Digital Imaging Basics

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Digital Imaging Basics

• Staff Development Continuing Education Series

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What well discuss

• Pixels
• Resolution and Resizing
• Color
• File formats
• Hardware Software

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Resolution and Resizing

• you say you want a re(s)olution

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Digital Images and Pixels

• Digital Images are composed of digital elements
  called pixels.
• Pixels are bundles of digital information about
  the color of a specific spot in the image.
• They are organized into a grid to convey the
  image.

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Patterns of dots produce the effects of
consistent color The size of each pixel is
determined by print size.
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Digital Images and Pixels

• The RESOLUTION is the ratio of the number of
  PIXELS to the PRINT size.
• Resolution of pixels on the longest side
• print size
• Resolution is
• used to judge the quality of the image.
• Most often measured in pixels (or dots) per inch
  or ppi.

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The Big Picture

Increasing size without increasing resolution
stretches out the dots of color.
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The Big Picture

.5 x.75 _at_ 72dpi6.5 kb
4 x 5 _at_ 10 dpi6.5 kb
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The Big Picture

Resolution SHOULD decrease when you enlarge, but
if you scan at a high resolution, the loss
wont be as severe.
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The Big Picture

.5 x.75 _at_ 575dpi113 kb
4 x 5 _at_ 72 dpi113 kb
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Changing the document size alone doesnt change
the pixel dimensions or the file size
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Before 6.569 x 6.694 inches (473x482
pixels)72dpi667.9K
After3 x 3.057 inches (473x482 pixels)158
dpi667.9K
The number of pixels doesnt changejust the
print size of them.
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Print-size and resolution are inversely related
Print-Size
Resolution
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Resampling can change the number of pixels,
which can therefore change the file size
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Before 6.569 x 6.694 inches (473x482
pixels)72dpi667.9K
After3 x 3.057 inches (473x482 pixels)72
dpi139.3K
After6.569 x 6.694 inches (105x107 pixels)35
dpi32.9K
Resampling can be done to any of the variables
(print size, number of pixels, or resolution)
independently of each other. Resampling breaks
the relationship between the variables. It always
results in file size change because I add or take
away pixels.
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Resampling breaks the relationship between
resolution and print size
Print-Size
Resolution
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?
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?
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A Warning
?
It is possible to resample up or interpolate.
The computer adds in new dots and guesses their
color. The quality is typically poor
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.5 x.75 _at_ 72dpi6.5 kb
4 x 5 _at_ 72dpi323 kb
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Why Resample?
Resampling is used to change image quality for
specific purposes
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Print Quality
Good consumer printers can print up to about 275
ppi. Commercial printers are often much
better. 300 dpi is a print industry standard.
The human eye usually cant appreciate detail
higher than 300 dpi from about 8 inches distance
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Monitor Quality
Regardless of the print size you dictate, the
monitor will always display 72 pixels in each
inch (unless your browser program creates a
temporary view). If you scan something at 300
ppi and show it on a monitor, it will be resized
to 72 ppi meaning a 5 inch image would be 21
inches. These images look as good as print
images to your eye because of optical illusion

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Color palettes

• 16(-bit) and what do you get?

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Painting with Pixels

• What are pixels made of?
• Pixels are a string of code (a series of 0s or
  1s) that signify directions for different colors.
  
• Each 0 or 1 is called a bit.
• The number of bits in the pixel determines the
  color palette.
• More bits more combinations more possible
  colors
• This is called bit-depth

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Painting with Pixels

• How does bit-depth affect color?
• 1-bit two colors (0 or 1 for each pixel)
• 2-bit four colors (00, 11, 01, 10)
• 4-bit 16 colors (0000, 0001, 0100, 0101, 0111,
  etc.)
• 8-bit 256 colors (00000000, 001, 010.. 011...,
  001, 111)
• 16-bit 65,536 colors (00000, 000, 0, 0, 0,
  0, 0)
• The more colors you can use, the more realistic a
  picture looksand the bigger the file is

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Painting with Pixels

• Multi-channel Color (RGB)
• 3 channels (R,G,B) _at_ 8-bit 24 bits per pixel
• 256 kinds of Red
• 256 kinds of Green
• 256 kinds of Blue
• Combined to make millions of colors
• 3 channels (R,G,B) _at_ 16-bit 48-bits per pixel
  
• 65, 536 kinds of Red
• 65,536 kinds of Green
• 65,536 kinds of Blue
• Combined to make BILLIONS of colors

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1-bit, black and white
8-bit grayscale
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1-bit, black and white
8-bit grayscale
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1-bit, black and white
8-bit grayscale
24-bit color
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Which looks better to you?
8-bit grayscale
24-bit color
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24-bit color
8-bit color
Can you tell the difference here?
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8-bit or 24-bit? Can you tell the difference
here?
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24-bit or 48-bit? Can you tell the difference
here?
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Palatable Palettes

