Intensity Transformation & Spatial Filtering

1. Intensity Transformation and
Spatial Filtering
19.08.2020
1:30 pm

2. Intensity Transformations Functions
• Image Negatives
• Log Transformations
• Power Law (Gamma) Transformations
• Piecewise-Linear Transformation Functions
• Contrast Stretching
• Intensity-level slicing
• Bit-plane slicing

3. Introduction
• r= value of pixel before processing
• s=value of pixel after processing
• s=T(r)
• Stored in one dimensional array
• Mapping from r to s - table lookups
• 8 bit – 256 entries

4. Image Negatives
• [0, L-1]
• s=L – 1 - r
• Negative – reversing the intensity
level
• Enhancing white or gray embedded
in dark region

5. Log Transformations
• s=clog( 1 + r)
• Narrow range of low intensity
• Inverse Log transformation
• Compresses the dynamic range of
images with large variations
• Pixel value in Large range – Fourier
Spectrum.
• Intensity detail may lost in Fourier
Spectrum

6. Power Law
• Gamma Transformation
• s=crγ
• Measurable output
• Input is 0 s=c(r+ε) γ
• Issue of display calibration
• Identity transformation – c = ϒ = 1
• Gamma Correction

7. Power Law
• Simply intensity map
• Gamma correction – straightforward
• S=r
1
2
.
5
= r0.4
• Input to the monitor
• Same intensity