Digital Imaging Study

2/17/10 Copyright © Nick D. Barzelay, 2006. All rights reserved. 1

Image Processing - A SurveyNick D. Barzelay

Rochester Institute of Technology

Summer, 2006


ContentsI. The ImageII. Working With ImagesIII. Image EvaluationIV. Image CorrectionV. ToolsReferencesImage Gallery


I. The Image

Faithful, distorted, and obscuredreal world representations


What We See Visible Electromagnetic Spectrum:

– 400 nanometers (approximate blue)– 700 nanometers (approximate red)

Levels of Brightness - 256– Human eye can only distinguish a portion– Inkjet or Laser can only print a portion

Gray Levels - 256– Human eye can only distinguish 20 to 30


Color Requirements

– Object– Light Source– Observer

Color Gradations– Hue - color as described by wave length– Saturation - amount of color present– Lightness

Amount of light Distinction between dark and light

Color Types– Additive - light emitting (RGB)– Subtractive - light reflecting (CMY)


Perspective Depth Perception comes from:

– Human Stereoscopy– Relative Size– Precedence– Perspective– Atmospheric Haze– Other Clues

Viewing Geometry– Spatial Area or Distance– Angles– Time


II. Working With ImagesPurpose

AcquisitionProcessingApplication


Image Acquisition Continuous Tone Subject - Selected subject material

for black & whites or color Sampling (continuous tone color or gray scale)

– Digital Camera or Scanner– Collect analog samples in a Sampling Grid (pixel count, ie. 640 x 480)

Quantization & Conversion (Rasterization)– Spatial Aspect describing grid location– Tonal Aspect describing color (Trichromacy considerations)

Output Frequencies– Pixel Grid– Spot Addressability Grid– Screener Dot Grid


Basic Image Processing Improve Correct Restore Analyze Change Archive Retrieve Synthesize Preparation (color, composition, & effects) Presentation or Viewing


Image Analysis Fundamental Processes

– Counting– Measuring– Matching– Classifying

Segmentation Feature Extraction Outlining (Skeletonization) Object Classification


CSI: Crime Scene Investigation Video Monitor Recording Analysis

– Restoration– Enhancement– Isolation & Extraction

Finger Print Matching Facial or Body Matching Feature Recognition Location Triangulation Spatial Placement & Measurement Document Analysis Ballistics & Trajectory Analysis


Image Analysis with ImageJBasic Operations

– Selection Tools: Select an image area (4 types of marques)

– Line Tools: Draw a line on an image (3 types of lines)

– Crosshairs: Mark image locations with coordinates & brightness

– Wand Tool: Automatically find the edge of an object

– Text Tool: Add text or labels to an image

– Magnifying Glass: Increase & decrease image size

– Scrolling Tool: Move image if larger than window

– Color Picker: Set the drawing colors


ImageJ Processing Undo Revert Cropping Clear Outside (make a perimeter to clear extraneous objects

around a subject area) Enhance Brightness/Contrast Remove Noise Rotate Image Convert to Grayscale (8 bit 256 shades) Thresholding (binary contrast enhancement) Counting & Measuring

– Setting the measurement scale– Measuring distance between points– Measuring Area– Counting particles


Seeing It In Print Traditional Printing is Binary

– Lay down ink– Don’t lay down ink

Halftone Solution– Dots smaller than eye resolution (150 lpi)– Illusion of continuous tone

Gray Levels 256 (16x16 spot grid)– (addressability (spi)/screen ruling (lpi))2 + 1– Needed gray levels - 16 + 4% noise for vignette

Halftone Methods - assigning halftone dots– AM Screening - Spatial address is constant, dot

size is modulated– FM Screening - Dot size is constant, spatial

addressing is modulated the higher the micron size, the coarser (more granular)

the print


Screen Ruling Commercial printing (GRACol)

– General Requirements for Applications inCommercial Offset Lithography

– 175 lpi Standard publication printing (SWOP)

– Specification for Web Offset Publishing– 133 lpi or 150 lpi (SWOPv2)

Newspaper printing (SNAP)– Specifications for Non-Heatset Advertising Printing– 85 to 100 lpi


Printing Color Print is reflective (subtractive) - CMYK separations represent color channels Each separation has its own screen AM screens are spatially offset (w/in90°)

– Yellow = 0° screen angle with Black = 45° angle– Cyan = 15° screen angle with Magenta = 75° angle

FM is random and eliminates angular screening– Many AM problems are overcome:

Loss of detail minimized Subject and screening moiré is eliminated Rosette structures are eliminated Gradient blends tend to print smoother


