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Digital Library Leadership
Montgomery, AL ● April 20, 2004
A Scanning Primer
A Scanning Primer
Presented by: Beth Nicol & Todd Jennings
Digital Library Leadership
Montgomery, AL ● April 20, 2004
OverviewOverview• Resolution• Color Space• File Types• OCR• Compression• De-Screening/Moiré Removal• Image Touchup
• Resolution• Color Space• File Types• OCR• Compression• De-Screening/Moiré Removal• Image Touchup
Digital Library Leadership
Montgomery, AL ● April 20, 2004
Resolution (DPI/PPI)Resolution (DPI/PPI)• DPI > “Dots Per Inch”• PPI > “Pixels Per Inch”
– Image resolution is measured in the number of pixels (equally sized squares) can be laid down over an image.
– “a picture element”– the smallest element that can be assigned
one and only one color or shade value
• DPI > “Dots Per Inch”• PPI > “Pixels Per Inch”
– Image resolution is measured in the number of pixels (equally sized squares) can be laid down over an image.
– “a picture element”– the smallest element that can be assigned
one and only one color or shade value
Digital Library Leadership
Montgomery, AL ● April 20, 2004
Resolution ExamplesResolution Examples
Digital Library Leadership
Montgomery, AL ● April 20, 2004
Bit Depth: TermsBit Depth: Terms• “BiTonal” > 1-bit
– A one-digit string > 1 or 0 > black or white
• “Grey Scale” > not more than 8-bit– an eight-digit string > 256 colors or shades
• “True Color” > not less than 24-bit– a twenty-four digit string > 16,777,216
colors
• “BiTonal” > 1-bit– A one-digit string > 1 or 0 > black or white
• “Grey Scale” > not more than 8-bit– an eight-digit string > 256 colors or shades
• “True Color” > not less than 24-bit– a twenty-four digit string > 16,777,216
colors
Digital Library Leadership
Montgomery, AL ● April 20, 2004
Color SpaceColor Space• sRGB
– “standardized” Red / Green / Blue– optimized for screen viewing
• CMYK– Cyan / Magenta / Yellow / Black– Optimized for printing
Most library and image digitization is archived in the sRGB color space, i.e. for delivery on screen
• sRGB– “standardized” Red / Green / Blue– optimized for screen viewing
• CMYK– Cyan / Magenta / Yellow / Black– Optimized for printing
Most library and image digitization is archived in the sRGB color space, i.e. for delivery on screen
Digital Library Leadership
Montgomery, AL ● April 20, 2004
File TypesFile Types• Raster Format
– graphic created by using a grid
• Vector Format– scalable, graphic created by mathematical
equation
• Text Format– used with OCR capture, recognizes
characters/scripts & some symbols
• Raster Format– graphic created by using a grid
• Vector Format– scalable, graphic created by mathematical
equation
• Text Format– used with OCR capture, recognizes
characters/scripts & some symbols
Digital Library Leadership
Montgomery, AL ● April 20, 2004
File Types: Raster FormatFile Types: Raster Format• GIF – “Graphic Image File”
• 256 colors; used for most web graphic design• owned by Unisys
• JPEG – “Joint Photographic Engineers Group”• can be saved using true-color or grayscale• considered to be the standard for image web display
• TIF – “Tagged Image File”• can save images as grayscale, color palette, or true-color
images• usually used for master copies of an image
• PNG – “Portable Network Graphic”• can be saved using true-color, palette, or grayscale• will supposedly replace GIFs
• GIF – “Graphic Image File”• 256 colors; used for most web graphic design• owned by Unisys
• JPEG – “Joint Photographic Engineers Group”• can be saved using true-color or grayscale• considered to be the standard for image web display
• TIF – “Tagged Image File”• can save images as grayscale, color palette, or true-color
images• usually used for master copies of an image
• PNG – “Portable Network Graphic”• can be saved using true-color, palette, or grayscale• will supposedly replace GIFs
Digital Library Leadership
Montgomery, AL ● April 20, 2004
File Types: Raster Format (examples)File Types: Raster Format (examples)
5 kbGIF
14 kbJPG
23 kbTIF
42 kbPNG
Digital Library Leadership
Montgomery, AL ● April 20, 2004
File Types: Raster Format (examples)File Types: Raster Format (examples)
32 kbGIF 111 kb
JPG 201 kbPNG 371 kb
TIF
Digital Library Leadership
Montgomery, AL ● April 20, 2004
File Types: Vector FormatFile Types: Vector Format• PDF – “Portable Document Format”PDF – “Portable Document Format”
– common format for distribution of documents common format for distribution of documents (especially magazines, journals, books, etc.)(especially magazines, journals, books, etc.)
