dallas genealogical society technology special interest groupdemystifying digital images tony hanson...

Dallas Genealogical Society Technology Special Interest Group

Thursday, April 2, 2015

Tony Hanson Webmaster

Technology Special Interest Group Leader Director - Education

Demystifying Digital Images

Tony Hanson Webmaster

Technology Special Interest Group Leader

What we will be talking about • What is a Digital Image • How Digital Images are Created • Numeric Representation of Colors • Histograms • How Digital Cameras and Scanners Work • Digital File Formats • Image Resolution and Size • Printing Images • Metadata • Resizing Images

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What is a Digital Image?

• A numeric representation of an image • Comprised of an organized collection of Pixels

(Picture Elements) – Rows & Columns – Pixel a.k.a. ‘Dot’

• When viewed on a suitable display (or printed) it appears to be an exact copy of the original image

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02/2015 5 “Prairie Passage” by Carl and Sandra Bryant

Eagleville, MO Welcome Center

Mosaic Image

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Notre Dame Cathedral, Montreal Canada

How Are Digital Images Created?

• ‘Born Digital’ – Created using software that directly creates the

digital file – File -> Save As ->

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This is an image file created directly from Publisher

Graphic Images

• Has relatively Few colors • Usually a (relatively) small file • Some file formats are customized to support

this type of image

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How Are Digital Images Created?

• Converted to a digital format – Scanner – Digital Camera – These both use a Charge Coupled Device (CCD) to

convert the optical image into an appropriate numeric representation

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CCD: Converts Light to a Numeric Value

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Memory CCD

Color values are represented by three components: • Red • Green • Blue

Light

x

y z

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Color Palette

Red

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Memory CCD

255

0

0

Green

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Memory CCD

0

255

0

Blue

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Memory CCD

0

0

255

White

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Memory CCD

255

255

255

Black

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Memory CCD

0

0

0

Purple

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Memory CCD

136

109

249

Gray

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Memory CCD

179

179

179

Note that the color values are all the same for Gray….

Numeric Representation

• Color • Gray Scale • Black and White

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Numeric Representation: Color

24 Bit Color Depth • Each component value (Red, Blue and Green)

can range from 0 to 255 – In Binary, the range is

• 0: 00000000 • 255: 11111111

• 3 Colors x 8 bits each = 24 bits

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255 in Binary Notation

1 2 6 3 1 8 4 2 6 8 4 2 1 1 1 1 1 1 1 1 1 128+64+32+16+8+4+2+1 = 255

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48 Bit Color

48 Bit Color Depth • Each component value (Red, Blue and Green)

can range from 0 to 65,535 – In Binary, the range is

• 0: 00000000 00000000 • 65536: 11111111 11111111

• 3 Colors x 16 bits each = 48 bits • Provides more colors

– More steps between Black and White 02/2015 25

65,536 in Binary Notation 3 1 2 6 8 4 2 1 7 3 1 0 0 0 5 2 1 6 8 9 9 4 2 1 5 2 6 3 1 8 4 2 6 8 4 2 6 8 4 2 6 8 4 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 32268+16324+8192+4096+2048+1024+512+256 = 65280 128+64+32+16+8+4+2+1 = 255 65280+255 = 65535

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Black is Still Black

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Memory CCD

00

00

00

White is still White

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Memory CCD

65535

65535

65535

More shades of Blue (and Red, Green…)

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Memory CCD

0

0

65535

Gray Scale

• Ranges from White through various shades of Gray to Black – Has equal Red, Green and Blue values – Since each of the three values is the same it is

only necessary to record it once

• This limits the colors available, but may produce a high quality image that requires less storage

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Grayscale Palette

Gray Scale Color Depth

• Usually available in 8 bit and 16 bit color depth

• The end points in both cases are still White and Black

• 16 bits gives you more granularity – More shades of Gray

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Black and White ( a.k.a. ‘Line Art’)

• Each Pixel can have one of two values: – 0 => White – 1 => Black

• It is usually possible for you to modify the threshold between what is considered Black and what is considered White

• These values (0 or 1) can be stored in a single bit, significantly reducing storage requirements

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Size Matters!

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Source: ‘A few scanning tips’ http://www.scantips.com/basics1d.html

How many Pixels at each color?

How Many Pixels

0, 0, 255 0, 255, 0 255, 0, 0 0, 0, 0 255, 255, 255

“Black” “White”

27

53

26

“Blue” “Green” “Red”

A Histogram!