Image Storage Storage Systems

– DAMS & CMS– Desktop Systems

Adobe Bridge NikonView

Storage Media– CD (r & rw)– DVD– Magnetic (disk or other media)

Search & Retrieval Logic– Boolean Logic– Fuzzy logic


Search & Retrieval Mechanisms Key Words Search Fields Particular

Characteristics Color Recognition Matching Shapes Numeric Values Query By Image

Context (QBIC)

MeasurementParameters

Latitude & Longitude Slide Coordinates Time & Date Size or Density Thumbnails “Wild Cards” Cross Correlation


Image Compression Compression Reasons

– Transport– Storage

Standard Compression Schemes– Lossless: preserves exact image data content (ratios up to 3:1)– Lossy: preserves arbitrary levels of image quality (ratios up to 100:1)

Operational Symetry– Compression

Symmetrical: compression & decompression take similar time Asymmetrical: compression takes more time then decompression

– Decompression Asymmetrical: decompression takes more time than compression

Information Loss– Compression

Detail is lost in high frequency low contrast areas where the eye is notsensitive

– Down Sampling Information is lost throughout overall image resolution independent of

contrast


Compression Types Lossless (Transmissions & Facsimile)

– CCITT Group 3 & 4 - International Telephone &Telegraph Consultative Committee

– JBIG - Joint Bi-level Image Experts Group Lossy

– JPEG - Joint Photographic Experts Group Fine (1:4) Normal (1:8) Basic (1:16)

– MPEG - Moving Picture Experts Group MPEG-1: low resolution image sequences (320x240 pixels) MPEG-2: higher resolution applications (640x480 pixels)


Photo Compression & StorageRelative JPEG storage on 16 MB media

2560 x 1704

640 x 480

1024 x 768

1280 x 960

1600 x 1200

2560 x 1920

Pixel Size

271473:2

22914486VGA

1216937XGA

864724SXGA

593116UXGA

25126Full

Basic (1:16)Normal (1:8)Fine (1:4)Image Size

Courtesy of Nikon: The Nikon Guide to Digital Photography with the CoolPix 5700 Digital Camera


III. Image Evaluation

Image condition is bothperceptual and quantitative


Image Quality Image Resolution:

– Spatial Density & Frequency (high & low)– Brightness, Contrast, Color– Optics - system capability to resolve details

Dependencies:– Number of Pixels (pixels/inch)– Number of Lines (lines/inch)– Range of Brightness Values (dynamic range - gray levels)

Radiant intensity - reflected light Luminous brightness - acquired light

– Color & Contrast– Viewing Geometry

Image dimensions Viewing distance Aspect ratio (rectangularity)

– Compression Ratios & Relative Results


Quality Deficiencies Detail Resolution Image contrast & white balance Color Quality Tonal Quality & Range Composition Spatial Characteristics Annoying Image Noise Out-of-focus (specific objects or overall) Motion blur (specific objects or overall) Image Geometry Lost Information from Compression


Causes of Image Defects Limitations of Optics

– Built-in Limitations– Dirt, Particles, Smudges

Imperfect Detectors Inadequate Illumination Non-uniform Illumination Too Much Illumination An Undesirable Viewpoint (perspective) Unplanned Movement

– The Subject– The Capture Device– Capture Device Settings (Aperture & Shutter Speed)


Noise Definition - random extraneous pixels that are

not part of the image detail Causes

– High ISO setting– Under exposure– Shooting in darkness with long shutter speed

Types– Luminance Noise: gray scale data, grainy, patchy– Color Noise: colored artifacts– Compression artifacts– Film grain patterns from scanning– Scanner or camera sensor generated noise


Image Distortion Barrel Distortion - lens defect causing

lines to bow out Pincushion Distortion - lens defect

causing line to bow in Vignetting - image edges and corners

darker than center Chromatic Aberration - color fringes

along edges of image objects


IV. Image Correction

Making the image “better”


Correction Strategies Better to optimize or correct the

acquisition process– Not always practical, feasible, achievable– Not always possible

Correct after image is digitized & stored– Corrections may not deliver the highest

quality result– Corrections depend on planned purpose

(desirability vs. usability)


Approaches Processing Viewpoint:

– Subjective - repetition until satisfactory– Objective - measured and applied once

Processing Types:– Contrast enhancement or degradation– Spatial enhancement or degradation


The Correction Setup Lighting (approximately 65K) Digital Camera (settings if appropriate) Calibration (monitor, scanner, printer) Standard profiles (hardware & software) Image profiles and metadata Image analysis & correction plan Conversion - convert images to TIFF