– http://www.adobe.com/products/acrobat/main.html
• LizardTech MrSIDLizardTech MrSID– common format for distribution of maps and common format for distribution of maps and
other large image materialsother large image materials– http://www.lizardtech.com
Digital Library Leadership
Montgomery, AL ● April 20, 2004
File Types: Text FormatFile Types: Text Format• ASCII
– Most Western characters/scripts and some symbols– 8-bit coding
• UNICODE– All known world characters/scripts and almost all
symbols– 16-bit coding
ASCII will be standard, use UNICODE only as necessary to represent characters not in ASCII subset
• ASCII– Most Western characters/scripts and some symbols– 8-bit coding
• UNICODE– All known world characters/scripts and almost all
symbols– 16-bit coding
ASCII will be standard, use UNICODE only as necessary to represent characters not in ASCII subset
Digital Library Leadership
Montgomery, AL ● April 20, 2004
File Types: Text FormatFile Types: Text Format• OCR – “Optical Character Recognition”
– process used to translate graphic images into character based format
– the OCR process analyzes a document for light and dark areas in order to identify each alphabetic letter or numeric digit
– some fonts or damaged copies may cause conversion errors when rendering text
• OCR – “Optical Character Recognition”– process used to translate graphic images
into character based format– the OCR process analyzes a document for
light and dark areas in order to identify each alphabetic letter or numeric digit
– some fonts or damaged copies may cause conversion errors when rendering text
Digital Library Leadership
Montgomery, AL ● April 20, 2004
CompressionCompression• Lossless• Lossy
• Lossless• Lossy
Digital Library Leadership
Montgomery, AL ● April 20, 2004
Compression: LosslessCompression: Lossless• Retains all of the original image data• Ideal for image archiving (“off-line storage”)
– fullest possible image capture
• Ideal for viewing detail– Literally every bit of information is present
• Ideal for high-quality printing– Again, every bit of image information is present
Lossless file formats: PNG, TIF, GIF
• Retains all of the original image data• Ideal for image archiving (“off-line storage”)
– fullest possible image capture
• Ideal for viewing detail– Literally every bit of information is present
• Ideal for high-quality printing– Again, every bit of image information is present
Lossless file formats: PNG, TIF, GIF
Digital Library Leadership
Montgomery, AL ● April 20, 2004
Compression: LossyCompression: Lossy• Reduces file size by eliminating data• Ideal for “on-line storage”
– the smaller the files, the more files one can store
• Ideal for web delivery– the smaller the file, the quicker it is delivered from point
A to point B
• Acceptable for web viewing– the human eye is tolerant, it fills in the gaps– there are limits: not every lossy image can be tolerated
Lossy file formats: JPEG
• Reduces file size by eliminating data• Ideal for “on-line storage”
– the smaller the files, the more files one can store
• Ideal for web delivery– the smaller the file, the quicker it is delivered from point
A to point B
• Acceptable for web viewing– the human eye is tolerant, it fills in the gaps– there are limits: not every lossy image can be tolerated
Lossy file formats: JPEG
Digital Library Leadership
Montgomery, AL ● April 20, 2004
Acceptable Loss? B/W ExamplesAcceptable Loss? B/W Examples
315 kbJPG
0% Compression
22 kb100%
Compression
44 kb75%
Compression
79 kb50%
Compression
154 kb25%
Compression
Digital Library Leadership
Montgomery, AL ● April 20, 2004
Acceptable Loss? Color ExamplesAcceptable Loss? Color Examples
256 kbJPG
0% compression
81 kb25% compression
23 kb75% compression
39 kb50% compression
11 kb100% compression
Digital Library Leadership
Montgomery, AL ● April 20, 2004
De-Screening/Moiré RemovalDe-Screening/Moiré Removal• Moiré Effect (also called the Water Effect)
– a visual perception that occurs when a set of lines or dots that is superimposed on another set of lines or dots, where the sets differ in relative size, angle, or spacing
– in other words...
• Moiré Effect (also called the Water Effect)– a visual perception that occurs when a set
of lines or dots that is superimposed on another set of lines or dots, where the sets differ in relative size, angle, or spacing
– in other words...
Digital Library Leadership
Montgomery, AL ● April 20, 2004
Original FileFile w/ Moiré Effect Removed
De-Screening/Moiré RemovalDe-Screening/Moiré Removal
Digital Library Leadership
Montgomery, AL ● April 20, 2004
Image TouchupImage Touchup• Brightness/Contrast• Negatives• Layers• Color Settings• Slicing• Feather/Masking
• Brightness/Contrast• Negatives• Layers• Color Settings• Slicing• Feather/Masking
Digital Library Leadership
Montgomery, AL ● April 20, 2004
Brightness/ContrastBrightness/Contrast
Original Image
Adjusted Image
Digital Library Leadership
Montgomery, AL ● April 20, 2004
NegativesNegatives
Original 35mm Negative
Inverted 35mm Negative
Digital Library Leadership
Montgomery, AL ● April 20, 2004
LayersLayers
Original File File w/ added layers
Digital Library Leadership
Montgomery, AL ● April 20, 2004
Color SettingsColor Settings
Original File
File w/ adjusted input level
Digital Library Leadership
Montgomery, AL ● April 20, 2004
SlicingSlicing
Digital Library Leadership
Montgomery, AL ● April 20, 2004
Feather/MaskingFeather/Masking
Digital Library Leadership
Montgomery, AL ● April 20, 2004
Any Questions?Any Questions?
Todd Jennings Beth Nicol(334) 844-1794 (334) 844-1731jennito@auburn.edu nicollb@auburn.edu
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