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Preservation Services : Digitization services : Digital image options

Digitizing: Digital image options

OCLC Preservation Service Centers deliver digital images in a variety of file formats. The most common format is TIFF (Tagged Image File Format), but we can also supply JPEG (Joint Photographic Experts Group) and GIF (Graphics Interchange Format) formats.

Bitonal TIFF files include uncompressed, ITU (formerly CCITT) Group 4 compression or ITU Group 3 compression. Both Group 3 and Group 4 compression are lossless. The more prevalent Group 4 realizes a higher compression.

OCLC Preservation Service Centers can also deliver grayscale files as uncompressed or with lossless LZW (Lempel-Ziv-Welch) compression, or other files with lossy compression, such as JPGs.

Lossy compression algorithms reduce image size by discarding information that is not easily perceptible to the human eye and can be adjusted to degrees of quality or loss with a quality factor.

Derivative images can be resized to accommodate onscreen viewing and quick access for browsing: According to client specifications we reduce image dimensions, resolution or bit depth to create "thumbnails" or other file types that are requested for various online access models.

Delivery media options

Most files are delivered on single-session CD-Rs written to ISO-9660 standards. Delivery options include CD-R, DVD+R, and tapes including LTO and DLT. In addition, images may be transferred by FTP to your location or to OCLC Preservation Service Centers' FTP site for pickup.