Correction Steps (per Adobe) Duplicate the original image or scan Check image quality & confirm resolution is

appropriate for use Crop image to final size & orientation Repair flaws in scan of damaged photos Adjust overall contrast or tonal range Adjust white balance to modify original photo

conditions Remove any color casts Adjust color & tone is specific parts to bring out

highlights, midtones, shadows, and desaturatedcolors

Sharpen the over-all focus of the image


Correction Techniques Contrast Expansion & Manipulation Neighborhood Averaging Gaussian Smoothing (to reduce noise) Median Filter Application (reduce shot noise) Conditional Smoothing Manipulation of Pixel Patterns in an area by

addition, subtraction, or averaging Segmentation (critical in creating information)

– Dividing an image into regions corresponding to structural units inthe scene

– Distinguishing objects of interest Halftone Removal Removal of Motion Blur based on vector of direction and

exposure time


Enhancement & Restoration Histogram Equalization & Filters Image Morphology

– Contrast Enhancement– Edge Enhancement & Skeletonization– Image Erosion - shrinking or removing selected objects– Image Dilation - expansion of selected objects

Geometric Transformation– Rotation– Scaling– Warping

Interpolation Segmentation (removing distracting or useless

information - ie. Background subtraction)


Specific Processes Complement Image - negative Histogram Sliding - brighten or darken image Binary Contrast Enhancement - create high contrast Brightness Slicing - create high contrast of an object Image Subtraction - remove common background info Image Division - spectral ratioing Image Addition - average identical scenes to reduce noise Low-pass Filter - attenuate image noise from high freq. Unsharp Masking - sharpen by subtracting a brightness-scaled image

from the original High-pass Filter - highlights high frequency details Sobel Edge Enhancement - produce object edges Shift & Difference Edge Enhancement - vertical, horizontal, and

diagonal edges


Specific Processes (continued) Prewitt Gradient Edge Enhancement - produce object edges in an

image Laplacian Edge Enhancement - extracts all edges in an image Line Segment Enhancement - produce edge-enhanced images Median & Ranking Filters - remove impulse noise spikes Fourier Frequency Transform Filtering - selective removal of periodic

noise patterns Translation Transformation - horizontal or vertical geometric

adjustments Rotation Transformation - geometric rotation of an image Scaling Transformation - geometric adjustment of size Warping Transformation - correct geometric distortions created in

image acquisition


V. Tools

Functionality for image manipulation


Key Photoshop Tools Dodge Tool - lighten highlights, reduce light Sponge Tool - saturate a color by adjusting purity Clone Stamp Tool - uses pixels in one area to

replace pixels in another area Spot Healing Brush - paints with sampled pixels from

around retouch area Healing Brush Tool - apply & blend pixels from one

area to another Patch Tool - combines area capture with blending

properties


Key Photoshop Filters Unsharpen Mask Filter - adjust edge contrast

giving illusion of better focus Reduce Noise Filter - eliminate noise Sharpen Filter - reduce lens blur Vanishing Point Filter - correct perspective Lens Correction Filter - address distortion

issues


References Adobe. (2005). Adobe Photoshop CS2 classroom in a book. Berkeley,

CA: Peachpit Press. Baxes, Gregory A. (1994). Digital image processing principles and

applications. New York: John Wiley & Sons, Inc. Haynes, Barry & Crumpler, Wendy. (2002). Photoshop 7 artistry.

Indianapolis, IN: New Riders Publishing. London, Sherry & Grossman, Rhoda. (2002). Photoshop 7 magic.

Indianapolis, IN: New Riders Publishing. McClelland, Deke. (2005). Adobe Photoshop CS2 one-on-one.

Sebastopol, CA: O’Reilly Media, Inc. Rasband, W.S. (2006). ImageJ. Bethesda, MD: U.S. National Institute

of Health. Retrieved October 25, 2006, from http://rsb.info.nih.gov/ij Russ, John C. (2002). The image processing handbook, fourth edition.

Boca Raton, FL: CRC Press LLC. Sigg, Franz. (2005). Resolution and contrast for image reproduction.

Slide Presentation. Rochester, NY: RIT.


