What is digital image processing?
1 What is an image?
1.1 Mathematical representation
Two-dimensional function $f(x, y)$
- $x$ and $y$: Spatial coordinates
- $f$: Intensity or gray level of the image at $(x, y)$
1.2 Digital image
When $x$, $y$, and $f$ are finite and discrete.
Optionally, $t$ (time) for image sequences.
A representation of a two-dimensional image as a finite set of digital values called picture elements or pixels.
What is this?
1.3 Digitization
Digitization implies approximation.
2 Digital image processing
2.1 Human interaction & machine perception
“Processing digital images by means of a digital computer” (Gonzalez and Woods, 2002)
Focuses on two major tasks:
- Improvement of pictorial information for human interaction
- Processing of image data for storage, transmission, and representation for autonomous machine perception
2.2 Three types of computerized processes
Low-level: Image input $\rightarrow$ Image output
- Noise reduction
- Contrast enhancement
- Image sharpening
Mid-level: Image input $\rightarrow$ Image attributes
- Edges
- Contours
- Identity
Higher-level: “Making sense” of recognized objects
2.3 Image processing vs. image analysis
Image processing: Low- and mid-level processes
Image analysis or computer vision: Higher-level process
2.4 Fields of image processing
Typical categorization
Input \ Output | Image | Description |
---|---|---|
Image | Digital Image Processing | Computer Vision |
Description | Computer Graphics | Artificial Intelligence |
What about
- Computation of the average intensity
- Image compression
3 Early digital images
3.1 Digital image transfer
3.2 First picture of the moon by a spacecraft
The first picture of the moon by the NASA Ranger 7 spacecraft on July 31, 1964
4 Applications of digital image processing
- Image enhancement
- Industrial inspection
- Law enforcement
- Medical imaging
- Astronomy
- Object recognition
- Augmented reality
- Human-computer interaction (HCI)
- Processing of remote sensing imagery
- Etc.
5 Examples
5.1 Image enhancement
5.2 Industrial inspection
5.3 Law enforcement
5.4 Human-computer interaction (HCI)
5.5 Biometric authentication
5.6 Remote sensing
- Manipulation of satellite imagery
- Terrain classification
- Landuse classification
- Soil moisture measurement
- Meteorology
5.7 NASA Landsat satellite bands
Band no. | Name | Wavelength ($\mathrm{\mu m}$) | Characteristics and use |
---|---|---|---|
1 | Visible blue | 0.45-0.52 | Maximum water penetration |
2 | Visible green | 0.52-0.60 | Good for measuring plant vigor |
3 | Visible red | 0.63-0.69 | Vegetation discrimination |
4 | Near infrared | 0.76-0.90 | Biomass and shoreline mapping |
5 | Middle infrared | 1.55-1.75 | Moisture content of soil and vegetation |
6 | Thermal infrared | 10.4-12.5 | Soil moisture; thermal mapping |
7 | Middle infrared | 2.08-2.35 | Mineral mapping |