Lecture Notes

What is Digital Image Processing?

Image - a 2D function f(x,y) where x and y represent the coordinates. f would be the amplitude for the given coordinates x and y.

NOTE: the 2D function f(x,y) (amplitude) is called the intensity/gray level of the image.

An image is considered a digital image when x, y, and intensity of values are all finite and discrete.

NOTE: for an analog image: x, y, and intensity of values are continuous.

For digital images, digitation will make digital images as approximations–representation of continous values are converted to be digital.

Common formats for digital images:

  1. Grayscale - 1 value per pixel (Black and White). Value goes from 0-255. 1-tuple. Grayscale has 1 grid.
  2. Binary - 1-bit depth: each pixel can either be 0 or 1 (0 for black, 1 for white)
  3. RGB - 24-bit depth: 8 bits per channel. 3 values per pixel (R, G, B). Each value goes from 0-255. 3-tuple. RGB has 3 grids.

(8b, 8b, 8b) = 0 - 255 (256bits in total or 3 bytes) 256 ^ 3 bits

  1. RGBA - 48-bit depth: 16 bits per channel. 3 values per pixel (R, G, B, Alpha/Opacity). Each value goes from 0-255. 3-tuple RGBA has 3 grids.

(16b, 16b, 16b) = 0 - 65,535 (65,536 bits in total) 65,536 ^ 3 bits

Digital Image Processing - The process of using an algorithm to perform processing on digital images.

A pixel is the smallest element in a digital image–each pixel carries information about the color and intensity.

The image size refers to the number of pixels in an image.

JPEG - lossy compression (reduces file size and quality is lost) PNG - lossless compression (preserves quality but file size is larger than JPEG) TIFF -lossless compression and uncompressed formats (file size varies)

Origin of Digital Image Processing: Submarine cable used in the early 1920s to transmit pictures between London to New York.

The Bartlane Cable Picture Transmission System reduced the amount of time it took to transmit a picture across the Atlantic from over a week to less than 3 hours.

in 1929, gray scale levels for code images went from 5 levels to 15 levels.

Diverse Appliations of Images:

  1. Electromagnetic
  2. Acoustic - Soundwaves to create image
  3. Ultrasonic - Subset of accoustic. Has a higher frequency than accoustic
  4. Electronic - Sensors capture images
  5. Synthetic/Generated - VR, Computer Models, animation

Chapter 1 Reading

Digital Image Processing is important because:

  1. Improving pictorial information for human interpretation
  2. Processing image data for tasks such as storage, transmission, and extraction of pictorial information.

Image is defined as a 2D function f(x,y) where x and y are spatial coordinates.

Intensity/gray level - Ampliude of f of any pair of coordinates.

Digital Image - If x, y, and intensity of values of f are all finite and discrete.

Digital Image Processing - Processing digital images by means of a digital computer. It is composed of finite number of pixels.

Pixel - elements of a digital image.

Three computerized-level processes to consider

  1. low - primitive operations (image preprocessing). ex: reduce noise, contrast enhancement, and image sharpening. Both input and output are images.
  2. mid - uses segmentation to reduce objects to a suitable form of computer processing and classification. Inputs are generally images; however, outputs are attributes extracted from those images (ex: edges, contours).
  3. high - involves making sense of recognized objects (image analysis) and performing cognitive functions normally associated with human vision.

Tomography - Ring of detectors would encircle an object and the source (typically an X-Ray) would rotate around the object.

NOTE: Tomography would use algorithms that use the sensed data to make an image that would represent the sliced object. Basically you piece the slices together to form a 3D object.

Type of Source Images

The modern principal energy source for images today is the electromagnetic energy spectrum. Other sources of energy include:

  • accoustic
  • ultrasonic
  • electronic (electron beams)

For images that are created from the EM spectrum, EM waves can be conceptualized as propagating waves of varying wavelengths or stream of massless particles where each are traveling in a wavelike pattern that moves at a speed of light.

