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Digital Reformatting of Photographic Formats-Overview- Aaron Choate Digital Library Production Services The University of Texas Libraries
Photographic Processes • Prints and Positives(Albumen prints - Tintypes) • Photographic Negatives(paper, glass and film) • Photographic Transparencies(glass and film)
3x4 House typical to the Latin-American section of town. Corpus Christi, Texas. -- Russell Lee The Center for American History
35 mm negative Students in the auto repair and painting class at Del Mar College. Corpus Christi, Texas. -- Russell Lee The Center for American History
35 mm slide Marian Davis Slide Collection School of Architecture Visual Resources Collection
Mounts • Glass • Paper • Plastic
Benchmarking for Conversion • (pages 27 – 60 of Moving Theory into Practice) • Even after the issue has been identified and studied, the problem of benchmarking digital imaging systems remains open.
Physical properties • What is it about the original that you are trying to capture? • In many cases it is possible to capture the grains of the emulsion on the film. • Is this necessary for the project to be successful?
Visual Perception • Subjective comparison between a digital print and an otherwise reformatted object may lead you to decide that you only need the digital version to be legible. • How much is enough… how much is too much. • What is enough for the items that you are working with?
Physical Type, size and presentation • What equipment will you need to use to fit the object? • How large a file will you be dealing with? • Can these items be bulk processed?
Physical condition • Fragile Glass • Brittle/yellowing Paper • Scratches on negatives • Dust on slides • Fading color
Document Classification • Photographs are continuous tone material… • Tone and color reproduction become just as important or more so than detail • Always scan at multiple bits • Bit depths greater than or equal to 8 per channel are suggested by most imaging guidelines
Medium and support • How does the glass, paper or film affect the representation of the item in digital form. • Do you want to capture or minimize the support’s physical properties.
Tonal Representation • Dynamic Range –the range of tonal difference between the lightest light and the darkest dark. • Range from 0 – 4 with the lightest portion being potentially 10,000 brighter than the darkest portion • The higher the dynamic range, the more potential shades can be represented.
Typical Dynamic Ranges for source documents • Newsprint -- .9 • Printed material – 1.5 • Coated stock – 1.5 – 1.9 • Photographic prints – 1.4 – 2.0 • Negative films – 2.8 • Commercial color slides – 2.8 – 3.0 • High grade transparencies – 3.0 – 4.0
Key type • High keyimage’s detail is concentrated in the highlights of the document • Low Keydetail is in the shadows • Balanceddetail is evenly distributed
Ah… but it can’t be that simple • Scanner data on dynamic range isn’t always reliable • Bit-depth only loosely correlates with tonal resolution because the upper bits of most scanning devices carry a declining percentage of reliable information
Tonal reproduction == • Scanning bit depth • Signal-to-noise ratio • Final bit depth output
Tonal accuracy • You have determined that your scanner can reproduce the tonal range, but will it map them properly? • Using a grayscale target will allow you to anchor your “aimpoints” to a source with known digital values
Color Appearance • Is color reproduction necessary to the document’s meaning? • What is the nature of the color? • What purpose does the color serve? • How important is maintaining the color appearance?
Color capture options Omar Pasha Helmolt, H.F., ed. History of the World. New York: Dodd, Mead and Company, 1902.
color capture optionsBitonal • One bit per pixel • Best suited for high-contrast documents • (printed text)
color capture optionsGrayscale • Multiple bits per pixel (shades of gray) • Best suited for continuous tone (B&W) documents such as photographs
color capture optionsColor • Also multiple bits per pixel (in color…) • Best suited for continuous tone items with color information • (RGB? CMYK?)
