Negotiating the Landscape of Born-Digital Photographs (Part 1) Instructors: Stephen Fletcher & Patrick Cullom FAQs: • This live webcast will begin at 1:00 p.m. CT. • Audio will be heard through your computer or tablet’s speakers. • Submit questions for the presenters and moderator at anytime by utilizing the Q&A box. • Introduce yourself in the Chat box! • The presentation recording and slides will be made available to registrants. Request these materials by emailing [email protected]. ©2017 Society of American Archivists Stephen Fletcher Patrick Cullom North Carolina Collection Photographic Archivist Visual Materials Processing Archivist Wilson Special Collections Library Wilson Special Collections Library University of North Carolina at Chapel Hill University of North Carolina at Chapel Hill Two statements about born-digital photographs that concern me as a photographer and archivist. “An image file is just like any other file.” –A colleague “Just read dpBestflow. It has all you need to know.” –Another colleague Understanding Born- Digital Photographs as digital objects for archival processing Photographers modify and transform their image files “The medium is the message.” —Marshall McLuhan, 1964 What is a born-digital photograph? “It might seem odd, but one of the greatest difficulties in the field of digital imaging is how to identify a digital image.” –Howard E. Burdock Digital Imaging: Theory and Practice (1997) Digital Graphic vs. Digital Image A digital graphic exists only in a computer as a mathematical formula; a digital image has been imported from the real world. Or more narrowly . “A set of data that never exists as anything other than an array of pixels.” A “discreet array, usually two-dimensional, of pixels, the intensities of which are represented by numbers.” Burdock, pages 3-4 draw circle center 0.5, 0.5 Digital Graphic radius 0.4 = Vector Graphic fill-color yellow stroke-color black stroke-width 0.05 draw circle center 0.35, 0.4 radius 0.05 fill-color black draw circle center 0.65, 0.4 radius 0.05 fill-color black draw line start 0.3, 0.6 end 0.7, 0.6 stroke-color black stroke-width 0.1 Digital Image = Raster Image Image Data: The Heart of Digital Photographs The conversion of a continuous Digitization / analog sensor signal into a discrete digital representation — Quantization Michael W. Burke “The First TV Image of Mars” Mariner 4, 1965 Encoding "the process of putting a sequence of characters (letters, numbers, punctuation, and certain symbols) into a specialized format for efficient transmission or storage" Decoding "the conversion of an encoded format back into the original sequence of characters" Digital image structure Transforming continuous into discreet Any Questions on what I just covered? Photo Sensor Photo sensors detect light intensity with little or no wavelength specificity, and therefore cannot separate color information. Image Data • Proprietary data directly from sensor • “raw” • In-camera processing • usually JPEG • Raw & JPEG • Proprietary file extension, e.g., .nef for Nikon Spatial resolution camera sensor’s pixel dimensions (W x H) Common camera sensor sizes Spatial resolution • Camera sensor’s pixel dimensions (H x W) • My Pentax K-1 pixels dimensions are • 4926 x 7389 = 36398214 pixels • expressed as 36.4 megapixels (MP) Depth resolution number of bits used to hold a pixel’s value Bit depth the number of bits used to store a value Bit Depth • the number of possible values grows exponentially with the number of bits • 1-bit per pixel = bi-tonal (black or white; 0 or 255) • 8 bit = 256 tonal values per channel • JPEGs are 8-bit files • Most cameras today are 14-bit (16,384 tonal values per channel); • There are no true 16-bit cameras Pixels per Inch (PPI) vs Dots per Inch (DPI) Close, but not the same PPI DPI • INPUT or OUTPUT • OUTPUT measurement measurement • Inkjet printers place drops • Digital sensor (input) of ink (i.e. dots) on paper • • Computer monitors laser printers fuse toner (output) dots Color Filter Arrays • Color filter array (CFA) or Color Filter Mosaic (CFM) • Colored filters placed over pixel sensors to capture color information • Single filter • Bayer filter • Multi-filter • Foveon Bayer Color Filter Array Developed by Bryce E. Beyer in 1974 Patent US 3971065 A Filed March 5, 1975 by Eastman Kodak Company under the title “Color imaging array” Published July 20, 1976 Bayer Color Filter Array Demosaicing The reconstruction of a full color image from the incomplete color samples output from an image sensor overlaid with a color filter array. Unrendered & Rendered Unrendered Rendered • Raw • Has undergone • Not usable by graphics demosaicing editors (e.g., Photoshop) until rendered • e.g. Adobe Camera Raw Image File Formats The Body of Digital