NOTE: Each massless particple contains a certain bundle of energy (photon).

Gamma-Ray Imaging

Gamma-Ray Imaging requires the presence of a radioactive isotope that emmits gamma rays as it decays. By doing so, images are produced via emissions collected by gamma-ray detectors.

Scenarios:

  1. Performing Bone Scans
  2. Positon Emission Tomography - Patient is injected with a radioactive isotope where it emits positrons as it decays.
  3. A star in the constellation

X-Ray Imaging

X-rays for medical and industrial imaging are generated via an X-ray tube (vacuum tube w/ cathode and anode) where electrons strike a nucleus, where then X-rays are released.

Intensity of X-rays are modified by absorption via a film sensitive to X-ray energy.

IMPORTANT: IN DIGITAL RADIOGRAPHY, DIGITAL IMAGES ARE OBTAINED BY USING TWO METHODS

  1. Digitizing X-ray films
  2. X-rays pass through the patient directly onto devices (phosphor screen)

Angiography - Form of radiography that obtain images of blood cells.

Computerized Axial Tomography (CAT) - Type of tomography that uses slices to create a 3D object in the form of an image.

Scenarios:

  1. Medical diagnostics
  2. Industry (astronomy)

Ultraviolet Imaging

UV Imaging is used in fluorescence microscopy–UV light is directed on the mineral fluorspar floresces to make the light visible.

NOTE: This is due to the fact that when UV radiation collides w/ an electron in an atom of a fluorescent material, the electron elevates to a higher energy level. Once the electron goes to the lower level, light is emitted as a photon in the visible (red) light region.

Visible and Infrared Band Imaging

Microwave Imaging

Radar is the principal application of microwave imaging.

Benefits of using microwave imaging is the ability to collect data over any region at any givne time, regardless of weather and ambient lighting conditions.

How an imaging radar works: Radar will illuminate an area (via micowave pulses) then a radar will use an antenna and digital computer processing to record the image. The image seen is the result of microwave energy being reflected back toward the radar antenna.

Radio Imaging

In medicine, radio waves are used in MRI scans.

NOTE: In MRI Scans, a powerful magnet and radio waves go through an individual’s body in short pulses. Each pulse will have a responding pulse of radio waves be emitted by the patient’s tissues.

Scenarios:

  1. Medicine
  2. Astronomy

Components to Digital Image Processing

Summary

Image - a 2D function f, that has two coordinates x and y that serves as the amplitude for the given coordinates.

Digital Image - x, y, and intensity values are all finite and discrete. Analog Image - x, y, and intensity values are continuous

Digitation - making digital images as approximations. mapping of continous values to digital.

Formats of digital images:

  1. Grayscale - 1 value per pixel that has values from 0-255
  2. Binary - 1-bit depth; pixel outputs 1 or 0 (0-black, 1-white)
  3. RGB - 24-bit depth; 8 bits per channel; 3-tuple; 3 values per pixel (r,g,b); each value goes from 0-255; 256 ^ 3 total bits = 16,777,216 possible colors
  4. RGBA - 48-bit depth; 16 bits per channel; 3-tuple; 4 values per pixel (r,g,b,a); each value goes from 0-65,535; 65,536^3 total bits = 65,536^3 possible colors

Digital Image Processing - use of algorithms to perform processing on digital images

Image Size - total number of pixels in an image

  • JPEG - lossy compression where file size and quality is lost
  • PNG - lossless compression where quality is preserved but file size is bigger than JPEG
  • TIFF - lossless compression and uncompressed formats (file size varries)

NOTE: order from least to worst is JPG, PNG, TIFF

The first use of digital image processing started in the early 1920s–pictures sent from London to New York.

Diverse Applications of Images:

  1. Electro
  2. Accoustic (sound)
  3. Ultrasonic (higher freq sound)
  4. Electronic (sensor)
  5. Synthetic/Generated (artificial)