Course Outline 8/27/2009. SGN-3016 Digital Image Processing (5 cr)

Transcription

1 SGN-3016 Digital Image Processing (5 cr) Lecturer: Moncef Gabbouj Lectures: Period I, Room TB 110, Mondays Periods II, Room TB 219, Mondays 14: Exercises and Assistants: Dr. Esin Guldogan (Office TC 413) Group 1: Thursdays , room TC 415 Group 2: Fridays , room TC 415 Course webpage: First Lecture: Monday 7 September 2009 First Exercise: Thursday 17 th September 2009 (Group 1), and Friday 18 th September 2009 (Group 2) Description: Basic principles and concepts of image processing will be covered in the course. Textbook: Rafael C. Gonzalez and Richard E. Woods, Digital Image Processing, Third Edition, Prentice Hall, 2007, Chapters 1-6. Other references: The Image Processing Handbook, John C. Russ, Editor, CRC Press, Introduction to Digital Image Processing with Matlab, A. McAndrew, Thomson, Course Outline to Digital Image Processing Chapter 2: Digital Image Fundamentals Chapter 3: Intensity Transformations and Spatial Filtering Chapter 4: Filtering in the Frequency Domain Chapter 5: Image Restoration and Reconstruction Chapter 6: Color Image Processing Chapter 8: Image Compression Chapter 10: Image Segmentation Early stages of digital photography over 85-year old!

2 Radiation-based images Images based on radiation from ElectroMagnetic spectrum are most familiar, e.g. X-ray images and visible spectrum images. EM waves can be thought of as propagating sinusoidal waves of varying wavelengths or as a stream of massless particles, each traveling in a wavelike pattern and moving at the speed of light. FIGURE 1.4 The first picture of the moon by a US spacecraft. Ranger 7 took this image on July 31, 1964, about 17 minutes before impacting the lunar surface (Courtesy of NASA) Each massless particle contains a certain amount (or bundle) of energy. Each bundle of energy is called a photon. If spectral bands are grouped according to energy per photon, we obtain the spectrum below Radiation-based images Each massless particle contains a certain amount (or bundle) of energy. Each bundle of energy is called a photon. If spectral bands are grouped according to energy per photon, we obtain the spectrum below. Examples of Gamma-ray imaging Bone Scan PET Scan notice the tumor in the brain and in the lung Cygnus loop is a gas cloud generated by a start in the constellation of Cygnus Gamma radiation from a valve in a nuclear reactor notice the area of 1.10 strong radiation Center for Gamma-Ray Imaging, Univ of Arizona: 2

3 Examples of X-ray imaging Chest X-ray X-ray of circuit board Image of blood vessels (angiogram) Computerised axial tomography (CT) of the head Cygnus loop in the X-ray band Examples of X-ray imaging Examples of ultraviolet imaging CT scan vs MRI imaging: Normal corn UV imaging is used in lithography, industrial inspection, microscopy, biological imaging and astronomical observations UV is used in fluorescence microscopy, a method to study material which can be made to fluoresce. Infected corn (by smut) Smut corn disease Cygnus loop in the UV band

4 Imaging in the visible and IR bands Examples of light microscopy images Applications range from enhancement to NASA s Landsat satellite captures and transmits images of Earth from space for the purpose of monitoring environmental conditions on the planet. It uses both visible and infrared regions of the spectrum. measurements More hurricane pictures from Plymouth State University Weather Center The Potomac river is clearly seen in all bands

5 Human settlements in the Americas

6 Examples of Scanning Electron Microscope (SEM) images

7 Photographs from Sharjah Examples of computer generated images 1.27 Photographs from Tampere

8 How are pictures made? A basic image capture system contains a lens and a detector. Film detects far more visual information than is possible with a digital system. With digital photography, the detector is a solid state image sensor called a charge coupled device, (CCD) for short. On an area array CCD, a matrix of hundreds of thousands of microscopic photocells creates pixels by sensing the light intensity of small portions of the film image Ref.: Types of Image Degradations (1/2) Types of Image Degradations (2/2) lack of contrast image enhancement BLURRING image enhancement motion blur NOISE image restoration 1.33 image restoration

