Filtering Blob Data
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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 (unstructured data) to subtype 1 (
TEXT), and from subtype 1 to subtype 0.
In addition to using these standard filters, you can write your own external filters to provide special data translation. For example, you might develop a filter to convert one image format to another, for instance to display the same image on monitors with different resolutions. Or you might convert a binary Blob to plain text and back again to be able to move the file more easily from one system to another.
If you define filters, you can assign them subtype identifiers from –32,768 to –1.
The following sections provide an overview of how to write Blob filters, followed by details of how to write an application that requires filtering. For more information about writing Blob filters, see the Embedded SQL Guide.
- Using Your Own Filters
- Declaring an External Blob Filter to the Database
- Writing an External Blob Filter
- Writing an Application that Requests Filtering