0, 0, 255 0, 255, 0 255, 0, 0 0, 0, 0 255, 255, 255

“Black” “White”

How Many Pixels

Count of How Many Pixels at each color

s

Histogram

• Shows a count of each ‘color’ in the image • Helps understand how much contrast the

image has – Probably most useful to photographers (useful for

judging exposure) – Also useful when adjusting scanner threshold

settings

s

Digitation Tools

• Camera • Scanner

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Digital Camera

Image Lens Charge Coupled Device

Light

Shutter

Aperture

s

Image on a Charge Coupled Device (CCD)

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Pixels

CCD Characteristics

• How sensitive it is to Light • Its Size • How many Megapixels • Aspect Ratio

– Ratio of Width to Height (Pixels) – A square would have an aspect ratio of 1 – Typical values for a camera are 1.3 or 1.5

(rectangular)

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• Records images in a 3264 by 2448 format – 3264 x 2448 = 7,990,272 Pixels (8 MegaPixels) – 3264 / 2448 = 1.33 to 1 Aspect Ratio

2448

3264

iPhone 6

Scanners

• Unlike a camera, a scanner has only a single row of CCD sensors

• The sensor is moved across the document to be scanned and takes many samples in the process

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Flatbed Scanner

Document Light

Charge Coupled Device

Mirrors

Glass

Document

My Simple Document

Tony.

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Each Line scanned as a series of Pixels…

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Scanner Specifications

• Optical Resolution – The Pixels per Inch capability of the CCD (Horizontal resolution)

• Hardware Resolution – The resolution of the mechanism that moves the CCD across the document (Vertical Resolution)

• Interpolated Resolution – Using software to increase resolution by predicting what might be in between two scanned pixels

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How are digital images saved?

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Digital File Formats

• A digital file format defines the way that the digital information will written into (and read from) the file

• Many file formats have been created over the years to address different needs and concerns – Wikipedia has identified 262 different graphics file

formats!

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https://en.wikipedia.org/wiki/Comparison_of_graphics_file_formats

Image File Format Characteristics • Raster vs. Vector • Compression Type • Color Depth • Color Indexing • Transparency • Metadata • Interlacing • Animation • Layers • Color Management

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Raster vs. Vector

Vector formats deal with lines and shapes • These scale (adjust to different sizes and

display formats) very well • Useful in graphic and scientific applications Raster formations deal with pixels/dots • The focus of our discussion

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Compression

• Not all formats perform compression • Those that do fall into two classes:

– Lossless • No loss of resolution or color information • Results in larger files

– Lossy • Some irreversible loss of resolution or color information

in the compression process • Results in smaller files

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Color Depth

• Defines the number of bits available to encode color – Usually can be modified – Ranges from 1 to 48 bits

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Color Indexing

• Some formats limit the number of discrete colors that can be utilized

• They provide a fixed size matrix where the colors utilized in the image can be specified

• During the encryption, each pixel’s color is referenced to this table – Advantage: Smaller File – Disadvantage: Limits the color granularity of the

image

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Transparency

• Not supported by all formats • Allows the background to be viewed behind

the image • Achieved by designating a specific color in the

image • When displayed, image pixels with the

designated color are discarded and replaced the appropriate pixel from the background image

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Metadata

• Not supported by all formats • Descriptive information about the image • Appended to the image file • There are a variety of metadata types/standards

that can be used • The most common are:

– Exif – Photographic Information – IPTC – Descriptive Information – XMP – ISO Standard

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Popular Image File Formats

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TIFF

• Compression: None • Color Depth: 1,2,4,8,16,24,32 bit • Color Indexing: Yes • Transparency: Yes • Metadata: Yes • Comments

– Can be compressed with external/3rd party compression tools

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JPEG

• Compression: Lossy • Color Depth: 12/24 bit • Color Indexing: No • Transparency: No • Metadata: Yes • Comments

– Amount of compression can be varied – Repeated saving compounds color loss

• a.k.a. ‘JPEG Artifacts’ – Good for photos, bad for text or graphics

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JPEG vs TIFF

• Original TIFF File – 5036 x 8326 Pixels – 600 dpi – 25,667 KB

• Large JPEG – 5036 x 8326 Pixels – 600 dpi – 15,360 KB

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• Medium JPEG – 5036 x 8326 Pixels – 600 dpi – 3,146 KB

• Small JPEG – 5036 x 8326 Pixels – 600 dpi – 1,567 KB

JPEG Artifacts

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Loss of: • True Color • Correct Intensity • Resolution

GIF

• Compression: LZW • Color Depth: 1,2,3,4,5,6,7,8 bit • Color Indexing: Yes • Transparency: Yes • Metadata: Yes • Comments

– LZW compression had licensing/legal issues that limited its widespread use

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PNG

• Compression: Lossless • Color Depth: 1,2,4,8,16,24,32 bit • Color Indexing: Yes • Transparency: Yes • Metadata: Yes • Comments

