| GOALS
AND OBJECTIVES
The Sanborn Fire
Insurance Company® Maps of Florida available in this collection
are the copyright deposit copies transferred from the Library of
Congress to the University of Florida. Because these were copyright
deposit copies, they exist as published, without paste-downs used
to update working copies between periodic re-publication. As such,
they represent their subject areas at exact moments in time. With
the exception of natural aging and evidence of minimal use, the
majority of these maps are in near pristine condition.
Dual goals were
set forth for imaging this collection: faithful capture of the
maps as they currently exist and digital restoration of the captured
images to emulate their original condition. Faithfully
captured images are archived and provides baseline reference for
the current restoration process as well as any subsequent restoration
projects that may be undertaken.
Faithful capture has three requirements: color-fidelity, targetted
exposure, and balance between exposure-time and noise. Color-fidelity
is achieved by color-balancing the digital camera with ANSI IT8.7/2-1993
(Graphic Technology - Color Reflection Target for Input Scanner
Calibration. Washington, D.C. : American National Standards Institute,
last revised 1993) compliant specifications through the use of targets
such as Kodak Q-60. Exposure can be varied by adjusting the lens
aperture or the capture time. Well-trained technicians, with education
in photography, can determine the color values for the 24-bit image
and the appropriate histogram distribution for each image. Balance
between exposure-time and noise entailed manipulating the digital
camera's capture sensitivity in order to obtain an efficient ISO-equivalent
capture speed without sacrificing excessive noise in the image.
Dual goals were
also set for digital restoration: approximation of original state
and color authenticity. We can never truly know the original state
of the Sanborn Fire Insurance Company® Maps
of Florida. Insufficient information is available to determine
the original reflectance of the papers on which the maps were printed.
Natural aging, acid hydrolysis, storage conditions, and use factors
have shifted not only the reflectance of the papers but of the
colors printed. Map keys, for example, describe the use of the
color "red", but what might have been red appears as pink today.
Because formulas for the production of inks is unavailable, we
do not know that the shade of red used was not closer to pink or
light red than to red as defined by ANSI IT8 compliant color calibration
target. Restoration methods attempted to return uninked
areas of the map sheets to the RGB value of white (i.e., 255 in
all channels, with a tolerance of -10 in all channels). At the
same time, restoration methods sought to retain, from the faithfully
captured images, the RGB values of black lines and of colors used
to identify building construction materials.
Users of the Sanborn
Fire Insurance Company® Maps of Florida access digitally
restorated images.
TOOLS AND PROCESSES
Image Capture
Hardware/Software
Image capture occurs through a high resolution PhaseOne Power
Phase FX+ digital camera back with a 4" x 5" capture
area that employs a 10,500 x 12,600 pixel CCD chip. The camera
back is mounted
on a planetary ZBE Satellite
universal scanning system, it includes a turreted three lens
mount with bellows, and an automated control system for calibrated
imaging. This scanning system (no longer commercially available)
has the look and feel of a commercial microfilming camera, or a
large copystand. A Rodenstock Rodagon
135 mm professional enlarging lens (f/5.6) is used in conjunction
with an AR-1 high aspect ratio filter for filtering infrared. Images
are captured via PhaseOne 3.1.1 capture software through a SCSI
PCI interface to a Macintosh Apple G4 computer operating under
OS 10 with OS 9.22 subroutines for optimal performance with the
PhaseOne imaging
software. The G4 runs at 400 MHz with 512 MB of RAM and an
18 GB SCSI
hard drive.
The
image capture area is evenly illuminated by two Videssence sRGB
fluorescent light banks each fitted with six Sylvania Daylight
Deluxe T-12 40 watt bulbs (6500K). The
maps are placed on a horizontally mounted, vertically adjustable
Cobra-Pro vacuum easel (no longer commercially available)
which is supported by two Craftsman 8.5 amp wet-dry vacuums.
ZBE Satellite System
with Phase One PowerPhase FX+
digital camera back |
 |
 |
| |
Image
Processing/Restoration Hardware
Captured images are transferred via Ethernet to an image
processing workstation, a
Macintosh Apple G4 computer operating under OS10
with a dual 1 GHz processor and 1 gigabyte of RAM. This
G4 has two hard drives: one 36 GB SCSI drive for image
processing and another 80 GB IDE drive for temporary storage
while awaiting archiving to CD-rom.
Image Processing/Restoration
Software
Adobe Photoshop is used to process images. In addition to the
extensive editing features of this software program,
Photoshop is used for the added efficiency of the Actions
feature. This feature allows exactly the same set of editing
actions to be applied to batches of images. In this
instance, an Action was specifically tailored for this
project and the common characteristics of the Maps
of Florida. This action was devised to obtain the
specific restoration objectives while minimizing operator
intensive restoration. In effect, much of the restoration
needed can be automated. Batches were scheduled to run
overnight, unattended, to increase project efficiency
and reduce labor costs. Once the images are processed
they are checked for quality. Further restoration, or
adjusted reprocessing is done at the operator’s discretion
in respect to line quality, color accuracy, and the overall
quality of the restoration. All images, both the processed
(i.e., digitally restored) and unprocessed (i.e., faithfully
captured), are are saved in the uncompressed TIFF file
format to an intermediary gold-based CD-ROM archive.
Image Characteristics
The Sanborn Map Collection was captured as 24-bit (16
million colors) RGB Phaseone TIFF files with a Macintosh
byte order. The uncompressed ITU TIFF(v.6) files are converted
to a IBM PC byte order TIFF during batch processing. The
uncompressed TIFF file sizes range from 120-144 MB due
to variances of the particular days setup and variance
in paper sizes. The variance in paper sizes is generally
less than ˝ inch between editions,
and 21" x 25" would be considered standard. At this size,
with 1:1 magnification, the captures are approximately
6300 x 7500 pixels in dimension at a resolution of 300
pixels per square inch.
|
|
Image Characteristics
Summary
|
|
| Souce
Document Size: |
21" x
25" |
| Resolution: |
300
ppi |
| Magnification: |
100%
(1:1) |
| Area
Captured by Image: |
6300
x 7500 pixels |
| Average
File Size: |
120-144
MB |
| Color-Space: |
sRGB |
| Bit-Depth: |
24-bit |
| File
Format: |
ITU
TIFF, v.6
uncompressed |
|
|
DIGITALLY
RESTORED IMAGES
|
| Souce
Document Size: |
21" x
25" |
| Resolution: |
300
ppi |
| Magnification: |
100%
(1:1) |
| Area
Captured by Image: |
6300
x 7500 pixels |
| Average
File Size: |
120-144
MB |
| Color-Space: |
sRGB |
| Bit-Depth: |
24-bit |
| File
Format: |
ITU
TIFF, v.6
uncompressed |
|
Post-Processing (SID File Generation)
Processed files are transferred via Ethernet to a workstation running
Windows 2000, where they are compressed for delivery via the Internet. The
workstation is a Pentium 4 processor operating at 1400 MHz, 768 MB
of RAM, and an 80 GB IDE hard drive. The software used for compression
is Lizardtech’s
MrSid Geospatial Encoder, version 1.3.1. The images are
compressed with a target compression of 20, a zoom level of 4, and
a target thumbnail of 500
pixels in width. After a quality inspection, the compressed images
and TIFF files are transferred to the Florida Center for Library
Automation (FCLA) for digital archiving and
Internet delivery. SID files can be accessed from the SID server
without installation of an Internet browser plugin. |
