Generally speaking, the Library reproduces pictorial items as a set of three digital images:
(1) an uncompressed archival image,
(2) a compressed reference image, and
(3) a thumbnail image.
For the first time with this collection, the Library is providing access to the uncompressed archival image as well as to the compressed reference image. By doing so, the Library hopes to serve patrons who would like a file free of the artifacts that result from the JPEG (Joint Photographic Experts Group) compression algorithm. In this case, since the archival and reference files have the same 1,200-pixel spatial resolution (see specifications below), the differences are very subtle. In the future, however, the Library will produce archival images at significantly higher resolution than the reference images. Then the archival images will have two advantages over the reference images: lack of compression artifacts and greater detail. Of course, the archival images are larger in extent (bytes) and, thus, more cumbersome to transmit and view. The Library would like to hear patron reaction to the provision of access to the archival files; please send us a note at the American Memory Help Desk.
The digital images in the presidents and first ladies reference aid were produced by scanning 8x10-inch copy negatives selected from the Prints and Photographs Division's extensive copy photograph file. (See: By Popular Demand). All but two sets of the digital images were produced by JJT, Incorporated, of Austin, Texas, which scanned the copy negatives with a Kontron digital camera.
Uncompressed Archival Images
Tonal (pixel-depth resolution): Color: 24 bits-per-pixel; black-and-white: 8 bits-per-pixel
No sharpening
Uncompressed
Tagged Image File Format (TIFF)
NOTE 1: The resolution of 1,200 pixels was selected for the digital images in this collection as consistent with the resolution planned for digital images of other copy negatives and copy transparencies. Some subsequent Library of Congress pictorial collections--especially when original materials rather than copy photographs are being digitized-- will offer archival images at resolutions of 3,000 and 5,000 pixels.
NOTE 2: Two of the archival images in this collection were carried over from another project. These are JPEG-compressed images with a spatial resolution of 3,000 pixels on the long side. These are pictures of Millard Fillmore and James Buchanan that bear the file names 3a48894v.jpg and 3b35952v.jpg, respectively.
Compressed Reference Images
Tonal (pixel-depth resolution): Color: 24 bits-per-pixel; black-and-white: 8 bits-per-pixel
Sharpened
JPEG compression to yield average compression of 10:1 for grayscale and 15:1 for color
JFIF (JPEG File Interchange Format) format/headers
Thumbnail Images
Tonal (pixel-depth resolution): 8 bits-per-pixel
Palettes optimized (adaptive palettes) for each image
Sharpened
Uncompressed
Archived copy: Tagged Image File Format (TIFF)
Online copy: GIF (Graphics Interchange Format) format, produced by the Library of Congress. These are the images displayed with the bibliographic records.
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