Digital Reformatting of Photographic Formats Overview Aaron Choate

Digital Reformatting of Photographic Formats -Overview. Aaron Choate Digital Library Production Services The University of Texas Libraries

Photographic Format: Examples

Photographic Processes l l l Prints and Positives (Albumen prints - Tintypes) Photographic Negatives (paper, glass and film) Photographic Transparencies (glass and film)

3 x 4 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 l l l Glass Paper Plastic

Benchmarking for Conversion l l (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 l l l 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 l l l 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 l l l 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 l l l Fragile Glass Brittle/yellowing Paper Scratches on negatives Dust on slides Fading color

Document Classification l 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 l l 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 l l l 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 l l l l 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 l l l High key image’s detail is concentrated in the highlights of the document Low Key detail is in the shadows Balanced detail is evenly distributed

Ah… but it can’t be that simple l l 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 == l l l Scanning bit depth Signal-to-noise ratio Final bit depth output

Tonal accuracy l l 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 l l 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 options Bitonal l One bit per pixel Best suited for high-contrast documents (printed text)

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

color capture options Color l l l Also multiple bits per pixel (in color…) Best suited for continuous tone items with color information (RGB? CMYK? )

Bit Depth l l l 1 bit 2 colors (usually black and white) 8 bit 256 colors/shades of gray 24 bit 16 million colors/shades of gray

Measuring color l l Gretag. Macbeth – 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 l l 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! l l l 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 l l No perfect resolution for all types of material Considerations when choosing resolution for your project

Detail l l 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 l l l 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 l l l 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”x 10” from the digital file

Detail and Visual Perception l l 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 l 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

equipment Flatbed Scanners Epson 10000 XL – Graphic Artist l 2400 x 4800 dpi l 48 -bit color l 3. 8 Dmax ~$2700

equipment Flatbed Scanners l Creo – Eversmart • • 5600 dpi optical 16 bit color $30, 000 – $40, 000 All formats

equipment Film Scanners l Nikon – Coolscan 5000 ED • • 4000 dpi optical resolution 16 -bit A/D converter $1, 100 35 mm slides and negatives Film strip accessories

equipment Film Scanners l Nikon Coolscan 9000 ED • • 4000 dpi true optical resolution 16 -bit A/D converter $2000 medium format positive and negative transparencies

equipment Overhead Scanner Systems l I 2 S Digibook • • • 10000 pixel linear array RGB 200 – 800 dpi (and higher) $70, 000 All formats (with optional light box attachment)

equipment Drum scanners l 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 l Imacon Flextight 949 • • • 3 8000 pixel CCDs 80 – 8000 dpi (non-interpolated) 24, 36 & 48 bit color $20, 000

Imaging Guidelines l Image Files • Archival Master • Derivatives • Access • Thumbnail • Publication Master

imaging guidelines Master Image l l l As large as possible Uncompressed Unedited Serves as long term source for derivatives Usually stored as a TIFF

imaging guidelines What can we do to the master? Generally accepted enhancements l Reduction of greater than 8 bit/channel linear data to 8 -bit nonlinear data l Contrast stretching l Minimal adjustment for color and tone l Descreening/rescreening of halftone

imaging guidelines What can we do to the master? Debatable image processing techniques l Image sharpening l Despeckling for bitonal images l Deskewing l Software controlled color/tonal enhancements l Application of color management profiles l Conversion to CMYK or s. RGB color

imaging guidelines Access Image l l 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 guidelines Thumbnail Image l l Very small image (150 pixels on the longest dimension) Usually stored in GIF or JPEG

imaging guidelines Publication Master l l l Manipulated image that is suitable for publication High Resolution Often stored in compressed TIFF or high quality JPEG form

File formats l l Uncompressed TIFF JPEG GIF JPEG 2000 (A note about LZW compression)

software Photoshop l l (and scanner manufacturer plug-ins) or photoshop elements

software Vuescan

software Book Restorer

So then we scan…