Compression Types

Imaging ActiveX controls support the following compression types:

RBA (read-only) The RBA compression type is used to compress black-and-white AWD (At Work Document) images.  RBA is a Microsoft-proprietary compression type.

Group3(1D) A compression type based on the CCITT Group3 fax standard, Group3(1D) is used to compress black-and-white TIFF image document files.  Group3(1D) encodings are designed to provide reliable delivery of image data over inherently unreliable data links.  It is commonly used to compress images for fax transmission.

Group3(2D) (read-only) Similar to the Group3(1D) compression type, Group3(2D) is used to compress black-and-white TIFF image document files for fax transmission exclusively.  Group 3(2D) encodings provide a high degree of error recovery during fax transmission.

Group3(Modified Huffman [MH]) Group3(MH) is also used to compress black-and-white TIFF image document files.  Group3(MH) encodings are designed to provide reliable delivery of image data over inherently unreliable data links.  It differs from Group3(1D) in that it provides increased compression.

Group4(2D) Based on the CCITT Group4 fax standard, Group4(2D) is used to compress black-and-white TIFF image document files saved to disk, or sent as faxes or e-mail messages over reliable data links, such as ISDN or X.25.  It provides superior compression for non-dithered images when compared to the Group3(1D) compression type.

JPEG The Joint Photographics Experts Group compression type is used to compress 24-bit color (RGB24) and 8-bit gray-scale (Gray8) TIFF image document files.  JPEG produces a high compression ratio, but some image data is actually lost during compression.

JPEG is a lossy compression type, which means that some data is altered and lost during compression.  Most of the time, data alteration and loss are not significant.  Lossy compression types typically offer higher compression ratios than do lossless compression types.

When using the JPEG compression type, JPEG compression options can also be specified.  These options determine the overall quality of image documents and the storage space they require.

LZW (Lempel-Ziv-Welch) The LZW compression type compresses TIFF image documents of any page type (except black-and-white).  It is a lossless compression type, which means that no data is altered or lost during compression.  Lossless compression types typically offer lower compression ratios than do lossy compression types.

PackBits PackBits is used to compress black-and-white TIFF image documents for any purpose.  PackBits is a simple, byte-oriented run-length compression scheme that has a good worst-case behavior.

PCX (read-only) A ZSoft-proprietary compression type, PCX is used to compress multipage DCX and single-page PCX black-and-while and color images.

Xerox-proprietary (read-only) The Xerox-proprietary compression type is used to compress XIF images.