Summary:
These Guidelines indicate requirements for web-deliverable
thumbnail JPEG image files created for PALMM Visual Collections projects.
JPEG thumbnails correspond to larger display images in JPEG 2000 or SID scaleable format.
Specifications:
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File Format: |
JPEG (Joint Photographic Expert Group)
Specification: ISO
10918-1/2
Reference: http://www.jpeg.org/public/jpeghomepage.htm |
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Encoding: |
Standard |
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Compression: |
Minimum (highest image quality)
Not greater than 15% (image quality not
less than 85% of source file)
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Bit-depth: |
Same as source file |
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DPI: |
Same as source file |
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Image Dimensions: |
Width = 100 pixels; Height = variable
Maintain original image aspect ratio
Note: JPEG Thumbnails for PALMM Visual Collections are used by patrons to select larger, zoomable images. For this reason, the thumbnail may highlight a significant aspect of the larger image rather than the entire image in totality. |
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Interpolation: |
Resample |
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File Header: |
Append structured information about the derivation process as
appropriate to the SUSDL XML Metadata DTD (forthcoming)
A structured information template will
be added in a future revision of these Guidelines |
Process:
No single method of processing is recommended.
Quality Control:
A visual inspection together with a
query of the file header should be completed by spot check. Spot check
requires inspection of every image in thumbnail view and of no less than 10%
of the images in full-image view.
A variety of factors effecting on-screen
and print legibility should be examined. For additional guidance,
we recommend reading Cornell University's Digital
Imaging Tutorial: Quality Control.
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