• The proper color palette to use depends on the
  image and how you will use it

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Palatable Palettes

• Which Color Settings to Use?
• 1-bit Black White
• text with no artifactual value mainly for
  large-scale book scanning, ILL scanning
• 8-bit, 1 channel Indexed color or grayscale
• web graphics and thumbnails, NOT continuous tone
  images
• text with some artifactual value sometimes with
  black and white images
• 8-bit, 3 channels (24-bit) RGB
• manuscript text, photographs, slides, etc.
• 16-bit, 1 channel (16-bit) Grayscale
• Best for grayscale images that will need major
  adjustment post-scan
• 16-bit, 3 channels (48-bit) RGB
• Best for continuous tone images that will need
  major adjustment post-scan

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Saving and sharing

• save the last (file) for me

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Saving and Sharing

• Raw formats straight from the camera or
  scanner no post-processing or organizing the
  data only usable in a very limited number of
  applications
• TIFF usually the largest digital files
  supports many color profiles different options
  for compression cannot be displayed in a browser
  or email
• JPEG2000 smaller than TIFFS supports multiple
  color profiles different options for
  compression doesnt work in many browsers or
  email
• JPEG much smaller than TIFFs viewable in web
  browsers variable amounts of compression
• GIF very small files using an index color
  schemebut uncompressed viewable in any
  browser.
• PDF great for sharing, especially text web
  compatible an open standard though not always a
  preservation one not ideal for saving/reusing
  images

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Saving and Sharing

• Compression
• Lossless
• Compresses data but keeps the directions to
  reconstruct it. Doesnt compress as much as lossy
  compression.
• Lossy
• Similar information is lumped together

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Uncompressed image 72 dpi 8 bit RGB color 83 KB
Compressed image 72 dpi 8 bit RGB color 30 KB
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Uncompressed image 72 dpi 8 bit RGB color 83 KB
Compressed image 72 dpi 8 bit RGB color 39 KB
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Saving and Sharing

• So, how do we save it?
• A copy to keep? (hi-res, original size, big file)
• Tiff? JPEG2000?
• A copy to print? (med- to hi-res, determined
  size, big to medium file)
• A 300 dpi JPEG? JPEG2000? A PDF?
• A copy to view? (lo-res, determined size, small
  file)
• A 72 dpi JPEG? JPEG2000? A PDF?
• A copy for comparison? (lo-res, small size, small
  file)
• A 100x100 pixel JPEG? A 100x100 pixel GIF?
  JPEG2000?

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Setting Up Shop

• (baby we were) Born to Scan

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Flatbed Scanners

• Pros
• Reasonably good resolution and color management
• Can be adapted to fit both reflective and
  transparent materials
• Stands up to repeated use
• Easy to use (usually)

• Cons
• Limited bed size
• Lower resolution and quality than specialty
  scanners (some)

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Slide or Film Scanners

• Pros
• High resolution
• Some models can handle both 35mm and medium slide
  formats
• Cons
• Can only handle slide or film of specific sizes
• More expensive than flatbeds

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Overhead Scanners

• Pros
• Can handle oversize materials, fragile books,
  other odd formats or fragile materials
• Usually come packages with software to do
  sophisticated image edits or batch processing
• Some have robotic page turning elements
• Cons
• Difficult and time consuming to operate
• Expensive
• Low resolution

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Drum and Roll Scanners

• Pros
• Can accommodate large formats
• Can capture in true CMYK colors
• Capable of very high resolutions
• Cons
• Materials must be sturdy yet flexible
• Can damage materials
• Only appropriate for reflectivematerials

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Scanning Software Differences
Different interfaces have similar basic features
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Scanning Software Differences
Epson Scan in Professional Mode
Color settings lists bit-depth but not RGB
Both resolution and print (document) size are
changeable
Epson Interface
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Scanning Software Differences
Epson TWAIN
Color settings lists document types but not RGB
Both resolution and print (document) size are
changeable
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Things to look for in a scanner

• High optical resolution
• Scanner specifications usually include an
  optical and interpolated resolution (and now
  we know interpolation is bad)
• D-max or dynamic range
• The lightest light and the darkest dark the
  scanner can see. You want at least 2.0 (scale
  from 1.0 to 4.8)
• At least 24-bit external color
• Another trickinternal or hardware is
  meaningless
• A transparency adapter
• If you want to scan slides too
• Take the manufacturers word with a grain of salt

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Digital Cameras

• Pros
• Good for 3-dimensional objects
• Good resolution and zoom
• Can capture materials from multiple angles
• Area-array (vs. line-array)
• Cons
• Quality can be dependent on skill of
  photographer and external factors like lighting
• Probably not as good for flat materials as a
  scanner

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More ways to say the same thing

• Megapixel
• Maximum number of pixels in an image
• Resolution will depend on what size you print the
  image
• When you open the image on your computer it will
  default to 72 ppi
• Optical Zoom vs. Digital Zoom
• optical zoom is actual zooming with the lens
• digital zooming is resampling! The quality
  suffers

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Photo Editing Software

• Adobe Photoshop
• Expensive (699 to 999) professional quality
  more tools than you will probably ever use the
  ability to adjust everything manually
• Adobe Photoshop Elements
• Much less expensive (80) intuitive adobe
  design auto tools instead of manual ones
• Corel Paint Shop Pro
• Much less expensive (50) similar tool set a
  little less intuitive than Photoshop auto and
  manual tools
• GIMP
• Free (0!) similar tool set, but often different
  terminology auto and manual tools

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Demonstration?

• Do we have time for a