Guidelines for Derived JPEG Thumbnail Images
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:

File Format:

JPEG (Joint Photographic Expert Group)
Specification: ISO 10918-1/2
Reference: http://www.jpeg.org/public/jpeghomepage.htm 

Encoding:

Standard

Compression:

Minimum (highest image quality)
Not greater than 15% (image quality not less than 85% of source file)

Bit-depth:

Same as source file

DPI:

Same as source file

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.

Interpolation: Resample
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.