Digital Reformatting of Photographic Formats-Overview-Aaron ChoateDigital Library Production ServicesThe University of Texas Libraries

Photographic Format: Examples

Photographic ProcessesPrints and Positives (Albumen prints - Tintypes)Photographic Negatives (paper, glass and film)Photographic Transparencies (glass and film)

3x4House typical to the Latin-American section of town. Corpus Christi, Texas. -- Russell Lee

The Center for American History

35 mm negativeStudents in the auto repair and painting class at Del Mar College. Corpus Christi, Texas. -- Russell Lee

The Center for American History

35 mm slideMarian Davis Slide CollectionSchool of Architecture Visual Resources Collection

MountsGlassPaperPlastic

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 propertiesWhat 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 PerceptionSubjective 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 presentationWhat 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 conditionFragile GlassBrittle/yellowing PaperScratches on negativesDust on slidesFading color

Document ClassificationPhotographs are continuous tone materialTone and color reproduction become just as important or more so than detailAlways scan at multiple bitsBit depths greater than or equal to 8 per channel are suggested by most imaging guidelines

Medium and supportHow does the glass, paper or film affect the representation of the item in digital form.Do you want to capture or minimize the supports physical properties.

Tonal RepresentationDynamic 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 portionThe higher the dynamic range, the more potential shades can be represented.

Typical Dynamic Ranges for source documentsNewsprint -- .9Printed material 1.5Coated stock 1.5 1.9Photographic prints 1.4 2.0Negative films 2.8Commercial color slides 2.8 3.0High grade transparencies 3.0 4.0

Key typeHigh key images detail is concentrated in the highlights of the documentLow Key detail is in the shadowsBalanced detail is evenly distributed

Ah but it cant be that simpleScanner data on dynamic range isnt always reliableBit-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 depthSignal-to-noise ratioFinal bit depth output

Tonal accuracyYou 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 AppearanceIs color reproduction necessary to the documents meaning?What is the nature of the color?What purpose does the color serve?How important is maintaining the color appearance?

Color capture optionsOmar PashaHelmolt, H.F., ed. History of the World. New York: Dodd, Mead and Company, 1902.

color capture optionsBitonalOne bit per pixelBest suited for high-contrast documents(printed text)

color capture optionsGrayscaleMultiple bits per pixel (shades of gray)Best suited for continuous tone (B&W) documents such as photographs

color capture optionsColorAlso multiple bits per pixel (in color)Best suited for continuous tone items with color information(RGB? CMYK?)

Bit Depth1 bit 2 colors (usually black and white)8 bit 256 colors/shades of gray24 bit 16 million colors/shades of gray

Measuring colorGretagMacbeth 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-wiseCalibrate your scanning device to a color standardCalibrate the rest of the imaging system to the scannerControl your lighting environment (same levels for production and evaluation)Scan grayscale and color targets with each image or production batch

But wait theres more!Stay close to the scanning devices capabilities and try to make only minor corrections to the master imagesConsider capturing at greater than 8 bits/channelSave the image in RGB with International Color Consortium profilesSave the image as a TIFF and preserve the color profile infoMaintain scanning-related metadata

ResolutionNo perfect resolution for all types of materialConsiderations when choosing resolution for your project

DetailMeasure 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 strokewidth of the finest line, stroke of dot, or marking that must be captured in the digital surrogateThe finest feature should be covered by at least 2 pixels for it to be properly representedA feature at 1/100 inch would require 200 dpi to be properly depicted

Detail as ScaleDominant 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 8x10 from the digital file

Detail and Visual PerceptionAdding 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

Equipment - examples

equipmentFlatbed ScannersEpson 10000XL Graphic Artist2400 x 4800 dpi48-bit color 3.8 Dmax ~$2700

equipmentFlatbed ScannersCreo Eversmart5600 dpi optical16 bit color$30,000 $40,000

All formats

equipmentFilm ScannersNikon Coolscan 5000 ED4000 dpi optical resolution16-bit A/D converter

$1,100

35 mm slides and negativesFilm strip accessories

equipmentFilm ScannersNikon Coolscan 9000 ED4000 dpi true optical resolution 16-bit A/D converter

$2000

medium format positive and negative transparencies

equipmentOverhead Scanner SystemsI2S Digibook10000 pixel linear arrayRGB200 800 dpi (and higher)

$70,000

All formats (with optional light box attachment)

equipmentDrum scannersICG 380 Drum Scanner12,000 dpiCMYK-on-the-fly at drum speeds of up to 1800 rpm

$50,000

equipmentVirtual Drum ScannerImacon Flextight 9493 8000 pixel CCDs80 8000 dpi (non-interpolated)24, 36 & 48 bit color $20,000

Imaging GuidelinesImage FilesArchival MasterDerivativesAccessThumbnailPublication Master

imaging guidelinesMaster ImageAs large as possibleUncompressedUneditedServes as long term source for derivativesUsually stored as a TIFF

imaging guidelinesWhat can we do to the master?Generally accepted enhancementsReduction of greater than 8 bit/channel linear data to 8-bit nonlinear dataContrast stretchingMinimal adjustment for color and toneDescreening/rescreening of halftone

imaging guidelinesWhat can we do to the master?Debatable image processing techniquesImage sharpeningDespeckling for bitonal imagesDeskewingSoftware controlled color/tonal enhancementsApplication of color management profilesConversion to CMYK or sRGB color

imaging guidelinesAccess ImageGenerally fits within the viewing area of a computer monitor (1024 x 768)Files sized for fast downloadCompressed for access speedUsually stored in JPEG format

imaging guidelinesThumbnail ImageVery small image (150 pixels on the longest dimension)Usually stored in GIF or JPEG

imaging guidelinesPublication MasterManipulated image that is suitable for publicationHigh Resolution Often stored in compressed TIFF or high quality JPEG form

File formatsUncompressed TIFFJPEGGIFJPEG2000 (A note about LZW compression)

softwarePhotoshop(and scanner manufacturer plug-ins) or photoshop elements

softwareVuescan

softwareBook Restorer

So then we scan