is a constant & r >= 0
Inverse Logarithmic Transformation in Greyscale T. (2)
- Does the opposite of log transform
- Used to expand high pixel values while compressing the darker level values.
Power (Gamma) Transformation in Greyscale T. effect
Maps a narrow range of dark
input values into a wider range of output values and vice versa. More precise than log
s = T(r) = c r
power trans
c & (gamma) are +ve constant
