EE465: Introduction to Digital Image Processing1 Introduction to Grayscale and Color Images Image...

EE465: Introduction to Digital Image Processing 1

Introduction to Grayscale and Color Images

Image acquisitionLight and Electromagnetic spectrumCharge-Coupled Device (CCD) imaging and Bayer

Pattern (the most popular color-filter-array)Sampling and Quantization

Image representationSpatial resolutionBit-depth resolutionLocal neighborhoodBlock decomposition


Electromagnetic spectrum


Light: the Visible Spectrum

Visible range: 0.43µm(violet)-0.78µm(red)Six bands: violet, blue, green, yellow,

orange, redThe color of an object is determined by the

nature of the light reflected by the objectMonochromatic light (gray level)Three elements measuring chromatic light

Radiance, luminance and brightness


Sensor Array: CCD Imaging

Charge coupled device (CCD) image sensor


http://en.wikipedia.org/wiki/Charge-coupled_device


Complementary Metal Oxide Semiconductor (CMOS) Image Sensor


http://www.dalsa.com/corp/markets/CCD_vs_CMOS.aspx


Image Formation Model

f(x,y)=i(x,y)r(x,y)+n(x,y)

0<f(x,y)<∞

0<i(x,y)<∞

0<r(x,y)<1 reflectance

illumination

Intensity – proportional to energyradiated by a physical source

(“intrinsic images”)

n(x,y) noise


Sampling and Quantization: 1D Case


2D Sampling and Quantization


3D Visualization

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It is useful to take an analogy to rain gauge (image intensity valuesMeasure the amount of ``photon rain’’)

Color Imaging: Bayer Pattern


US3,971,065

http://en.wikipedia.org/wiki/Bayer_patternhttp://ask.metafilter.com/17138/3CCD-vs-1CCD

$38,990

$309

Demosaicing (CFA Interpolation)


Simple Ideas: Linear Interpolation


You will be asked to try these simple ideas in CA#2

Biological vs. Artificial Sensors


US3,971,065 Cone distribution in human retina

Question: Engineers’ invention vs. nature’s evolution, who wins?

Digital Single-Lens Reflection (DSLR) Cameras



Nikon D50


Kodak Easyshare

Photography 101

prosInterchangable lensGreater quality and

lower noiseSuitable for high-

motion and low-light environment

Better focusing capability

Larger focal length

ConsLarger and heavierMore expensiveLack of video modeSensor dust problemMore difficult to focus

on very close objects


The Plague in Photography: Motion Blur



High Dynamic Range Imaging

Q: Can we generate a HDR image (16bpp) by a standard camera?A: Yes, adjust the exposure and fuse multiple LDR images together


HDR Display (After Toner Mapping)

Note that any commercial display devices we see these days are NOT HDR



Beyond Visible

Gamma-ray and X-ray: medical and astronomical applications

Infrared (thermal imaging): near-infrared and far-infrared

Microwave imaging: Radio-frequency: MRI and astronomic

applications


Thermal Imaging

Pseudo-color representation(Human body dispersing

heat denoted by red)

Operate in infrared frequency

Grayscale representation(bright pixels correlate withhigh-temperature regions)


Low Signal-to-Noise (SNR) Behavior

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

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noise

signal


Radar Imaging

Mountains in Southeast Tibet

Operate in microwave frequency


Synthetic Aperture Radar (SAR)Environmental

monitoring, earth-resource mapping, and military systems

SAR imagery must be acquired in inclement weather and all-day-all-night.

SAR produces relatively fine azimuth resolution that differentiates it from other radars.


Magnetic Resonance Imaging (MRI)

knee spine head

Operate in radio frequency


Basic Principle of MRI

IFT

k-space


visible infrared radio

Comparison of Different Imaging Modalities


Fluorescence Microscopy Imaging

normal corn smut corn

Operate in ultraviolet frequency


What Does a Neuron Look Like?

Real imageArtistic illustration


X-ray Imaging

chest head

Operate in X-ray frequency


Positron Emission TomographyOperate in gamma-ray frequency

Mechanical Categorization of SensorsMotionless imaging

Sensor is kept still during the acquisition (e.g., CCD cameras)

Motion-aided imagingSensor moves along a line or rotates around a center

during the acquisition (e.g., document scanning and MRI scanning)

Subtle relationship between visual perception and motion“We move because we see; we see because we

move” – J. Gibson



Single-sensor Imaging


“Motion” Aids Imaging



Introduction to Grayscale ImagesImage acquisition

Light and Electromagnetic spectrumCharge-Coupled Device (CCD) imagingSampling and Quantization

Image representationSpatial resolutionBit-depth resolutionLocal neighborhoodBlock decomposition


Image Represented by a Matrix

Spatial resolution

Bit-depth resolution


Spatial Resolution


Image Resampling


Towards Gigapixel

Mega-pel Giga-pel

http://triton.tpd.tno.nl/gigazoom/Delft2.htm

Photographers and artists have manually or semi-automatically stitched hundreds of mega-pel pictures together to demonstrate how a giga-pel picture looks like the power of pixels


Aliasing in Digital Images


Bit-depth Resolution


Bit-depth Resolution (Con’d)


Commonly–used TerminologyCommonly–used Terminology

Neighbors of a pixel p=(i,j)

N4(p)={(i-1,j),(i+1,j),(i,j-1),(i,j+1)}N8(p)={(i-1,j),(i+1,j),(i,j-1),(i,j+1),(i-1,j-1),(i-1,j+1),(i+1,j-1),(i+1,j+1)}

Adjacency

4-adjacency: p,q are 4-adjacent if p is in the set N4(q)

8-adjacency: p,q are 8-adjacent if p is in the set N8(q)

Note that if p is in N4/8(q), then q must be also in N4/8(p)


Euclidean distance (2-norm)

D4 distance (city-block distance)

D8 distance (checkboard distance)

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Common Distance Definitions


Block-based Processing

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