The ethnic images in the John and Selma Appel collection represent a variety of media--political cartoons, postcards, sheet music books, and so on. The digital images in this online collection have been produced from high-quality 35mm photographic slides of the originals.
Slides were scanned at an optical resolution of 1350 dpi using the Nikon LS-2000 Film Scanner. The captured images were then processed to create a set of three images for each item: a high-resolution archival copy, a good-quality reference copy (as seen in the exhibit), and a small, low resolution thumbnail copy.
The following technical standards apply to the digital images in the collection:
Archival Images: Spatial resolution of approximately 1800 pixels on the long side of the image, with the short side falling where it may. Pixel depth of 24 bits/pixel. Tagged Image File Format (TIFF), with no compression, sharpening, or other processing other than color correction.
Reference Images: Spatial resolution of approximately 640 pixels on the long side of the image, with the short side falling where it may. Pixel depth of 24 bits/pixel (color images) or 8 bits/pixel (greyscale). Images are compressed at an average ratio of 10:1 in the JPEG format. Reference images have been digitally "sharpened" to compensate for the loss of resolution required for a web-based presentation.
Thumbnail Images: Spatial resolution of approximately 150 pixels on the long side of the image, with the short side falling where it may. Pixel depth of 8 bits/pixel with an adaptive color palette. GIF-native compression is used, and images are sharpened to improve appearance.