– Much better choice than JPEG – Some consider it to be nearly as good as TIFF – W3 endorsed replacement for GIF

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JPEG 2000

• Compression: Lossy or Lossless • Color Depth: Color up to 48 bit • Color Indexing: No • Transparency: Yes • Metadata: Yes • Comments

– Popular with governments and institutions – Not yet widely supported in the consumer market – Eventual replacement for TIFF

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Metadata

• Data about something • Digital Metadata is Embedded in each file

Pre-Digital Metadata • Date (Aug 61) • Description

(Hanson – Evans – Tollief’s Fam)

File Format

Image Data

(Pixels)

Camera Data (EXIF)

MetaData

Exchangeable Image File Format

Format Specific (TIFF, JPG, PNG, etc…)

IPTC: International Press Telecommunications Council

• The most widely recognized standard for Metadata

• Established in 1965 by a group of news organizations

IPTC Defined For Many Image File Types

• You can define IPTC metadata for the following image formats: – .tif – .jpg – .png

• … But NOT for these image formats: – .bmp – .gif

Viewing or Printing an Image

• Requires software that understands the file format

• Extracts the data and re-creates the image • Computer monitors and printers present

images in very different ways – This may impact how the image appears to you

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How Big Is That Image?

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• Digital images have no ‘size’ • However, they do have characteristics that

may limit how large you want it to be when it is displayed or printed

This is a stamp

• The original is 1 ¼ inched tall and 1 inch wide • Scanned at 300 dpi

– 300 x 375 dpi

s

1920 x 1080 Resolution

A 1 ¼ inch tall stamp scanned at 300 dots per inch

1280 x 720 Resolution

A 1 ¼ inch tall stamp scanned at 300 dots per inch

800 x 600 Resolution

A 1 ¼ inch tall stamp scanned at 300 dots per inch

Pixels and Colors

• Computer Monitors will always display images with truer colors when compared to most home printers

• This is because each pixel on a monitor can display the entire possible range of colors – A printer can only approximate the color using a

mixture of colors

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Printing Images

• Printers used at home (generally) can only print dots – Black and White printers can only create black

dots (or no dots at all – a.k.a. ‘white’) – Two modes of printing:

• Line Art • Shades of Gray

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Line Art

• Dot for dot representation of the image • Good for text & some (limited) types of

images

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Shades of Gray

02/2015 79 HP 1320 Laser Printer: Prints at 1200 dpi

Shades of Gray

02/2015 80 Scanned at 9600 dpi

Grid Sizes

• 6 x 6 – 37 Shades of Gray, reduces resolution by a factor of 6 – 600 dpi -> 100 Line Per Inch (lpi) – 1200 dpi -> 200 lpi

• 7 x 7 – 50 Shades of Gray, reduces resolution by a factor of 7

• 8 x 8 – 65 Shades of Gray, reduces resolution by a factor of 8

• 10 x 10 – 101 Shades of Gray, reduces resolution by a factor of 10

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Printing Color Images

• Printers used at home (generally) can only print dots – Color printers can only print the colors for which

they have ink • Cyan, Magenta, Yellow and Black • Cyan, Magenta, Yellow , Black, light Cyan, Light

Magenta

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Printing Colors

• Colors are created by placing different colors close together – One color image (pixel) requires many printer ink dots – The human eye cannot distinguish the individual

colors and will perceive the mixed color – Called Dithering

• This is why (for example) we need a 1200 dpi printer (ink dots) to print an image at 250 dpi (pixels).

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Printer dpi Specifications

• Printer specifications are real, accurate and meaningful, but are not to be confused with image resolution

• Printer ink dots and image pixels are very different things

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Rule of Thumb

• The effective resolution (image pixels per inch) should be in the range of 150 – 300 dpi (for the actual printed dimensions)

• Sending images at higher resolutions is counter productive – Files are larger – Most of the pixels will be thrown away – May actually decrease the quality of the printed

image

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1 ¼ x 1 inch Original

• Scanned at 300 dpi • OK to print it at its original size

– Effective resolution would be 300 dpi

• Could print it twice as large (2 ½ x 2 inches) – Effective resolution would be 150 dpi

• Larger images would probably not look good – If desired, scan again at higher dpi setting

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Image Resizing

• Scaling • Cropping • Resizing

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Image Resizing: Scaling

• Scaling – Specifying a dpi value to use when printing – Just a numeric value that is saved with the image

and used if/when it is printed – The original image remains unchanged – Defined for TIF and JPG

• Not all applications pay attention to this value

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Scaling

• Stretching or shrinking the image to fit a specified area

• Can be done while scanning or afterwards..

