ImageGear for C and C++ on Windows v19.4 - Updated
IG_ISIS_TAG_COMPRESSION
API Reference Guide > ISIS Component API Reference > ISIS Component Tags Reference > Data Format Tags > IG_ISIS_TAG_COMPRESSION

Data compression. 0x0103  259

IG_ISIS_TAG_COMPRESSION allows you to set or determine the compression being used by a scanner.

Type:

IG_ISIS_TAG_TYPE_SHORT

Drivers:

All source and destination drivers.

Values:

The application must get choices (using IG_ISIS_choice_get_long) to be aware of the number of possible compression settings available in a scanner. Most scanners either return uncompressed only or uncompressed and Group 4 compressed data. To determine the compression format that exists in a file or other image data, use IG_ISIS_tag_get_long. The following values define the various compression choices that were available when this manual was last revised:

1 IG_ISIS_COMPRESSION_NONE No compression, each line is packed to one byte.
2 IG_ISIS_COMPRESSION_MG3 Modified (no EOL) CCITT Group 3 1-Dimensional Huffman run-length encoding, each line starts on a new byte. BitsPerSample and SamplesPerPixel must be 1, since this type of compression is defined only for binary images.
3 IG_ISIS_COMPRESSION_G3 Standard CCITT Group 3 coding, 1 Dimensional Huffman run-length encoding. BitsPerSample and SamplesPerPixel must be 1, since this type of compression is defined only for binary images.
4 IG_ISIS_COMPRESSION_G4 Standard CCITT Group 4 encoding. BitsPerSample and SamplesPerPixel must be 1, since this type of compression is defined only for binary images.
5 IG_ISIS_COMPRESSION_LZW LZW coding as described in the TIFF specification.
6 IG_ISIS_COMPRESSION_JPEG JPEG coding typically used for grayscale and color only.
32771 IG_ISIS_COMPRESSION_32771 No compression, each line padded to two bytes. (Erroneously called IG_ISIS_ COMPRESSION_N16 in previous documentation.)
32773 IG_ISIS_COMPRESSION_PACK Packbits compression.
34661 IG_ISIS_COMPRESSION_JBIG JBIG compression, typically used for binary and grayscale only and returned by very few scanners, is a lossless multi-plane compression format that yields high compression for most business documents. This data can be written to a TIFF file that can be uncompressed and converted into another format.
50000 IG_ISIS_COMPRESSION_PCX Compression scheme used in PCX files.
50001 IG_ISIS_COMPRESSION_4BYTE No compression, each line padded to four bytes.
50002 IG_ISIS_COMPRESSION_RUN Runlist compression; internal use only.
50005 IG_ISIS_COMPRESSION_GIF Compression scheme used in GIF files.
50006 IG_ISIS_COMPRESSION_BMP Compression scheme used in BMP files.
50007 IG_ISIS_COMPRESSION_RUNBLOCK A block of runlists; internal use only.
50014 IG_ISIS_COMPRESSION_WANGJPEG Wang format JPEG encoding, typically used for grayscale and color only.

Tag Dependencies and Dependent Tags:

Some scanner drivers may reset the value of IG_ISIS_TAG_COMPRESSION based on the values of the color format tags. For example, it does not make sense to use JPEG compression on a binary PCX file, because there are no applications that will open such a file. Therefore, you should be sure to set IG_ISIS_TAG_COMPRESSION after setting the desired color format.

IG_ISIS_TAG_SAMPLESPERPIXEL  IG_ISIS_TAG_BITSPERSAMPLE  IG_ISIS_TAG_PHOTOMETRICINTERPRETATION  IG_ISIS_TAG_COMPRESSION

See Also

IG_ISIS_TAG_BITSPERSAMPLE

IG_ISIS_TAG_SAMPLESPERPIXEL

IG_ISIS_TAG_PHOTOMETRICINTERPRETATION