Each poster in the WPA collection has been copied onto slide film to facilitate photographic reproduction orders and to reduce handling of the posters themselves. The slides were scanned to provide digital images for this online collection.
About one-third of the slides were digitized in the early 1990s to create an analog videodisc which was used as a reference aid in the Prints and Photographs Division. These slides were first photographed onto an intermediate negative film and then digitized to approximately 1500 pixels in the long dimension. For these posters, a thumbnail image, a 640-pixel JPEG format image, and the uncompressed archival image are available for viewing and downloading.
The remaining slides were digitized to approximately 4000 pixels in the long dimension by JJT, Inc. of Austin, Texas in the summer of 2000. Because these uncompressed archival images are so much larger, an additional 1024-pixel JPEG format image is available to facilitate display of small details.
Specifications For This Collection
| Uncompressed Archival Images | |
|---|---|
| Spatial resolution: | Approximately 1500 or 4000 pixels on the long side with the short side scaled in proportion. |
| Tonal (pixel depth) resolution: | 24 bits per pixel (RGB color). |
| Image enhancement: | None. |
| File format: | Tagged Image File Format (TIFF) ver. 6.0. |
| Compression: | None. |
Compressed Service Images | |
| Spatial resolution: | About 640 pixels on the long side with the short side scaled in proportion. An additional 1024-pixel set of service images exists for some of the collection. |
| Tonal (pixel depth) resolution: | 24 bits per pixel. |
| Image enhancement: | Mild sharpening. |
| File format: | JFIF (JPEG File Interchange Format). |
| Compression: | JPEG at a quality setting that yields an average compression of 15:1 for the 640-pixel images. Compression is approximately 8:1 for the 1024-pixel images. |
Thumbnail Images | |
| Spatial resolution: | About 150 pixels on the long side with the short side scaled in proportion. |
| Tonal (pixel depth) resolution: | 8 bits per pixel; palettes optimized (adaptive palettes) for each image. |
| Image enhancement: | Sharpened. |
| File formats: | Archived copy: TIFF--Tagged Image File Format
Online copy: GIF--Graphics Interchange Format |
| Compression: | Archived copy: Uncompressed.
Online copy: Compression native to the GIF format. |