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Digital Imaging Process, Phase 1

The text below describes some technical aspects of workflow and operating procedures used in a previous phase of the DAC Digital Imaging Initiative. We are currently using a new image capture setup with a Better Light 6000 E-HS digital scanning back, Cambo 4x5 Repro camera, and Schneider Macro-Symmar lenses in ways described on another page.

DAC imaging setup

In the first direct-capture phase of the imaging initiative, each object to be imaged was placed on a copy stand equipped with four 60-Watt halogen lamps. These lamps illuminated the work at a light level of about 100 foot-candles. Sheets of ultraviolet-filtering plexiglas in front of the lamps protected the objects from UV light.

The total duration of light exposure each object received was on the order of 20 to 40 seconds for objects in series with consistent dimensions, and up to several minutes in other cases. While 100 foot-candles would be far too high a light level for prolonged exposure for works of art on paper, it's safe for such a brief period of time.

The images were made with a Fuji DS-300 digital camera that yields 1280 x 1000 pixel uncompressed, raw capture files. White balance, aperture, and exposure time were set manually using procedures developed through quantitative measurement and trial-and-error experimentation. The camera was set to auto-focus. Framing and alignment were set roughly by real-time viewing on a small video monitor, and adjusted and re-shot if necessary after viewing transferred files on a computer monitor.

Image files were transferred from the camera to a Macintosh PowerPC 7200 via a SCSI PC card reader. (We began the project using a 115kbps serial interface. Because each 5-minute file transfer tied up both the camera and the Mac, this proved to be a major speed bottleneck for capture-session workflow. Along with a second memory card, the reader allowed us to keep the camera and CPU in much more efficient cycles of use.)

All images were captured, processed, and served in color (even those of "black and white" images) in order to convey important subtleties of paper and ink tone, often crucial to communicating a sense of the original work.

Images were processed with Adobe Photoshop and other applications to perform baseline corrections. A few images required rotating (up to about 0.4 degrees, with bicubic interpolation) to compensate for minor misalignment at time of capture. Each image was then cropped to the area we wished to use (usually with a small margin around the original object's image area), and enhanced slightly for sharpness. Then adjustment layers were added for color balance, saturation, and tonal range (illustrated on the rough calibration page for that phase of the project).These standard corrections were followed by individual fine-tuning, often with direct comparison to original objects.

After processing, each image was saved as a cropped Photoshop file with undoable adjustment layers. Four progressive JPEGs were exported using the HVS JPEG plug-in (with Q set to 84) at sizes tailored to the DAC's database and web projects: maximum height or width of 108 and 560 pixels for the web, 216 and 960 pixels for the database). Along with reference images of color control patches and gray scale, all files were archived to 230MB magneto-optical disks; JPEGS were also copied elsewhere for active use.

The images' maximum dimension of 560 pixels allows them to be viewed in full on monitors set to at least 832 x 624 pixels, provided the viewer's browser window is maximized and has all of its button and location bars hidden. Image production for monitors of this resolution strikes a balance between serving users with large and not-so-large screens, while providing enough detail for study purposes in a digital file of reasonable size (i.e., for storage space and transfer time to clients).