A.1.6 Sample Item PD2

To view an image, click on the appropriate link (after noting the size and inferring its potential Internet transfer time). In most web browsers, to download the same file for local use, right-click on the same link and choose "Save Link As..." or a similar command. In general, the "full size" images are most suited for downloading and closer analysis; the screen width images are intended only for Internet access.

Sizes are given for full size images for purposes of comparison between the different image formats. The sizes of screen width images, however, are given only to allow network transfer time to be estimated. These sizes are given in parentheses.

Original 8-bit Grayscale, No Contrast Stretch

Screen width as an interlaced GIF (142 KB)
Thumbnail of original grayscale
Thumbnail of Original
as a progressive JPEG, no contrast stretch
Full size as a grayscale TIFF 8510 KB

All of the images below have been contrast stretched. Without this, some of the originals are extremely dark and of low contrast. To get an accurate sense of the inherent difficulty in imaging some of these pages, it is important to have a look at the original.

Three different JPEG compression levels are shown in the next three tables. The precise meaning (or even the name) of the parameter "quality level" is specific to a given piece of JPEG software; it has no absolute meaning, but is a relative measure of how highly compressed an image is. Compression ratio is the only useful absolute measure.

Several screen width viewing copies of the "quality level" = 50 JPEG file have been prepared for presentation here.

The full size JPEG is in sequential JPEG form as are all the Phase II production images. A means exists to convert a sequential to a progressive JPEG losslessly, provided both are the same size. This was not done here, since the purpose of the full size image is to permit close inspection of the final resolution image. While it is a slow process, sequential display (or downloading) is better for this purpose.

JPEG "Quality Level" = 50

Compression ratio: 14.1 to 1
Thumbnail of JPEG, quality level 50
Thumbnail of JPEG
as a progressive JPEG
Screen width as a progressive JPEG (42 KB)
Screen width as a sequential JPEG (41 KB)
Full size as a sequential JPEG 602 KB

No thumbnails or screen width images are provided for the following two JPEG files, since they would be indistinguishable from the set just above.

JPEG "Quality Level" = 40

Compression ratio: 11.2 to 1
Full size as a sequential JPEG 763 KB

JPEG "Quality Level" = 30

Compression ratio: 8.1 to 1
Full size as a sequential JPEG 1050 KB

Binarized, 1-Bit per Pixel

Screen width as a "scale to gray" (anti-aliased), interlaced GIF (55 KB)
Thumbnail of Binarized
as an anti-aliased GIF
Full size as a Group 4 compressed binary TIFF 84 KB
Full size as a two color binary GIF 151 KB

 

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