9 Analog versus digital image processing Analog image Digital image + imitates light intensity - records only samples of the information rather than all of it + compactness + copy quality + scalability + freedom from noise + seamlessness + computer compatibility Recall that an analog signal copies by imitating: Light from the camcorder lens slams into a sensor on the imaging chip, creating an electrical charge. The stronger the light, the stronger the charge, which is to say that the electrical signal is imitating the intensity of the light that produced it. Multiply this stimulus/response by several hundred thousand sensors covering all three primary colors and you have the entire optical image imitated by an electrical signal of rapidly and continuously varying voltage In a digital system, by contrast, the first thing that happens to the original continuous signal is that it's fed through an analog/digital converter chip. That chip looks at the signal hundreds of thousands of separate times per second and assigns each discrete sampling a numerical value that corresponds to the strength of the signal at that precise moment in time. These numbers, rather than the signal itself, represent the digital image. This means that digital recording differs from analog in two crucial ways: It numerically encodes the information rather than electrically mimicking it It records only samples of the information rather than all of it. Compactness Information in analog image or video can be stored very efficiently and cheaply (up to two and a half hours of video on one $1 VHS tape at SP speed). High-quality digital video demands a huge amounts of storage space. For example, DVDs (Digital Versatile Disks), must squeeze 4.7 gigabytes of data onto a single side of the disk just to fit a feature-length movie and that's with a hefty dose of compression

10 Scalability All video, analog and digital, tends to look sharper and clearer on a smaller screen; it's the natural result of squeezing the same amount of visual information into a smaller space. All but the highest quality digital video, however, suffers greatly from enlargement. When you blow up your digitized image onto a huge home-theater TV screen, for example, all of those invisible digital compression artifacts become quite noticeable--straight lines become jaggy, curves look blocky, etc. Analog video, on the other hand, is much better at filling larger screens with sharp-looking images. Seamlessness In the audio world, some purists have returned to analog (vinyl LP) recordings because they hear the fact that digital recordings only sample the signal at intervals instead of copying the whole thing. To them, CDs sound hollow and brittle as a consequence Copy Quality We talk about "copying" a digital image or a digital video file, but we are not actually making a copy at all. Instead, we're making a transcription: rewriting the information rather than duplicating it. Instead of copying the video signal, digital duplication transcribes the numerical code that describes that signal. If you transcribe it accurately, you can decode the result into a daughter signal that is essentially indistinguishable from the parent Freedom from Noise Noise is any disturbance in an electrical current that is not part of the signal, and every current carries a certain amount of this electrical garbage. Since an analog dupe is an imitation, it happily copies the noise along with the parent signal, while adding new noise in the process. That means that in each generation, the noise level relative to the signal (signal-to-noise ratio) increases and the quality decreases proportionately. In digital recording, noise is not a problem because the signal consists entirely of current pulses carrying information e.g. Morse code: power on = 1; power off = 0. If the voltage level of the "power on" part of the signal is well above the noise level, then the transcribing system can be set to respond only to current at that level and ignore the noise entirely. So even if the process adds a small amount of its own noise, it never copies the parental noise--nor does it pass on its own noise to the copy. The result is that digital video can be copied through many generations without appreciable quality loss. This is a massive improvement over analog video

11 Computer Compatibility By far the biggest advantage of digital video is that a computer can process and store it. For many years, professionals have digitized video, not only to take advantage of loss-free duplicating, but also to perform image editing. Image editing means superimposing titles, compositing multiple images, and adding effects like dissolves and wipes. But as hard drives got bigger and faster, and as image compression techniques improved, it became possible to digitize the signal and then keep it in that form indefinitely by storing it in the computer. Digital storage also saw the birth of nonlinear editing, with almost instant access to any footage anywhere in the computer. This advantage is so great that digital video would probably prevail over analog due to random (nonlinear) access alone