Bit Depth • 1 bit2 colors (usually black and white) • 8 bit256 colors/shades of gray • 24 bit16 million colors/shades of gray
Measuring color • GretagMacbeth – color evaluation system that could be adapted to digital imaging programs. • Most reports on digitization of cultural resources confirms the difficulty and frustration of capturing and presenting color that approximates the original
So what can we do color-wise • Calibrate your scanning device to a color standard • Calibrate the rest of the imaging system to the scanner • Control your lighting environment (same levels for production and evaluation) • Scan grayscale and color targets with each image or production batch
But wait there’s more! • Stay close to the scanning device’s capabilities and try to make only minor corrections to the master images • Consider capturing at greater than 8 bits/channel • Save the image in RGB with International Color Consortium profiles • Save the image as a TIFF and preserve the color profile info • Maintain scanning-related metadata
Resolution • No perfect resolution for all types of material • Considerations when choosing resolution for your project
Detail • Measure the finest scale of line that should be represented in the digital image. (telephone line, individual hair) • Film formats should be measured using magnification
Detail as stroke • width of the finest line, stroke of dot, or marking that must be captured in the digital surrogate • The finest feature should be covered by at least 2 pixels for it to be properly represented • A feature at 1/100 inch would require 200 dpi to be properly depicted
Detail as Scale • Dominant scale – the distance covered by the most significant structural feature(ie: knots in a carpet) • How granular do you get? Can we capture the film grain? Do we want to? • Some institutions base their decision on what it would take to print an 8”x10” from the digital file
Detail and Visual Perception • Adding dpi and bit-depth increases the amount of accuracy to a point, but at some point you reach a level of diminishing returns. • 400 – 600 dpi for most visible structures in printed text or images should be fine. (slides and transparencies will require higher resolutions)
Testing the scanners performance • Modulation Transfer Function (MTF) • Potentially correlates known details (frequencies) and how well the system detects the details. • There has been a great deal of work on this and a product called Imatest has incorporated it into the tests it will run on your camera
equipmentFlatbed Scanners Epson 10000XL – Graphic Artist • 2400 x 4800 dpi • 48-bit color • 3.8 Dmax ~$2700
equipmentFlatbed Scanners • Creo – Eversmart • 5600 dpi optical • 16 bit color $30,000 – $40,000 All formats
equipmentFilm Scanners • Nikon – Coolscan 5000 ED • 4000 dpi optical resolution • 16-bit A/D converter $1,100 35 mm slides and negatives Film strip accessories
equipmentFilm Scanners • Nikon Coolscan 9000 ED • 4000 dpi true optical resolution • 16-bit A/D converter $2000 medium format positive and negative transparencies
equipmentOverhead Scanner Systems • I2S Digibook • 10000 pixel linear array • RGB • 200 – 800 dpi (and higher) $70,000 All formats (with optional light box attachment)
equipmentDrum scanners • ICG 380 Drum Scanner • 12,000 dpi • CMYK-on-the-fly at drum speeds of up to 1800 rpm $50,000
equipment“Virtual” Drum Scanner • Imacon Flextight 949 • 3 8000 pixel CCDs • 80 – 8000 dpi (non-interpolated) • 24, 36 & 48 bit color$20,000
Imaging Guidelines • Image Files • Archival Master • Derivatives • Access • Thumbnail • Publication Master
imaging guidelinesMaster Image • As large as possible • Uncompressed • Unedited • Serves as long term source for derivatives • Usually stored as a TIFF
imaging guidelinesWhat can we do to the master? Generally accepted enhancements • Reduction of greater than 8 bit/channel linear data to 8-bit nonlinear data • Contrast stretching • Minimal adjustment for color and tone • Descreening/rescreening of halftone
imaging guidelinesWhat can we do to the master? Debatable image processing techniques • Image sharpening • Despeckling for bitonal images • Deskewing • Software controlled color/tonal enhancements • Application of color management profiles • Conversion to CMYK or sRGB color
imaging guidelinesAccess Image • Generally fits within the viewing area of a computer monitor (1024 x 768) • Files sized for fast download • Compressed for access speed • Usually stored in JPEG format
imaging guidelinesThumbnail Image • Very small image (150 pixels on the longest dimension) • Usually stored in GIF or JPEG
imaging guidelinesPublication Master • Manipulated image that is suitable for publication • High Resolution • Often stored in compressed TIFF or high quality JPEG form