12bitsThis filter is unlikely to be widely useful; it was developed due to a specific request on comp.graphics.apps.photoshop. It's probably most useful as a template/example/demo of a simple cross-platform filter.
It merely quantises each channel of an image into 16 values, essentially taking the most significant four bits of each pixel value and multiplying by 17 to keep the range from 0-255: output values are therefore 0*17,1*17...15*17 (255). A full colour RGB image will be reduced to a maximum of 4096 colours.
Source code is provided for building with