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Executable and Nonexecutable Filters

You can categorize custom Core Image filters on the basis of whether or not they require an auxiliary binary executable to be loaded into the address space of the client application. As you use the Core Image API, you’ll notice that these are simply referred to as executable and nonexecutable. Filter creators can choose to write either kind of filter. Filter clients can choose to use only nonexecutable or to use both kinds of filters.

Security is the primary motivation for distinguishing CPU executable and CPU nonexecutable filters. Nonexecutable filters consist only of a Core Image kernel program to describe the filter operation. In contrast, an executable filter also contains machine code that runs on the CPU. Core Image kernel programs run within a restricted environment and cannot pose as a virus, Trojan horse, or other security threat, whereas arbitrary code that runs on the CPU can.

Nonexecutable filters have special requirements, one of which is that nonexecutable filters must be packaged as part of an image unit. Filter creators can read “Writing Nonexecutable Filters” for more information. Filter clients can find information on loading each kind of filter in “Loading Image Units.”

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