Image Gallery

SettingsProcedures

Image Collection


Image Gallery - Settings Photoshop Color Settings

– RGB: Adobe RGB (1998)– CMYK: U.S. Web Coated (SWOP) v2– Gray & Spot Colors: 20% Dot Gain– Embedded Profiles: Preserve– Rendering Intent: Relative Colorimetric– Color Engine: Adobe (ACE)– Black Point Compensation & Dither

File Save– TIFF with LZW (Lossless) Compression– Interleaved– Macintosh

Acrobat– Default settings for High Quality Desktop Printing


Image Gallery - Procedure Load Image into Photoshop Convert Profile (sRGB to Adobe RGB) Apply Process(es) or Filter(s) Resize Image Save As… in Processed Image Folder


Original Photograph

Photograph with Flash

Manually CorrectedPhotograph usingColor Balance for Shadows, Mid-tones,and Highlights

Manually CorrectedPhotograph usingContrast & Brightness

Auto CorrectedPhotograph across Levels

Auto CorrectedPhotograph for Color

Auto CorrectedPhotograph for Contrast

Yellow Flower Collection


Photograph manually adjusted forbrightness and contrast by holdingone setting at 0 while adjustingthe other setting

Original Photograph

Brightness = -49Contrast = 0

Brightness = -100Contrast = 0

Brightness = 49Contrast = 0




Brightness = 0Contrast = -49

Brightness = 100and Contrast = 100

produces Neutral Gray

Brightness = 0and Contrast = -100

produces Black

Brightness & Contrast


Photograph manually adjusted for Shadows,Mid-tones, and Highlights to increase the

Greens and strengthen the yellows

OriginalPhotograph

Photograph afterSlight Adjustments

Color Balance


Application of Image-Wide Adjustments toTone and ColorOriginal Photograph

Tone & ColorEqualized

Tone & ColorPosterized

Tone & ColorInverted

Tone & ColorThresholded

Purple Flower Collection


The original photograph was takenout of focus

This correction is by applying SmartSharpening: Correction Angle 90°

Radius 40 PixelsMotion Blur Correction

This correction was made by applyingthe Unsharp Mask: Amount 90%

Radius 16.6 PixelsThreshold 48 Levels

Patio Stones - Sharpening


The object is to bring more detail toTyler (the dog).

#1. The original photograph#2. The desaturated photograph#3. Adjusted highlights and shadows:

Shadows set to 100%Highlights set to 0%#1

#2 #3

Bringing Out Detailswith Shadows & Highlights


Tyler is not visible in the originalphotograph (upper left), but hebecomes obvious in the two gradient-mapped versions below (see thecircled areas).

I had no idea he was in the pictureuntil it was mapped. It was acomplete surprise.

Bringing Out Details withGradient Mapping


While Tyler is not visible in theoriginal photograph (previous slide),and somewhat visible with GradientMapping, he is easily located in thesetwo filtered images.

The upper image was created withthe Find Edges Filter.

The lower image was created with theContour Filter where the Levels wereset to 8 to eliminate detail

Bringing Out Detailswith Contour and

Edge Filters


Bee Collection - UsingMasks, Marques, andTransformation Edits


The original photograph with someposterization tendency in the upperleft darker blue sky

A Cool 80 filter applied to photographstill leaves a small amount ofposterization tendency in the upperleft darker blue sky

A Warm 85 filter mitigates theposterization tendency and softensthe colors overall

Adjustments with PhotoCool and Warm Filters


The original photograph with somedetail lost in the shadows and somesharpness overall

A blue filter applied to photograph stillsoftens the photo but is a little cool

A yellow filter warms the photograph,bringing out some green and a littlemore detail

Application of filters (in this case)demonstrates viewer perception andsubjectivity

Adjustments with PhotoColored Filters


Original Photograph Cyan Proof Plate Magenta Proof Plate Yellow Proof Plate

Black Proof Plate CMY Proof CMYK Proof

Plate ProofSeparations


The original photograph wascompressed during File Save As…

1. Original TIFF Image2. JPEG - Maximum3. JPEG - High4. JPEG - Medium5. JPEG - Low

1.

2.

3. 4. 5.

JPEG Compression


ImageJ RGBSeparation

Separated Red Separated Green Separated Blue

Merged RGB

The original photograph wasseparated using the ImageJ image

separation procedure.

This produced three images that wereremerged using a reciprocal procedure

to generate the fourth image.

Original Photograph


ImageJ ChristmasCollection - Analysis

Original Color Photograph

Converted 8 bit Gray Scale Image

Histogram

BaselinePlot


ImageJ Christmas Collection- Procedures & Filters

Three procedures were run to identify detail:

1. Identify areas of high variance2. Find edges3. Apply a convolution filter

1.

2. 3.


ImageJ Collection - ApplySubtraction & Filters

Additional processes brought out more detail:

1. Subtract the background leaving white areas2. Adjust shadows for south west shift3. Apply a sharpening filter

1.

2. 3.


ImageJ Christmas Collection- Contrast & Gamma

Two Additional processes were applied:

1. Enhance Contrast2. Adjust Gamma to 1.0

2.

1.


End of Galleryand

Presentation

Thank You for Your Attention

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Digital Imaging Study