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# What is digital image processing?

Institute for Environmental and Spatial Analysis
University of North Georgia

## 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.

Figures from Gonzalez and Woods (2002)

## 2   Digital image processing

### 2.1   Human interaction & machine perception

“Processing digital images by means of a digital computer” (Gonzalez and Woods, 2002)

• 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 \ OutputImageDescription
ImageDigital Image ProcessingComputer Vision
DescriptionComputer GraphicsArtificial Intelligence

https://www.geeksforgeeks.org/digital-image-processing-basics/

• Computation of the average intensity
• Image compression

## 3   Early digital images

### 3.1   Digital image transfer

In 1921, this digital image in 5 gray levels was first sent across the Atlantic by submarine cable

1922

In 1929, 15 gray levels from London to New York

Figures from Gonzalez and Woods (2002)

### 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

Figures from Gonzalez and Woods (2002)

## 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

Figures from Gonzalez and Woods (2002)

### 5.2   Industrial inspection

• Automated inspection
• Cheaper
• Fast
• Reliable
Figures from Gonzalez and Woods (2002)

### 5.3   Law enforcement

• Vehicle plate recognition
• Fingerprint recognition
• Enhancement of CCTV images

Figures from Gonzalez and Woods (2002)

### 5.4   Human-computer interaction (HCI)

<cite(Image from )(Beyond Minority Report: Why William Gibson’s Neuromancer points to the future of UI)(https://www.techrepublic.com/article/beyond-minority-report-why-william-gibsons-neuromancer-points-to-the-future-of-ui/)>

### 5.5   Biometric authentication

<cite(Image from )(Hackers foil Samsung S8’s iris recognition technology using only a photo of an eye)(https://news.sky.com/story/hackers-foil-samsung-s8s-iris-recognition-technology-using-only-a-photo-of-an-eye-10890313)>

### 5.6   Remote sensing

• Manipulation of satellite imagery
• Terrain classification
• Landuse classification
• Soil moisture measurement
• Meteorology

### 5.7   NASA LANDSAT satellite bands

Band no.NameWavelength ($\mathrm{\mu m}$)Characteristics and use
1Visible blue0.45-0.52Maximum water penetration
2Visible green0.52-0.60Good for measuring plant vigor
3Visible red0.63-0.69Vegetation discrimination
4Near infrared0.76-0.90Biomass and shoreline mapping
5Middle infrared1.55-1.75Moisture content of soil and vegetation
6Thermal infrared10.4-12.5Soil moisture; thermal mapping
7Middle infrared2.08-2.35Mineral mapping
Tables from Gonzalez and Woods (2002)

### 5.8   NASA LANDSAT satellite images

Figures from Gonzalez and Woods (2002)