Photographs File Formats Structuring data Image File Format designed to store information specific to image files Types of image file formats • Unstructured formats • Chunk-based formats • Directory-based formats NDIIP National Digital Information Infrastructure and Preservation Program NDIIP "Sustainability of Digital Formats: Planning for the Library of Congress" Prehistory of image file formats File formats before TIFF The need for standards • A Standard Format for • "In 1978 the Science Digital Image Exchange Council of the AAPM • Published for the formed a Task Force to American Association of consider the problem of Physics in Medicine by the transferring digital image American Institute of data between devices. It Physics (11 March 1982), was apparent that there Report No. 10. was a growing need to make such transfers for clinical, research and service reasons." The need for standards • A Standard Format for • "The Task Force believes Digital Image Exchange that it is impractical, at • Published for the the present time, to American Association of adopt a standard internal Physics in Medicine by the representation for digital American Institute of image data acquired and Physics (11 March 1982), processed by Report No. 10. commercially available equipment." The need for standards • A Standard Format for • "The Task Force does, Digital Image Exchange however, believe that it is • Published for the possible to facilitate the American Association of transfer of data by Physics in Medicine by the defining a standard American Institute of format for exchange Physics (11 March 1982), purposes." Report No. 10. Enter TIFF • TIFF: Tagged Image File Format • Introduced by Aldus Corporation in autumn of 1986 • "Tagged" refers to file structure • Header • Followed by "chunks" of data called tags • 70+ tag types TIFF • Image header called Image File Directory (IFD) • points to one or more image file directories, which contain the image data and image information • Fixed information fields (tags) • image dimensions, color space specification, etc. then GIF • GIF: Graphic Interchange Format (1987) • Utilizes lossless compression algorithm “Lempel– Ziv–Welch" (LZW) • Limited to 256 colors or shades of gray in an image • Was proprietary: introduced by CompuServe, now all patents expired. Exif: Exchangeable image file format • Japan Electronic Industries Development Association (JEIDA) introduced Exif as an industry standard in October 1995 • Tag structure borrowed from TIFF Exif: Exchangeable image file format • Exif is a file format, BUT it’s more like a metadata schema • Cameras use Exif to record information about image format, size, resolution and color space, and optionally authoring information such as who made the image, when and where it was made, what camera model and photographic settings were used. EXIF metadata revealed by ExifTool Last login: Thu Mar 10 Interpretation : Color White Balance : Unknown (0x4) Pitch : : Auto Bracketing Assign Movie Record Shutter Count Exposure Mode Date/Time Original 11:46:57 on ttys000 Filter Array : Auto1 Toning Saturation Low AE Lock Button Button : None : 1068 : Auto : 2016:03:01 AALNCC20:~ fletches$ Strip Offsets Focus Mode : 0 No Memory Card : AE/AF Lock Fine Tune Opt Highlight Flash Info Version Digital Zoom Ratio 12:14:47.57 exiftool : 5037056 : AF-S Time Zone : Release Locked Command Dials Change Weighted: 0 : 0107 : 1 Modify Date /Users/fletches/Desktop/Samples Per Pixel Flash Setting : -05:00 ISO Display Main Sub : Autofocus Dynamic Area AF Multi Exposure Version Focal Length In 35mm : 2016:03:01 SPELLINGS\ : 1 : Daylight Savings : Show Frame Count Off, Exposure Off Display : Off : 0100 Format : 70 mm 12:14:47.57 PROTEST/_DSC0963.NRows Per Strip Flash Type : Yes Grid Display Command Dials Menu AF Point Illumination Multi Exposure Mode Scene Capture Type Circle Of Confusion EF : 4928 : Date Display Format : On And Playback : Off : On During Manual : Off : Standard : 0.030 mm ExifTool Version Strip Byte Counts White Balance Fine : D/M/Y Shooting Info Display Command Dials Focusing Multi Exposure Shots Gain Control Depth Of Field Number : 10.12 : 72737280 Tune : 0 0 ISO Expansion : Not Set Aperture Setting : Sub- Store By Orientation : 0 : None : 2.52 m (5.65 - 8.18 m) File Name X Resolution WB RB Levels : Off LCD Illumination command Dial : Off Multi Exposure Auto Contrast : Field Of View : _DSC0963.NEF : 300 : 1.95703125 ISO2 : : Off Shutter Release Button Group Area AF Gain : Off Normal : 28.6 deg (3.40 m) Directory : Y Resolution 1.26953125 1 1 100 Electronic Front-Curtain AE-L : Off Illumination : High ISO Noise Saturation Focal Length /Users/fletches/Desktop/: 300 Program Shift ISO Expansion 2 Shutter: Off Release Button To Use Squares Reduction : Normal : Normal :