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Scaling: Photoshop 12 Image -> Resize -> Image Size…

Image Resizing: Cropping

• Selected part of the original image • The original image remains unchanged

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Image Resizing: Resizing

• Resizing – Alters the dpi of the image – The original image IS CHANGED

• Best to work on a copy!

– Works better when you DECREASE the dpi value • You can increase, but you are asking the software to

make an educated guess about the pixels it adds

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Resizing: Photoshop 12 Image -> Resize -> Image Size…

Other Modifications

• Orientation (Portrait / Landscape) • Contrast

– Modifying what is considered ‘white’ and what is ‘black’

• Color Balance • File format conversions • Much more…

– Ask Sandra Crowley to give her Image Editing seminar again….

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More on Size and Resolution

• Let’s assume we want to digitize a document that is 8.5 x 11 inches (the entire document) – Using an 8 Megapixel Digital Camera – Using a Flatbed Scanner

• Questions: – What is the best resolution I can obtain using the

camera? – What dpi setting would I need to use on the

scanner to obtain better resolution?

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Best Case

• We want to maximize the resolution of the image by using as many pixels as possible – Use all of the horizontal pixels (2448) – Determine how many vertical pixels we can use…

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3264

2448

Math!

2448 / 8.5 = x / 11 x = ( 11 * 2448) / 8.5 x = 3168 Unused Pixels: (3264 – 3168) * 2048 = 96 * 2048 = 196,608 (2.5%)

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3264

2448 Pixels 8.5 Inches

96

3168 Pixels 11 inches

What is our effective resolution?

• 2448 Pixels / 8.5 inches = 288 Pixels/inch • 3168 Pixels / 11 inches = 288 Pixels/inch

To obtain a higher resolution image using a scanner we could scan it at 300 dpi.

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Another Example

• I have a slide (1 inch High x 1.5 inches Wide) • I want to print a 4 x 6 image • What dpi setting do I need to use on the

scanner to scan the slide?

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Solution

• I want to sent a 4 x 6 image at a density of 300 dpi to the printer.

• A 4 x 6 image is exactly 4 times the size of the slide (they have the same Aspect Ratio) – 1 x 4 = 4 – 1.5 x 4 = 6

• Since I am enlarging the image by a power of 4, I will also be decreasing the resolution by a power of 4 – 300 dpi (printed) = dpi (scanned) / 4 – dpi(scanned) = 4 * 300 = 1200 dpi

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1.5 inches 1800 Pixels

1 inch 1200 Pixels

4 inches 1200 Pixels (300 dpi)

6 inches 1800 Pixels (300 dpi)

What if I wanted an 8 x 10?

• (6 * 1 x 1.5) = 6 x 10 – Not big enough!

• (8 * 1 x 1.5) = 8 x 12 – Too big! – Need to crop 2 inches off the width – Could take 1 inch off each side – Let’s assume that this will work for the image…

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Solution

• We still want an effective density of 300 dpi • Enlarging it by a factor of 8 • 8 * 300 = 2400 dpi • Scan the slide at 2400 dpi, crop to 8 x 10 and

print! – Check:

• ( 1 * 2400 ) / 8 = 300 dpi • ( 1.5 * 2400) / 12 = 3600 / 12 = 300 dpi

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References/Resources

A few scanning tips Wayne Fulton

http://www.scantips.com/

• Invaluable reference! • Also good tips on photography…

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Scanning 101 – The Basics * START - The First Fundamental Concept Video Resolution - How much to scan?

Say No to 72 dpi - It's a false notion Images for television or for PowerPoint

Printing Resolution - Scaling and Resampling Finding the Scaling and Resampling Menus

Printer Resolution - How much to scan? Line art and Threshold - Copy and OCR, Printed Text

Line art and Grayscale Scanning for Fax Descreen to remove Moiré Interference Images in magazines/books/newspapers Interpolated Resolution - 9600 dpi? Photo Resolution - How much can we scan? Image File Formats - Which format? Video Boards Transparent Media Adapter - 35 mm slides? What about Film Scanners? Dynamic Range - 24 bit or 36 bits?

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Wikipedia

Comparison of graphics file formats

https://en.wikipedia.org/wiki/Comparison_of_graphics_file_formats

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Epson Technical Brief

• Discusses Image Quality, Performance and Flexibility of Epson Scanners

• A good overview of technical aspects of scanner design and operation https://files.support.epson.com/pdf/exp16_/exp16_ts.pdf

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Questions?

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Thank You!

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Tony Hanson Webmaster

Technology Special Interest Group Leader

http://www.dallasgenealogy.org