BLOB Filters
Go Up to Defining BLOB Data Types
BLOB
subtypes are used in conjunction with BLOB
filters. A BLOB
filter is a routine that translates BLOB
data from one subtype to another. InterBase includes a set of special internal BLOB
filters that convert from subtype 0 to subtype 1 (TEXT
), and from InterBase system subtypes to subtype 1 (TEXT
). In addition to using the internal text filters, programmers can write their own external filters to provide special data translation. For example, an external filter might automatically translate from one bit-mapped image format to another.
Associated with every filter is an integer pair that specifies the input subtype and the output subtype. When declaring a cursor to read or write BLOB
data, specify FROM
and TO
subtypes that correspond to a particular BLOB
filter. InterBase invokes the filter based on the FROM
and TO
subtype specified by the read or write cursor declaration.
The display of BLOB
subtypes in isql
can be specified with SET BLOBDISPLAY
in command-line isql
or with the Session | Advanced Settings
command in Windows ISQL.
For more information about Windows ISQL and command-line
isql
, see the Operations Guide. For more information about creating external BLOB
filters, see the Embedded SQL Guide.