ICAP_COMPRESSION

Description

Allows the application and Source to identify which compression schemes they have in common for Buffered Memory and File transfers.

Note for File transfers:

Since only certain file formats support compression, this capability must be negotiated after setting the desired file format with ICAP_IMAGEFILEFORMAT.

TWCP_NONE All Sources must support this. TWCP_PACKBITS Can be used with TIFF or PICT TWCP_GROUP D, TWCP_GROUP DEOL, TWCP_GROUP D, TWCP_GROUP Are all from the CCITT specification (now ITU), intended for document images (can be used with TIFF).

TWCP_JPEG Intended for the compression of color photographs (can be used with TIFF, JFIF or SPIFF).

TWCP_LZW A compression licensed by UNISYS (can be used with TIFF).

TWCP_JBIG Intended for bitonal and grayscale document images (can be used with TIFF or SPIFF).

TWCP_PNG This compression can only be used if ICAP_IMAGEFILEFORMAT is set to TWFF_PNG.

TWCP_RLE ,

TWCP_RLE ,

TWCP_BITFIELDS These compressions can only be used if ICAP_IMAGEFILEFORMAT is set to TWFF_BMP.

TWCP_ZIP Per RFC 1951 (AKA 'Flate' and 'Deflate')

TWCP_JPEG Per ISO/IEC 15444

Application

Applications must not assume that a Source can provide compressed Buffered Memory or File transfers, because many cannot. The application should use MSG_SET on a TW_ONEVALUE container to specify the compression type for future transfers.

Source

Values

The current value of this setting specifies the compression method to be used in future transfers. If the image transfer mechanism is changed, then the allowed list must be modified to reflect the supported values. If the current value is not available on the new allowed list, then the Source must change it to its preferred value.

Type: TW_UINT

Value after MSG_OPENDS: (may be remembered from a previous session)

After MSG_RESET/MSG_RESETALL: TWCP_NONE

Allowed Values: TWCP_NONE TWCP_PACKBITS TWCP_GROUP D TWCP_GROUP DEOL TWCP_GROUP D TWCP_GROUP TWCP_JPEG TWCP_LZW TWCP_JBIG TWCP_PNG TWCP_RLE TWCP_RLE TWCP_BITFIELDS TWCP_ZIP TWCP_JPEG

Containers

MSG_GET TW_ONEVALUE TW_ENUMERATION

MSG_GETCURRENT TW_ONEVALUE

MSG_GETDEFAULT TW_ONEVALUE

MSG_SET TW_ONEVALUE

MSG_SETCONSTRAINT TW_ONEVALUE

TW_ENUMERATION

MSG_RESET TW_ONEVALUE

MSG_QUERYSUPPORT TW_ONEVALUE

Required By

All Image Sources

TWAIN Version Introduced

Version 1.0

Related

CAP_XFERCOUNT ICAP_IMAGEFILEFORMAT ICAP_JPEGQUALITY ICAP_JPEGSUBSAMPLING